The Most Complete Guide To Mammals Ever Made!

Well, hi there. The documentary that you are about to see is the most complete video guide to mammals ever created. This massive undertaking has been more than 3 and 1/2 years in the making. As such, you will observe many changes to our studio and my appearance as we take you through every family of mammals alive today. We're glad you're here.

This is a mammal. And so is this. And so is this. And so is this. And so is this. And so is this. And so is this.

Mammals are synapsids. As are animals like the Dimetrodons that came in many packs of plastic dinosaurs when at least I was growing up. They aren't dinosaurs. However, they are synapsids. Synapsids referring both to the clade to which they belong as well as the fact that they only have the lower of the two openings in the skull behind the eye, the temporal fenestrae that you find in diapsids like modern reptiles, the closest living relatives of mammals. So they only have one temporal fenestra on each side of the skull. Knowing that it is the lower of the two fenestrae will help you differentiate them from the now extinct eureptiles, which only had the top hole. However, this alone is not enough to help you identify a mammal. Dwarf caimans, for example, have only the bottom fenestra like mammals. The other has been secondarily lost. And the fossil record is full of non-mammalian synapsids, with Dimetrodon only being the most well-known.

Other features include the presence of fur or hair, a broad neocortex region in the brain, endothermia, a single bone lower jaw with three middle ear bones like this one from a whale, which is derived from some of the other lower jaw bones that are found in other amniotes. And most importantly, milk-producing mammary glands. Mammary glands are truly the feature that sets mammals apart from any other group, modern or ancient, and have probably been hugely important in their success as a group. Though there are fewer than 7,000 described mammal species alive today, meaning that there are literally more species of extant dinosaurs than mammals, but they are the largest animals on the planet today, with some being the largest animals ever known to have existed. They are intelligent, resourceful, and capable of colonizing parts of the globe that are inaccessible to the vast majority of other animals alive today.

Now, I want to point out two features of mammals that I didn't mention, largely because they aren't features found in all mammals, namely live birth and nipples. Many people are surprised when they find out that many lepidosaurian reptiles like snakes and other lizards give live birth. They often ask me, "So, is it a mammal then?" And the answer is, of course, no. Mammals are not the only animals to give live birth. And not all mammals do, because not only is egg-laying likely the ancestral condition of mammals, but there is a clade of mammals alive today that still do it: the outgroup to all other extant mammals, the monotremes of Australia and its nearby islands.

Monotremes have all of the features of mammals generally, but they lay shelled eggs and have no nipples, which are both pretty good things for them to mention when they play two truths and a lie. And for a lie, they could say that they have a connection between their brain hemispheres, a corpus callosum. Most mammals do, but it does not seem to be the ancestral condition, as it is lacking in both monotremes and marsupials, two of the three major lineages of mammals. Monotremes also have a sprawling gait with their limbs out to the side, as we tend to see in reptiles, as well as a single urogenital opening, a cloaca, something that we also tend to see in reptiles. They all have electroceptive capabilities and bioluminescence. So they're pretty weird for mammals, but they're weird pretty much all in ways that make them more similar to the ancestors of all mammals and even to modern reptiles.

Today, there are five species of extant monotremes in two families, and both are toothless as adults. And weird. The only one is venomous, and neither of them have nipples. So, I'd probably better talk about that before I dig into the two families. Mammary glands are such amazingly wonderful things that we named the whole group after them. They deliver the nutrients that a developing baby mammal needs in just the right ratios. But the method of delivery can apparently differ. And the reason for that is that mammary glands are terrific no matter how the milk gets to the baby. Mammary glands are exocrine glands, very similar to other exocrine glands like sweat glands. And in monotremes, milk is basically just sweated out through pores in the skin and then lapped up by the little puddles, which is legitimately what hatchling monotremes are called. So rad. Maybe not as targeted of a delivery as nipples, but it works. And evolution doesn't work with what would be best, but what exists. And in the lineage of monotremes, mammary glands exist, but nipples do not. Nipples might be better, but mammary glands with no nipples are a lot better than no mammary glands at all.

The two families are the family Ornithorhynchidae, the platypus, and Tachyglossidae, the four species of echidnas, one of which is named after David Attenborough. I normally don't approve of scientific names that don't simply describe something distinctive about the species in Greek or Latin, but if you're totally going to mess up naming conventions, naming it after David Attenborough gets my seal of approval. Especially if they say things like, "This delightful creature is an echidna." But I'll start with the platypus because it is a creature so weird that when the first specimens were examined outside of Australia, the scientists examining them had trouble determining if they were even a real animal. And it turns out that they are real, just extraordinarily unusual. So odd that it is very unlikely that you would confuse them with any other single animal, though perhaps a chimerical animal assembled by a wizard or rogue taxidermist.

They are found in and near freshwater habitats along the east coast of Australia and on the island of Tasmania, as well as an introduced population on Kangaroo Island. So there are such things as invasive platypuses, which probably makes them my favorite invasive species anywhere. Platypuses are fairly small and probably smaller than most people would guess, with males coming in at about half a meter long, about 20 inches, and weighing about 1.7 kg, which is well under 4 pounds. Females are even smaller than that, averaging just 43 cm, about 17 inches, and weighing less than a kilo, about 900 grams or 2 pounds. But they pack a lot of weird into that little package. I mean, they have all of the weird monotreme stuff, but so much more. Like the fact that they swim mostly using their pectoral fins. I mean, I mean, webbed forelegs for propulsion, like a pufferfish. They have hyperdense, waterproof fur, like an otter. Uh, in fact, otters are the only animals with denser fur, but this, of course, fluoresces cyan and green under UV light. They have a long bill that looks at a glance like that of a duck, but it has nostrils near the end, more like a kiwi, and is covered in skin, guess like an alligator. In fact, the nostrils are in the right place for an alligator, too. But the lack of teeth probably put an end to most alligator comparisons. It is covered in electrosensitive receptors like the rostrum of a shark. It has cheek pouches for storing food like a squirrel. They have no ear pinnae like a seal, and the ears close underwater a bit like an alligator, except the eyes are right next to the ears in the same groove, and that is what actually closes. So closing their ears actually also closes their eyes. I don't really have a comparison for that. They have a flat tail a bit like that of a beaver, but unlike a beaver, it is covered in fur and generally isn't used for propulsion, just steering, again like a pufferfish. Well, not the fur part, but the steering part. And it is a main fat reserve like a leopard gecko. They have a few teeth when they're young but lose them before reaching adulthood, as well as the electroreceptors, 40,000 of them. The bill is also covered with mechanoreceptors for touch. This is very important when they're underwater, as their eyes, ears, mouth, and nose are all generally closed when navigating underwater. Touch and electroreception are basically all they have to determine where they should put their head, shoulders, sprawled knees, and webbed toes, as well as locate prey. Sex determination is coded for by a host of chromosomes and probably needs its own video to explain. And while both males and females are born with a spike on the hind legs called an ankle spur, only the males retain it into adulthood. And it isn't just a spike. They have venom-producing glands in their thighs that are connected to the spur, allowing them to use it to inject venom into rival males and you if you cross one, leaving a wound that may be highly painful for months after envenomation.

We could probably talk a lot longer about them, but then when would we discuss their spiny, egg-laying land cousins, the four species of echidnas? You would never confuse an echidna for a platypus. Even if you had your nostrils, eyes, and ears all closed, one touch would tell you that you have an echidna, not a platypus. That said, they aren't as different from platypuses as you might think. Monotremes seem to have diverged from the other mammals at about the same time that dinosaurs diverged from the other archosaurs in the Triassic. So, not that recently. But the divergence between echidnas and platypuses was not that long ago at all, at least by comparison. And their shared ancestor seems to have been a semi-aquatic animal that looked and lived more like a platypus than an echidna. But modern echidnas live on land and feed primarily upon eusocial insects like ants and termites. They are sometimes called spiny anteaters. And all of that's true, but there are literally no mammals more distantly related to true anteaters than are echidnas. Whereas the range of platypuses is fairly small, echidnas are found all over Australia, its associated islands, and New Guinea. Not only is their range larger, but they are as well. Females can weigh about 10 pounds, 4.5 kilos, and males even more, about 6 kilos or 13 pounds. They are covered in thick, sharp keratinous quills on top with softer undersides. In addition to the quills, males also have a spur like that of male platypuses, but without the venom. They have a long, but this time skinny proboscis with a long tongue for catching prey and again no teeth as adults. Their proboscis has electroceptors on it, but not nearly as many as platypuses, and located near the tip for locating their prey. And they have short, powerful limbs with big claws for digging rapidly in search of that prey. And females have a pouch in which they incubate their eggs as well as house their little puggles. I really wouldn't mind making a whole video about the monotremes in the future where we dig, echidna-style, into all five species and how sex is determined in these egg-laying little oddballs. But right now, we have to talk about something else.

And that something else would be the placenta. Mammals, as we have discussed before, are the hagfish of reptiles. They are synapsids, more closely related to modern reptiles than they are to anything else alive today, but not as closely related to the reptiles as the reptiles, including birds, are to one another. Together with the reptiles, they comprise the living members of the Amniota. Amniotes are unified not only by shared ancestry but by the amniotic egg: shelled eggs with many membranes that allow amniotes to reproduce far away from water by effectively bringing the pond with them. When discussing the amniotic egg, I usually ask my class if they were to say, spend the next 6 weeks in a bathtub full of water, what they would need to bring with them to survive the experience. Generally on the list are food, clean water, a bag for um waste, and a dry suit or something to keep you somewhat isolated. Well, this is pretty much exactly what we find in an amniotic egg. The bathtub itself is made of a shell and a membrane just inside the shell called the chorion. If you've ever eaten a boiled egg, you are probably familiar with the chorion. Remember the chorion? It will come up again here in just a minute. But the shell and chorion are somewhat permeable to air but do not allow much water exchange. Food and water are provided by the yolk, also called the vitelline. Remember that one, too. The poop sack is called the allantois. It's French, but I always remember its name because I remember how much I hate that sack of poop. Allantois, stupid allantois. And just for the record, I I don't actually know anyone named Alan Towis, but I did find several on Facebook, so I might have just made a few enemies. Who wants to be friends with a guy named after a sack of poop anyway? And that dry suit, that would be the amnion, for which the amniotic egg gets its name.

So, back to mammals. There are three large groups of mammals alive today: monotremes, marsupials, and placental mammals. Though I find these names to be a bit misleading because two of the three have placentas. But the monotremes, they they just lay perfectly normal amniotic eggs. The other two groups, the marsupials and the placental mammals, they don't. These two groups, as I just mentioned, have placentas. And you've probably heard of a placenta before. If you've ever attended a mammalian birth, there's a good chance that you've seen one before. You probably even made one once. But you probably don't really know what it is or what it does. Most people that I've met think that humans and other placental mammals are connected to their mother or their mother's blood supply during pregnancy. The problem is that this wouldn't work. Mom has an immune system that seeks out things inside of mom that aren't mom and kills them. So does baby. If mom's blood went into baby, mom's immune system would kill baby, and baby's immune system would kill mom's blood. This is why you can't get an organ or blood transplant or transfusion from just anyone. But baby does get nutrients and oxygen from mom's blood and disposes of waste in the same way. And baby does this by getting its blood close enough to mom's blood so that diffusion can occur between them. And the placenta is the embryonic and fetal structure that gets baby's blood so close to the blood in the wall of the uterus that this can occur.

Now, I mentioned that both marsupials and placental mammals have placentas. For this reason, I prefer to refer to the placental mammals as eutherians. I'm fine calling marsupials marsupials, but I also frequently refer to them as metatherians, though metatheria is actually a larger group than marsupialia. There are non-marsupial metatherians such as this guy, Thylacosmilus. However, today the only extant metatherians are marsupials. So the two terms metatherian and marsupial can be used somewhat interchangeably when discussing extant metatherians. The real takeaway is that the marsupials and the eutherians are two different groups of placental mammals. But it is important to note that there are also two different kinds of mammalian placentas: one formed from the chorion and the yolk or the vitelline, called the choriovitelline placenta, the other formed from the chorion and the allantois, called the chorioallantoic placenta. And I wish I could say that marsupials have one and eutherians the other. But that's only partly true. It is the case that marsupials, well, they always have a choriovitelline placenta. And eutherians, they've always got a chorioallantoic placenta. But bandicoots also have a chorioallantoic placenta in addition to their choriovitelline placenta, despite being marsupials, and many eutherians develop a choriovitelline placenta before the chorioallantoic placenta develops. So, well, it's just not that simple. But what you probably noticed is that the choriovitelline placenta in mammals with both develops first and only works during early development. And that is because the choriovitelline placenta is low in surface area and can only support a very small embryo. Which is why a newborn deer looks like this. And newborn kangaroos like this. Did you notice the difference? Marsupials, due to their general lack of a chorioallantoic placenta, must be born extremely premature, at least by eutherian standards. And that probably begins to explain the most famous feature of marsupials, the pouch, which is possessed by most, but surprisingly not all, marsupials. But a pouch makes sense in many cases because that baby isn't ready for the cold and dangerous world just yet. It crawls up into the pouch, finds a nipple, something that monotremes lack, though they do make milk, and stays there for a very, very long time. Lactation is by far the longest portion of the early development of marsupials, whereas gestation is the longest part for most eutherians.

So, now that you know why marsupials make their way into pouches, let's talk about how they made their way from Antarctica to Australia and how they got to Antarctica in the first place, and why there weren't any eutherians when they showed up. As we mentioned earlier, the eutherian and the metatherian lineages diverged somewhere between the middle of the Jurassic and the beginning of the Cretaceous, way before Tyrannosaurus Rex even existed. But the earliest fossils of metatherians come from Cretaceous deposits in Asia and North America, which is odd, given that, well, marsupials are generally associated with Australia and to a lesser degree South America. In fact, mainland Asia and North America combined only possess two species of a single group of marsupials, the order Didelphimorphia, opossums. And none of them are in Asia. Most are actually found in South America. And the two species in North America actually migrated here from South America, which is funny because South America got its metatherians from North America. And now North America only has metatherians because it got a few back from South America when South America and North America came back into contact just a few million years ago. Opossums are the most distantly related group of marsupials alive today, in that all of the other marsupials are more closely related to one another than they are to opossums. Opossums are not to be confused with possums, which are more closely related to all of the other marsupials than they are to opossums and live on, well, the other side of the planet. While we only have one species in the United States, opossums are the most speciose marsupial lineage in the Americas with around 93 described species. Though Virginia opossums are larger than most people would think, opossums generally are somewhat small, with the largest getting to be about the size of a house cat. Most of them spend some time on the ground and some time in trees, though there is a semi-aquatic water opossum, which is now one of my favorite creatures. Their feet are plantigrade, and many have prehensile tails, and both their feet and tails often have scales, and their hind feet have an opposable kind of a toe-thumb with no claw. They generally have long, skinny heads with large sagittal crests and buckets of teeth, 50 to be specific, with tricuspid molars, and they like to show them off when frightened, though they're very uninteresting. While most species have pouches, not all do, but they do have the bifurcated penises and vaginas possessed by, well, most marsupials, so that's a plus. These come in handy because most opossum babies never make it to a nipple to nurse. Opossums just have a ton of babies and hope that a few make it to nutrients. And while that may seem sad, when your babies are born less than two weeks after mating, well, those are just the breaks. But the reality is that despite originating in the northern hemisphere, for most of the existence of marsupials, all of the other marsupial lineages today are relegated to the southern hemisphere, with South America serving as the hub of all marsupial distribution.

This includes the next most distantly related clade of extant marsupials, the order Paucituberculata, seven species of shrew opossums, which, like the possums that we will discuss shortly, are more closely related to all of the other marsupials than they are to opossums. Meaning that shrew opossums are more closely related to possums than they are to opossums. So, shrew opossum is it's a terrible name for them, though they do look a lot like shrews. They have tiny eyes and skinny faces, and they fill the basic niche of shrews, as shrews were absent from South America until South America reconnected with North America about 3 million years ago, when the true opossums made their way up to North America, high-fiving shrews as they passed one another. But basically, if you're in the Andes Mountains and you find a creature that looks and acts like a shrew, but it's a marsupial, it's not an opossum, but it is a shrew opossum. And that brings us to the last order of South American marsupials alive today: an order represented by a single extant species, the order Microbiotheria. Despite the fact that the one species, the Monito del Monte, is found in Chile and Argentina, all of its closest living relatives are not found in South America at all. They left. They are more closely related to the Australian marsupials than they are to any of the other extant American marsupials. The Monito del Monte, meaning little monkey of the mountain, really does seem like a pygmy marmoset and an opossum had a baby. They are arboreal with grabby little hands and feet, prehensile tails that are furred on top and naked below, dense fur with large eyes surrounded by dark rings, and 50 teeth, just like an opossum. Like I said earlier, their closest living relatives are not found on this side of the planet. They are simply the last surviving species in South America of a lineage, well, that colonized Australia.

But you may have noticed that Australia is not very close to South America and hasn't been for a very long time. You can't just walk from South America to Australia. However, before about 50 million years ago, you could walk from South America to another continent that we often forget about, Antarctica. Not only was it close, but it was a tropical paradise of sorts. And marsupials from South America were doing great down there. And Antarctica, which was previously connected to Australia as well as South America, was still very close to the land down under. It was actually just down under the land down under, to be more specific. Not close enough to just walk over, but close enough that colonization from Antarctica was not completely impossible. And it may have only happened one time, which explains why all of the marsupials in Australia and its neighboring islands all form a single clade found there and nowhere else. The biggest order within this single Australian clade called the Diprotodontia is also the largest of all extant metatherian orders with around 155 species, and that order would be the clade Diprotodontia. This clade includes many familiar marsupials such as kangaroos, wallabies, wombats, koalas, cuscuses, and other possums. Not to be confused with opossums or shrew opossums. I would actually really like to make a whole video just about this clade, especially considering that this group includes the now extinct marsupial lion, which is not a lion anymore than the shrew opossum is a shrew. It is now composed of herbivores, insectivores, and omnivores. There are two fairly conspicuous features that identify members of this group: first, their teeth, and second, their weird toes. This group is called the Diprotodontia, meaning two front teeth. They don't have to want them for Christmas because the members of the Diprotodontia, well, they have them. They have diprotodont teeth, specifically their lower incisors, they have two, only two, and then a big diastema before the molars, similar to what you see in rodents. Most diprotodonts have more than two upper incisors, but those two lower incisors are a strong indicator that what you have is a member of Diprotodontia. But if you're still not sure, take a look at their toes, not their front feet. Everything there looks pretty normal for a mammal. Take a look at their back feet. Now, the feet of a kangaroo are all kinds of weird looking. In some ways, they look like the feet of a paleognath bird, like say an emu or a cassowary, or other theropods like Tyrannosaurus Rex or Velociraptor. But if you take a long hard look at the innermost toe, the one that Dr. Grant would call the middle toe, you might notice something odd. It has two claws on it. And this isn't just the case for kangaroos either. It's all of the diprotodonts. They've all got it. Two toes fused together down to the last digit, resulting in what appears to be one toe with two claws, syndactyly. And this, combined with the diprotodont condition, will tell you that what you have is a true diprotodont. And this group comes the closest of any marsupial group to recolonizing the ancestral metatherian homeland of mainland Asia. They make their way all the way up to the Kei Archipelago, which is pretty much as far south as most Asian taxa go and as far north as most Australian taxa reach. And it is the only part of the world where marsupials are eaten by the best pet snakes in the world, reticulated pythons: the marsupial-eating super dwarf reticulated python of this archipelago.

But there are still three major clades of Australian marsupials yet to be explored. These final three are all more closely related to one another than they are to anything that we've discussed to this point. And the clade most distantly related to the other two is the clade Notoryctia. The marsupial moles that we discussed in our video on Afrotheria. These, like the golden moles in the Afrotheria, are not moles. These are actually even more distantly related from the true moles than are the golden moles, which are more closely related to elephants than they are to moles. But these are marsupials. More closely related to the last two groups we have to cover than they are to anything else. But the two species of marsupial moles are, well, they're more closely related to kangaroos and even opossums than they are to true moles or golden moles, which are both eutherians. That said, the level of convergence is astonishing. If you are in Australia and you find what appears to be a mole, well, it isn't one.

The two remaining clades are the two most closely related of any of the clades that we've discussed today. The smaller of these two groups will explain why we talked about both the teeth and the feet in Diprotodontia. And the larger of the two will allow us to talk about these, and when we might see them again. So, let's start small and work our way to cryptozoology and de-extinction. Peramelemorphia. These are your roughly 20 species of bilbies and bandicoots. You've probably heard of these before, but if you're not from Australia or New Guinea, you've probably never seen one outside of a video game. Well, this is a bilby, and this is a bandicoot. They look a lot like elephant shrews and rabbit-eared elephant shrews, respectively. But of course, they're not elephant shrews. Elephant shrews, like golden moles, are more closely related to elephants than they are to bilbies or bandicoots. Heck, they're even more closely related to actual shrews than they are to bilbies and bandicoots. And they're not very closely related to shrews at all, because bilbies and bandicoots are not eutherians. They're marsupials, but you probably know that by now. But like we mentioned earlier, the bandicoots have, in addition to the choriovitelline placenta found in all marsupials, a chorioallantoic placenta, but it is smaller than those found in most eutherians and it lacks the chorionic villi. Chorionic villi are small projections that finger out and greatly increase the contact area between the placenta and the uterine wall. What this means is that while bandicoots seem to be walking a similar evolutionary line to the uh, they are still born comparatively underdeveloped. So it's a good thing that they have a pouch like most other marsupials. Though the pouches of bandicoots and bilbies are backward-facing, similar to those of wombats or koalas, a convergence, as those are both diprotodonts.

And the closest relatives to the bandicoots and bilbies are, in my opinion, one of the coolest groups of marsupials on the planet: the Dasyuromorphia. This group includes the well-known Tasmanian devil, which I had the pleasure to meet in the Australian Reptile Park in 2019 on the one day that I have spent in Australia in my life. It was a fantastic day. Thank you, Patreon. If you'd like to see more content from Australia, please consider supporting us on Patreon. But this group includes more than just the Tasmanian devil. It also includes some of the Tasmanian devil's closest relatives that are, well, not so well-known, such as quolls, mulgaras, kowaris, and many others. Not to mention numbats, which have to be one of the cutest animals on the planet. And though it is currently extinct, well, at least we think, the Tasmanian tiger, also known as the thylacine, about 72 species total. Dasyuromorphs are carnivorous and subsequently have many morphological convergences with eutherians in the order Carnivora. I would honestly love to spend a whole video talking about just this group, also the Carnivora. So, let me know in the comments if you're into that kind of thing. But a lot of these look like smaller carnivorans like wolverines, weasels, and cats, as well as a large number that look basically like carnivorous mice or rats. And one group that is striped like a tiger but looks, or at least looked, like a dog, which interestingly may have been driven to extinction in Australia and New Guinea by the dingo itself, as well as the New Guinea counterpart to the dingo, the New Guinea singing dog, in addition to other factors. This would have happened just a little over 3,000 years ago, which is recently recently enough that we might be able to find enough DNA to bring them back, similar to what we discussed with the moas, elephant birds, and woolly mammoths. But there is a reason that we don't call these dog-like marsupials New Guinea or Australian tigers because there is a part of the range of the thylacine where dingoes and their canid cousins were not introduced: Tasmania, which is why it is often called the Tasmanian tiger or the Tasmanian wolf, despite being far more closely related to a koala than it is to tigers or wolves, which are both eutherians. Tragically, like wolves, throughout much of their range, they were viewed as a threat to livestock in Tasmania, and a bounty was placed on them. It is difficult to hunt species to extinction, but large carnivores are an exception because they can never exist in high densities like herbivores can. And being a low-density, easy-to-spot animal on an island means there cannot be too many of them. The last thylacine verified to be alive died in a zoo in Tasmania in 1936. We have videos of these alive. This is less than a hundred years ago. And a study of alleged sightings in Tasmania published this year by Brook and colleagues suggests that they may not have gone extinct in Tasmania until the 1980s or even into the early 2000s. And some people still claim to see them from time to time in Tasmania. But if they're alive today, and they genuinely may be, that probably isn't the most likely place where they may be found. Heck, Australia is so large and much of it so remote that they could still be alive in Australia somewhere. But honestly, the place that is most likely, in my estimation, for them to still be alive today is in New Guinea. New Guinea is the second largest island in the world, but it only has about 15 million people. For comparison, Japan is half the size of New Guinea and has 125 million people. It is heavily forested, and much of the island is completely inaccessible except on foot, and reports of sightings of thylacines by villagers in the remote parts of the island are not uncommon at all. If there was ever a place where a large nocturnal land predator could go undetected by the scientific community, the remote jungles of New Guinea, those seem like the place. But that isn't the only hope for the thylacine. Let's say that all of the thylacines are extinct. Well, we have specimens that we collected less than a hundred years ago. We've been able to successfully extract DNA from these specimens since 2002 and recently sequenced their entire genome. In other words, if we clone them, we wouldn't need to fill any sequence gaps with frog DNA or nothing. And just starting last year, a major effort is underway to clone the Tasmanian thylacine. So even if they're gone, and I have my doubts about that, they may be back very soon.

So those are the marsupials, which bring us to our final clade of mammals, the eutherian mammals, which today are represented exclusively by the clade Placentalia, those of the chorioallantoic placenta. Eutheria being all mammals alive or extinct, more closely related to placentalian mammals than they are to marsupials. And Metatheria being all mammals alive or extinct, more closely related to marsupials than they are to placentalian mammals. Due to the fact that the chorioallantoic placenta has considerably more surface area than does the choriovitelline placenta, babies can become, as we discussed earlier, much larger before being born. Meaning that there needs to be more space in the abdominal cavity of females and the birth canal needs to be much larger. As such, placentalians have lost the epipubic bones of marsupials and monotremes that extend into the abdominal cavity and have developed a much wider opening at the base of the pelvis. Unrelated, but also new, they no longer have a cloaca, but instead multiple openings, including separate openings for the urethra and anus, as well as, for the first time, a corpus callosum connecting the hemispheres of their brains, and a few other unique skeletal features, especially in the bones of the legs, if they have legs. Not all do, but they are a very unique and highly successful group containing over 80% of mammalian families. So I guess I'm saying that we're just getting started. And the Placentalia itself is made up of two major clades: one with you and whales, and the other with armadillos and manatees. Meaning, of course, that manatees and whales are as distantly related to one another as any two extant placentals. And I think I'll start with the whale clade because whales were the first mammalian clade that we ever discussed on this channel. Plus, it includes a lot of small groups that we've never discussed before, as well as the fact that it allows us to get to the pinnacle of creation a bit faster, and it will give us an extra strong appreciation for the ridiculous convergence that we will find in Afrotheria when we get to them.

So, this clade, Boreoeutheria, includes two clades: the Euarchontoglires, things like flying lemurs, tree shrews, and you, and the Laurasiatheria, things like bats, true shrews, and shamu. And since I'm trying to get to the pinnacle of creation as soon as possible, you know where we're going. Now, this clade also contains two clades. And again, you know where we're going. But before we get to the primates, we need to take a quick stop at their closest relatives: the two species of colugos of the family Cynocephalidae, the only family in the order Dermoptera, the skin-wings. Colugos are often called flying lemurs, though neither of those things are true about them. They neither fly nor are they lemurs. In fact, if they were lemurs, then you would be a lemur, too. But they are bodacious. Found in Southeast Asia and the Philippines, these guys are totally bizarre looking, looking like giant flying squirrels from Dark Crystal or something directed by Tim Burton. While they don't fly, they are quite capable gliders, capable of traveling as far as 70 meters between trees without touching the ground, which is good 'cause they're pretty terrible on the ground. And that is pretty far for an animal that is only 35 to 40 cm long, weighing just 1 to 2 kilos, under 4.5 pounds. This astounding gliding is possible because of a flap of skin called the patagium that connects their front legs and their back legs and from their hind legs to the tip of their tail. They even have webbed feet. Basically, if there is something that can be connected by skin to increase surface area, colugos have it. They even have a membrane that connects their thumbs, which are not opposable like they are in primates, to the sides of their heads. Their snout is really the only part of their body that isn't used to make a parachute. The snout that, along with their large forward-facing eyes, is probably what reminds some people of lemurs. But their non-opposable thumbs and claws instead of nails quickly give them away as not being lemurs. Unless not all lemurs are primates, in which case you'd be a lemur, too. Since you are more closely related to true lemurs than true lemurs are to colugos. Lemurs are among the closest relatives of colugos. But the opposite is not true because true lemurs are primates, and as such, all of their closest relatives are primates.

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Primates can be identified by their relatively large brains, large forward-facing eyes, opposable digits on their hands and or feet, and nails as opposed to claws. The primates form two clades: the Haplorhini and the Strepsirrhini. And right here, I want to address a major misconception that many people have: the Haplorhini and the Strepsirrhini are both equally evolved. Because evolution only has one goal: the survival of genes. And since all individuals die, this means that the goal of organisms is to pass their genes on to future generations. Many individuals may not know that this is the goal, and they may not succeed at doing so. And the result of this is that the genes of individuals that stink at achieving this goal are not well represented in future generations. The genes that make it to future generations are disproportionately and non-randomly the genes that assist with that one goal. Though random forces can have an impact too, especially in small populations or with respect to what mutations occur and when. But by and large, gene variants that increase the likelihood of an individual possessing them achieving the goal of passing on its genes become more prevalent over generations. Importantly, being a human is not the only way to achieve this goal. And the more similar you are to humans, the more directly you compete with them. What I'm saying is that other organisms are not failed attempts at becoming humans, nor is there a particular evolutionary pressure to become more like humans. If anything, the opposite is true. Humans [snorts] are great at being humans, but they make lousy strepsirrhines.

Strepsirrhines are identifiable by their wet noses, like those of a dog or a cat. Though Strepsirrhini means something like "turned around nose" or "turned around nostrils" in reference to their comma-shaped nostrils. They also make their own vitamin C. Remember that. It's important. And not just because you need vitamin C, though you do, you scurvy dog. Which is an odd thing to call somebody because dogs make their own vitamin C. In fact, almost all mammals make their own vitamin C. Very few do not, but we'll talk more about them in a moment. So, like dogs, strepsirrhines make their own vitamin C and have wet noses, which greatly increases olfactory ability. And the strepsirrhine clade itself is divided into two large groups: the Lemuroidea, lemurs endemic to Madagascar, and the Lorisoidea, the lorises and bush babies of Africa and Asia. Lemurs are such a rare group that they could definitely get their own video at some point. Now, lemur means ghost. There are around 100 species in Madagascar, eight distinct families, ranging in size from about 30 grams, about a 15th of a pound, to around 9 kilos, 20 pounds. That's now. When humans arrived on the island around 2,000 years ago, there were lemurs the size of gorillas. They are basically the monkeys of Madagascar, though they aren't monkeys, but they're rather convergently similar in many ways since there were no monkeys in Madagascar until we showed up. So all of the monkey niche space was wide open, and the lemurs filled it. Now, you're unlikely to confuse most lemurs with monkeys. And not just because of their location, wet comma noses, and vitamin C synthesis, but because their faces tend to look more like those of carnivorans than those of monkeys, with long, pointed snouts and ears that look more like a dog's than they do like, well, yours generally. Though that breaks down a bit with some groups like the sportive lemurs and my favorite lemur, the Aye-aye, which looks more like a gremlin, and not one of those happy gremlins. It's a monster. I love it. Now, most lemurs have front teeth called toothcombs. Not just them, but also the lorisoids that we will discuss soon, and the flying lemurs. So, it may be the ancestral condition of the Primatomorpha. Anyway, the Aye-aye, it doesn't have one. Instead, they have some crazy paired, continuously growing incisors. The skull looks like what you would get if you crossed a rodent with a parrot. Those incisors be crazy. But why be they crazy, Clint? Oh, I'm so [snorts] glad you asked. Because their eyes are woodpeckers. But instead of pecking holes in trees, they chew holes in trees. And why make holes in trees? Because there are tasty insect morsels in there. But how do they know where they are? You ask the best questions. They listen for them with their hideous, grumpy gremlin ears and their long, freaky knocking finger. Look at that finger. It isn't really so much long as it is skinny and terrifying. And it is terrifying. That knock is one of the scariest sounds a grub could ever hear. That and "Hakuna Matata." Once it has located a grub, it chews a small hole in the tree and then inserts the spider-like death finger into the hole, hooks the disappointed larvae within, and then hauls it out so that it can be masticated and ingested. What a wonderful beast. Now, I mentioned that the largest of all lemurs was about the size of a gorilla. And that's true. They were called sloth lemurs. But the largest extant lemur is the Indri, a close relative of the extinct giant sloth lemurs. And in addition to being large and colored like a panda, they also have a very short tail like a bear. But interestingly, not much like a panda. Pandas have huge tails for bears. But I want to ask you a question: If the descendants of Indris eventually lost all external vestiges of their tails, would they cease to be lemurs? No. An organism cannot evolve out of a clade. Oh yeah, thank you.

Okay, so we have a pretty good idea how to distinguish lemurs from monkeys. But what about from their closest relatives, the members of the clade Lorisoidea? Well, a good place to start is by asking yourself the age-old question: Am I in Madagascar? That should handle the question. But to be perfectly honest, unless you have the ability to examine its DNA or look at its internal anatomy, it's otherwise pretty difficult to answer this question. This is a bush baby, also called a galago. It's adorable. It obviously has big front-facing eyes, somewhat opposable thumbs, and fingernails. It's a primate. It has a pair of wet commas, so you can probably guess about whether or not it can synthesize vitamin C. It can. And you could double-check yourself by looking for a toothcomb. It has one. This is a slow loris. Same deal. But in addition to that, it also has a toxic bite, used primarily in slow-motion battles with other slow lorises. But you know what? It doesn't have a visible tail. And you know what that means? It's no longer a member of the Lorisoidea. It evolved right out of that clade. Right? Of course not. It just doesn't have a tail. They could evolve to not have a head. And that wouldn't change the fact that the descendants of the first lorisoids will always be lorisoids. If you're in Asia or Africa and you find a soggy commoner with or without a tail, you'll know that you have a member of the Lorisoidea.

But the Strepsirrhini is really not the primate lineage that we're most interested in exploring because the monkeys are part of the other big primate lineage: the Haplorhini, the simple-nosed primates with dry, non-commal noses and no ability to synthesize vitamin C. These are the scurvy primates. And scurvy probably doesn't increase your likelihood of passing on your genes. So why hasn't this been a problem? Well, largely because most primates have diets rich in vitamin C. Haplorhines might not make it, but that wasn't really an issue. They didn't need to make their own. Not an issue, at least until primates started to live in places where foods rich in vitamin C were uncommon, especially say, at sea for months at a time. But there is a reason that I bring it up. What is the simplest explanation for why this entire clade would lack the ability to synthesize vitamin C? All of them. Now, it could have happened multiple times and been successful, or at least not devastating, repeatedly. But the simplest explanation is that the mutation occurred in the haplorhine lineage somewhere after the split from the strepsirrhine and reached fixation in the population before the first split within that lineage. Of course, just because it's the simplest, that doesn't make it true. So, how would you know? Well, the enzyme needed to synthesize vitamin C is coded for by a gene called GULO. And the GULO gene is roughly 22,000 base pairs long. If it is broken, it won't make vitamin C. And the

The likelihood of the same exact break happening independently in two different lineages is astronomically small. Guinea pigs are one of a small number of other mammals that have a mutation to their GLO gene, resulting in a lack of vitamin C production. Unsurprisingly, it is a different break from that found in haplorines, which makes sense. Same thing goes for the bats that don't produce vitamin C. It's a different break from the one that you find in guinea pigs or in haplorines.

But what about among the haplarines? Well, it's the exact same break straight across the board. And again, it happened before the first haplerine lineage diversified from the rest. That first lineage to diversify away after this break would be the tarscopiformies. Today represented exclusively by the family tarscied of maritime Southeast Asia. The tarsciers.

Now the first thing that you might notice about tarsciers is that their rostrm is much more flat than that of the streperini [snorts] reflecting the fact that these are less reliant on olfaction. But that's not the first thing that you noticed, was it? It was those colossal freaking eyeballs that they've got. If not, you're probably just listening to this video because how [laughter] could you miss them? They are enormous. In fact, in many cases, each individual eye is larger than their entire brain. And these guys are hapllar. They aren't smallrained. They're just giant eyed. I mean, look at the skull of this thing. Where would you even put a brain?

But somehow that wasn't the feature that caught the proportionally tiny eyes of the researchers who named them. Tarscier is due to their long footbones called tarscels, which give them very long legs, or more accurately, very long feet. But I'm not done with those eyes yet. Because if you look at them, they are always looking directly forward with the most intense stare you have ever seen in your entire life. Though owls may give them a run for their money because owls like tarscers are always looking straight ahead. You have never seen such determination in the eyes of anything else. And there is a good reason that they never side eye anything. They can't. Their eyes are too big. The muscles required to move those eyes would be huge and heavy. Not good for a bird or a primate. So they can't. They can see really well, but only what is straight in front of their faces. Which means that if they're going to see, say, uh, behind them, well, they will need to turn their whole head backwards like some sort of possessed wideeyed cowboy doll. >> We toys can see everything.

Now, they can't do the full cowboy, but they can spin it all the way to the rear, 180°, giving them the ability to see in any direction without moving their bodies. And somehow, vision might not be their primary tool when hunting. Like owls, tarscers are nocturnal and rely heavily on their hearing. They have big, thin ears like a bat, and their brains are particularly adept at processing auditory information. It really is like a wizard tried to make an insect eating owl out of a leaping monkey. Mission accomplished, but it isn't a monkey.

And that gets us to our mission, monkeys. And uh are you a monkeykey's uncle? Everything we have discussed so far can easily be excluded from the smallest cate that includes all of the monkeys. But now we are moving into the clay seam formies. And the group of seamies least related to all of the others is a caid of monkeys. And I think it is fair to say that a cate of monkeys cannot be removed from the smallest caid that includes all of the monkeys. Do we need to verify that with AI or are we all on the same page? So monkeys are monkeys. Okay. Okay, I'm going to work under the assumption that we can agree that monkeys are monkeys.

And this cate the platterini, the flat or broad-nosed monkeys are monkeys. Because flat-nosed monkeys live exclusively in the Americas. And because they are the only Simeians native to the Americas, they are often referred to as new world monkeys. The other clay in the semimeformis, the katarini being entirely from the old world are often called the katarine monkeys or the oldworld monkeys. Though the latter is often applied exclusively to one single cate of katarine monkeys and uh we'll get to them soon enough. But what we can see is that the two remaining clades in this lineage, they're both monkeys. New world and old world monkeys.

For the moment, let's talk about new world monkeys. the Platterini. Today, there are five living families of New World monkeys. Like all Simeians, New World monkeys have large, but not insanely large and therefore movable eyes with great daytime color vision, accompanied by large brains that specialize in visual perception more than a faction. Interestingly, while both the new world and old world monkeys have large brains, even for primates, they seem to have evolved those larger brains independently from one another, which isn't the case for their lack of ability to synthesize vitamin C. They both seem to have inherited that from the same haplorine ancestor. And I know that because once again, all of the Haplarines look to have inherited it from the same common ancestor. And the last common ancestor of all Haplerines as well as all of their descendants. So everything from that point until now have all been Haplerines. And I know this because that's how monopilletic groups work. You probably get this, but I have encountered evolutionary biologists that seem to still struggle with this concept. So I'm just being really explicit.

So what makes new world monkeys unique from old world monkeys other than geography? Well, let's start with their noses. Their names both refer to their noses. New world monkeys are the platarini, the flat-nosed monkeys, and the old world monkeys are the katarini, the downnosed monkeys. It really just has to do with the position of the nostrils. New world monkeys have side pipes, like a Dodge Viper, a Shelby Cobra, or a 427 Corvette. American cars, American monkeys. Not every American car has side pipes, but face it, you'd be shocked to see side pipes on a Ferrari, a BMW, or a Toyota. Now, why? Because the old world doesn't do side pipes. Oldw world monkeys point down. Well, unless they're snub-nosed monkeys that have the same plastic surgeon as Michael Jackson and Skeletor and He who shall not be named and Red Skull. Those last two are from the old world. Really not sure if the first two are even from this world. Great dancing though. >> [music] >> But the point is that new world monkey nostrils point out the side, not down. And so there is a much greater space between the nostrils. They are also the only monkeys that have prehensile tails. Not all of them have prehensile tails, but you'll never see a prehensile tail with downpipes. Prehensile tails have actually evolved two different times in New World monkeys, but never in the old world. They also have 12 preolars instead of eight, but that can be difficult to count at the zoo. It would be fun to do a whole video just about this group, but right now we're on a mission.

And that mission will require us to dig into the down-nosed oldworld monkeys of the Katarini. Now, you probably already know how to distinguish these guys. They have all of the attributes of other Simeians and can be distinguished from the New World monkeys by their nostrils that don't point out the sides, as well as the fact that they have eight preolars. And they never have prehensile tails. Some don't have tails at all, which as you know means that they've evolved right out of a clay. No, an organism cannot evolve out of a clay. Oh yeah, silly me. Anyway, they also tend to have flatter finger and toenails and much more opposable thumbs unless they've lost their thumbs, which means that they have lost their thumbs. That's it. Colibus monkeys are still monkeys because you can't evolve out of a clay no matter what you lose. Unless it's all of your ancestors. It's a heck of a thing to lose. So, you can identify a Katarine monkey with or without a tail or thumbs. Thumbs up if you got them.

So, what's in this group? Well, these and these monkeys. See the narrow septum between the nostrils? Now, did you notice that one of them didn't have a tail? And remember what that means? Yeah, it means that it doesn't have a tail. Now, there are two different lineages of catarene monkeys. The copathia and the homoidia. This guy is a copiiththeid and this guy is a homoid. The easiest way to distinguish between the two is to look for the tail. Homoids don't have them. Copycooids do. There are other differences if you get a good look at the cusps of their mers, but the presence or absence of a tail is the best giveaway, though it's not exactly foolproof. Barbar Macaks and crested black macaks, for example, are circids and their tails are tiny to non-existent, which means that they they have no tails. Anyway, the circopyids are often referred to as the oldworld monkeys. But as you may recall, that name was already taken by the Katarini. And given that circopycooids are part of this group and that all of the katarini is an entirely oldworld group, the question as to which group most deserves the title is simply whether or not all members of the katarini are monkeys or if only the copithoids are monkeys. And so we're going to need to back up and take a look at the phloyny for just a second.

What is a monkey? I think before we agreed that monkeys are monkeys and therefore new world monkeys, the platarini are monkeys and I've never seen anybody contend that the circids are not monkeys. Can we agree that both of these groups are monkeys? Now, we could very easily say that all primates are monkeys or all mammals, but that seems a bit overroad. Let's instead make the smallest possible monopilletic group that we can for monkeys. the smallest group that can be created that includes all of the animals that we all agree are monkeys, their most recent common ancestors and everything that came from those ancestors and absolutely nothing else. We will exclude every animal that we possibly can without creating a paraphilletic or polyphilytic group. The smallest monkey clay possible.

So what's the last common ancestor shared by both the platarini and the sarcopathicia? Well, that would be uh these guys right here, the first true monkeys. I'm sure that whatever came before them was very monkeyike, but I can exclude everything before this point from the monkey group, at least if I want to. But not these. These are monkeys and so is everything that came from them because that's the way that monopily works. And if we look at who came from them, you will notice that the platarini came from them. The circopyidia, they came from them and so did the homoidia. I can't exclude the homoidia from the monkey caid because they share ancestors more recently with the circopyidia than the ccopathicia do with the platarini. This means that while I could potentially justify excluding the platarini from the monkey caid I cannot exclude the homoidia from any caid that includes both platarini and circopyidia. It isn't possible. In a nutshell, the circoids are not the only oldworld monkeys. They are just the only old world monkeys with tails, even though not all of them have one.

So, that brings us to the tailless oldworld monkeys, the homoidia, the manlike oldworld monkeys. And what is so manlike about them? Well, like men, they have all of the basic attributes of primates, not to mention the attributes of utherans, mammals, synapses, vertebrates, cordates, duterosomes, biotitarians, etc. So, they have relatively large brains, large forward- facing eyes, opposable digits on their hands and or feet, and nails as opposed to claws like men and every other primate that we've discussed so far. But that is not where their similarities to men end. They also have all of the attributes of haplorine primates. So, they have dry noses and can't make vitamin C. And they can't make vitamin C due to the same change in the GO gene as the one that we see in uh men and women, just in case you were wondering. But that isn't where the similarities end either. Like men, they also have all of the attributes of Simeians, which is the smallest cate that can be created that includes all of the monkeys. attributes such as even larger brains that prioritize vision over all faction and movable eyes with great color vision. And that's not where it ends. The homoids also share all of the attributes of catering monkeys with men. So their nostrils point down and have a small septum between them. They also don't have prehensile tails and their thumbs are fully opposable uh and eight preolars. But that's not where the similarities end either because they also share all of the attributes of homoids. For example, they don't have a tail. But more than that, they don't have a tail for the exact same reason. They all share the same insertion mutation to the TBXT gene that plays a big role in tail vertebrae formation. Do you think that's the same mutation that you see in tailless macaks? I don't think that analysis has been done just yet, but I'd be very surprised if it is. And that's not the full extent of the similarities between homoids and men, just some of the most conspicuous ones, but plenty enough to help you identify a homoid when you see one, and plenty enough to justify calling them manlike.

So, let's dig into these man-like monkeys. And let's start with the least manlike of the man-like monkeys, the Hyo badday, the forest walkers, as opposed to the forest runners. >> Run forest, run, run, forest. Hyobataday is composed of the roughly 20 species of gibbons. And just at a glance, you can probably distinguish a hyobatid from the other homoids in the family hamminad. Hyobatids look much more like the monkeys that we've discussed so far. Just typical tailless catarene monkeys that aren't macaks. Macaks have a very distinctive face in case you're struggling. They're smaller than the other homoids and they tend to be built more for swinging around in the trees than are the homminids. Their long arms and ball and socket wrists make them the fastest of all brachiators, tree swingers, and one of the silliest of forest walkers. They also have some key behavioral differences compared to homminids. They tend to pair bond more than homminids, probably leading to reduced levels of sexual difference, sexual dimmorphism compared to homminids. They also do not tend to build nests like the homminids do.

And on that note, let's talk about the nest building tailless oldworld monkeys in the family homminid. The manlike man-like monkeys. Manlike monkeys are often referred to as apes. And the manlike man-like monkeys are often referred to as great apes. Possibly because they are bigger. Possibly because they're a little more hanky panky. And possibly because the more manlike a man-like monkey becomes, the greater we think it is. Though, I think it has more to do with the size. Because in my opinion, gorillas are greater than bonobos. Even though they're not quite as manlike. And nothing is more hanky panky than a bonobo. Except for ducks. They're screwed up. Anyway, today there are only eight or nine species of man-like man-like monkeys. Those are in order of relatedness to the pinnacle of creation, orangutans, three species, homminins, three species, and the pinnacle of creation, gorillas, two or three species. We should do a whole video just diving into these nine species. But right now, we need to dig a bit deeper into the closest relative to the pinnacle of creation, the homminini. The manlike manlike man-like monkeys. Not the greatest of the apes, but the most manlike. There are three extent species of man-like man-like man-like monkeys in two lineages. Pan, the chimpanzees and bonobos, and Homo, the well, us. While chimpanzees and bonobos are more closely related to one another than they are to us, and they aren't the closest relatives to us known to have ever existed, they are our closest living relatives and are more closely related to us than they are to gorillas, orangutans, gibbons, any other monkeys, any other primates, or anything else alive today. Other than the women, they are the most manlike of all primates that aren't men. And the men while tailless are nonetheless still great apes which are still apes which are still catarene monkeys which are still monkeys which are still primates because that's the way that monopily works.

The other cate in the urontoliers is a bit larger still. In fact it is one of the largest of all mamalian cles probably the largest catees that included though most of its members are relatively small. Not all though. But this creature is fairly small. It's a tree shrew, though not an actual shrew. We'll get to them soon enough. There are actually 20 species of them in two families. 19 of those species in the family tupied and the remaining species, the pentailed tree shrew in the family tilosid, which has a crazy cool tail that looks a bit like a big feather. More like if you tried to breed a rat tail with a feather pen. Tree shrews in general are kind of squirrel-like animals, only distantly related to shrews, but more closely related to squirrels, with a head that looks a bit like a kugos, to which they are also related, though not as closely. And interestingly, they have the highest brain to body mass ratio of any mammal, which doesn't mean that they're smarter than us, but it demonstrates that brainto body size ratio isn't everything. And pretty soon we'll talk about some animals with brains that are both larger and more complex than ours, which is interesting indeed. High brain to body mass ratios are fairly common in smaller animals. And these are fairly small, especially the ones that actually live in trees. Not all do. So none of them are shrews and only some of them live in trees. But they all have big brains and are found in South and Southeast Asia and the surrounding islands. So around the same places where you find kugos. But you won't mix them up because these guys aren't all webbed up in skin from head to toes and tail.

Their closest relatives include squirrels, but not just the squirrels. These guys aren't rodents, but rodents and the closest relatives of rodents, the lagamorphs, are their closest relatives, which together form the clay glars. And I'll confess, I was fairly deep into my degree in zoolology before I discovered that lagamorphs are not rodents. This is the skull of a lagamorph. And at a glance, it looks very much like the skull of a rodent. It has a conspicuous pair of everrowing incizers, though without the orange coloration that is fairly common in most rodents. A gap called a diasta, and then some mers. A very familiar formula if you're familiar with rodent skulls like this one. But if you look behind, and I mean uh directly behind those ever growing insizers, you will notice something that you won't see on a rodent. A second pair of tiny teeth called peg teeth. Those are unique to the closest relatives of the rodents, the lagamorphs. The other things that set them apart are that their teeth grow continuously, not just the incizers, and they have fur on the bottom of their feet. Females are often larger than males. Oh, and uh males have their testes in front of their penises, which also generally lack a vacculum. That's a fun little tidbit to use as an icebreaker at fancy parties, right before you talk about the pseudo penis of hyenas, which aren't canids, but we'll get to them soon enough. There are today two families of extent lagamorphs. the 70 or more species of rabbits of the family leapor including the 30 species of hairs which are nested right in with the other rabbits just like tortoises with turtles or birds with the reptiles not like mammals with reptiles more like snakes with reptiles. The other family being the more than 30 species of pikas in the family ootiday. Rabbits are probably a pretty familiar group to most of us thanks in some cases to the help of humans. They're found pretty much everywhere that we are. They have big hopping legs, short tails, long ears, and the general attributes of lagamorphs. Pikas, on the other hand, are more limited to cold climates, often higher altitude climates in North America and Eurasia. Their back legs aren't as long as those of rabbits, though their tails are still small, and their ears are more rounded, again, with the host of typical lagamore features like furry foot bottoms and penises thoughtfully tucked behind their testicles. though some do have a small bulum.

Their closest relatives to all of the lyamorphs comprise the largest single cate of mammals on the planet, the rodents. This is a rat. And this is a rat. Of course, if both of those are actually rats, then so is this. And so are all of these. So, it's probably just the case that kangaroo rats are not true rats. But if all of these are mice, then so are these. So let's start with things that are definitely mice. I mean mice of the family mirday, the true mice. The name mirday comes from the Latin moose, meaning mouse. So if there is one family of mice on this planet, it's this one. Obviously, it contains the genus moose, the truest of the true mice. Of course, even the subf family of the true mice that contains the truest of the true mice, Mirin, also contains well gerbles and a whole bunch of things called rats, including the truest of the true rats, the genus ratus. So rats, at least true rats, are mice. True mice, though not the truest of the true mice. And rats, as we will discover, are pretty much any rodent that you feel like calling a rat. But even true rats are mice, as are gerbles. And this is one of, if not the largest of all rodent families with nearly 900 described species. And somewhat surprisingly, with those 900 species, there are no murids, no true mice native to the Americas. They're native to Africa, Asia, Europe, and Australia, but are only introduced to the Americas. They're generally rather small with the smallest the African pygmy mouse only reaching about 8 cm, with half of that just being tail. Though, the northern Luzon giant cloud rat gets over 3/4 of a meter long and weighs over 2 1/2 kilos. That's considerably larger than a ferret or even some dogs. They're more than 200 times the size of a pygmy mouse. But let's be honest, they're still pretty small. Just enormous for a mouse. But if you had to fight the largest member of some mamalian cate in the coliseum and they wheeled in a giant cloud rat, you'd breathe out a pretty big sigh of relief. Just be thankful it wasn't a lagamorph. >> THERE'S NO ORDINARY RABBIT. THAT'S THE MOST FOUL, CRUEL, AND BAD TEMPERED RODENT YOU EVER SET EYES ON. >> Though rabbits, well, they're not rodents. >> HE'S GOT HUGE SHAP ABOUT. LOOK AT THE BONES. >> OKAY, let's

This is the skull of a rodent. And this is a jack rabbit. It's not a rodent. Now, the most conspicuous similarity about both of these skulls is that they have a pair of huge continuously growing sharp incizers. In the case of the rodent, they have an orange covering on the outer edge that the jack rabbit lacks. But this covering is also absent in guinea pigs, and they are rodents. So, that isn't what distinguishes rodents from their closest relatives, the lagamorphs. It's actually what's behind them. Not the diasta. They both have a large space between the insizers and the molers. But if you look behind the insizers of the jack rabbit or any other lagamorph for that matter, you will notice that there's an extra pair of mini insizers hiding back there. These are called peg teeth or pivot teeth. >> Pivots. Pivot. >> Also in lagamorphs, all of the other teeth grow continuously, not just the insizers like in rodents. And they have more cheek teeth than do rodents. These teeth over here. You can see that this rodent has only four cheek teeth on each side of the skull, top and bottom. And you can't see this from the skulls, but lagamorphs have fuzzy foot bottoms without pads, which is very different from what you see on a rodent.

But I want to get back to murids. You know, mice like true rats and gerbles. mice. In general, they have long, relatively thin bodies with long scaled, not furred, tails, and pointed snouts. >> The pointy kitty took it >> and long whiskers. Though there are exceptions to basically all of those rules. They have typical rodent dentition. On each side of the skull, they have one insizer, no canines or preolars, just a big diasta, and then one to three molers. So, even fewer mullers than this rodent and way fewer than the lagamorph. But a while back, I saw a video about a rat that people train to find landmines, the African giant pouched rat. As someone who loves rats, and I do love rats, this was pretty much the greatest thing I had ever seen. I really want to spend some time with these amazing rats. Even though, as it turns out, [clears throat] they aren't rats at all. At least they aren't true rats or even close relatives of true rats. They aren't even true mice. They're a whole different family, the African family, nisomiaday. In our video about the afrotheria, as well as many other videos, we've discussed the unique biology of the animals on the former island continent of Africa and its island neighbor, Madagascar. Well, it turns out that mice have a similar story to tell because while the Murids were diversifying in Eurasia, the Nisomiads were following a similar path in Africa. And it makes some sense that they evolved so similarly, they are one another's closest relatives. So, while they aren't true mice or true rats, they are isolated Africa's equivalent. the climbing mice, African rock mice, swamp mice, pouched rats, hamster rats, pouched mice, fat mice, short-tailed rats, tufted tailed rats, big-footed mice, and white-tailed rats, among others. 68 total species. They fill the basic ecological niches of mice, rats, vos, and hamsters. And though they aren't really any of those things, uh, we only know that because of genetic sequencing and a growing understanding of plate tectonics in history. The reality is fossils of tiny rodents are relatively uncommon. So these African and Malagasi rodents historically were just lumped in with whatever they most resembled. And they are the hagfish of true mice. So it would be possible to call them mice. But we would still need to understand that rat is just a word that means something like big mouse. It'd be fun to make a video about just this family in the future. And if anyone has a pouched rat, I need to make a video about those rats. True rats are our current mammal champions after all. And these seem at least at a glance like they might be even better.

So, the families Mirday and Nisomiaday could together be considered the mice. But what about this creature? It's a deer mouse, which ignoring the propensity to carry nasty diseases like haunt virus has got to be one of the cutest animals on the planet. And for the record, in general, you can contract more diseases from organisms that are closely related to you, largely because their physiology is very similar. And other than the animals discussed in this video, humans have no closer relatives than deer mice and the other glars, the rodents and lagamorphs. So, while you can't get much from a reptile, you can get a lot of diseases from a mouse as well as whatever this is. Because deer mice are not in the families Mirid or Nisomiaday. They aren't even from the right side of the planet to be from either of those families because they are from the Americas. And nothing else that we have discussed so far has been native to the Americas. And though this family, the family chet originated in Eurasia, it is the only group that we have discussed so far to have made its way to the Americas without human assistance. And with nearly 900 species, it is in contention with the mirday for being the largest family of rodents and indeed mammals in the world. Now, do you remember the African pygmy mouse that we mentioned a moment ago? Well, the Americas have their own pygmy mouse that is well, it's like the exact same size. And you know what? This new world pygmy mouse is not closely related to the African pygmy mouse. You know what? It is closely related to this. And do you know what? I always assumed that this creature was closely related to this. Yeah, those aren't the same thing. Deer mice, new world pygmy mice, and this thing are all chetids. This thing, by the way, is a muskrat. It's obviously not a true rat, but it is closer to being a true rat than it is to being a true beaver. Though, it is more closely related to beavers than are the mountain beavers. We'll get to beavers, but you have to admit muskrats look like slightly smaller roundtailed little beavers, but they're closer to being mice. In fact, if deer mice are mice, then they are mice. Big old water mice. And so are all of the other chettids and everything else we've discussed so far. The family cry today obviously includes deer mice and muskrats, but also true hamsters, vos, lemmings, which don't actually do that whole cliff thing, and all of the new world rats and mice. And given that they make a monopilletic group with the other two mouse families, and rat is just a name for big mice, I'm fine with including them all under the title mice. But just know that deer mice are closer to being hamsters or muskrats than they are to being true mice. And unless you're doing molecular analysis, again, it will be hard to distinguish these from members of the other two families we've discussed. They have three mers as far as I know always. So that would help in some instances. And they are often brown with white bellies. So that can help. But not all of them have white bellies. And they aren't the only family with white bellied or three molered representatives. In the year 1346, being in the Americas would be a good way to know that it wasn't either of the other two families, but you'd still be out of luck in the old world, and you wouldn't have YouTube or molecular phoggenetic analysis. Plus, there was the black death being carried by their European cousins, and you wouldn't even know that they were the cause. And if you claimed that you knew that it was from the rodents, you'd probably be burned at the stake. So, it's probably better now, even if you have a harder time distinguishing families of mice. This is definitely one of the best times in history to be a human, especially a phlogeneticist.

But I do have some bad news because the closest relatives of all of the mice that we've discussed so far are the family kellis, the mouse-like hamsters of the Middle East, which would be fine if we were discussing hamsters, but they aren't hamsters at all. Hamsters are in the family chet. Nothing in the families we have discussed so far is less related to hamsters than are the mousel-like hamsters, which are arguably mice. They're certainly mouse form rodents. So, hamsterlike mice would work for me, but they aren't very hamsterlike at all. If anything, they're gerbalike mice. I guess they were once thought to be hamsters based on the shape of their mers. And that really shows why we need molecular phoggenetics. You can get so focused on the feature that you think is most important that you can ignore that basically nothing else about this family is hamsterlike in the slightest. Not to mention that before genetic analysis, we thought there was only one species. That said, there are still fewer than a dozen described species of gerbilike mice alive today. So, they're a bit of a living fossil, but they all look like fuzzy tailed mice with hamsterish molers. And these four families together make up the caid u miroidoida meaning true mice. So what we've discussed so far all fall into the caid true mice. And while the genus moose might be the truest of the true mice. Everything from gerbles to hamsters to true rats to a whole bunch of other things that we call rats to muskrats and mouselike hamsters which certifiably are not hamsters. But all of these things are true mice.

But what about these or these? These are not part of the umoida, but they are still part of the super family meoidia and that means mice. So while they aren't part of the genus moose, the true mice or the ymoroida, which literally means true mice, we have at least two more families of mice at least. And the mice most closely related to the four families of true mice are the mice of the family spel from Eurasia and parts of Africa. The 37 species of zokores, bamboo rats, blind, and African mole rats. And before we get too far, if you are like most animal nerds, you have probably heard of naked mole rats. They're super cool rodents and they're from Africa. But guess what? They're not African mole rats. Though, I would say that an argument can be made that African mole rats aren't true mole rats and that naked mole rats may be true mole rats. But there isn't a rodent less related to African mole rats than naked mole rats. So, naked mole rats from Africa aren't African mole rats. They aren't true rats. And while rat at this point generally means large mouse, they aren't that either. Though they are almost certainly the strangest of all mammals, so we will get to them, but and not right now. Spolacids, unlike naked mole rats, are mice, though admittedly not true mice. They are primarily fossoral, meaning subterranean mice. And while we're on the subject of upsetting things, I told you that this group includes zokors, bamboo rats, blind mole rats, and African mole rats. And one of these four groups digs with big front legs like a mole. Guess which one? Yep, not the mole rats. Why would a mole rat dig like a mole? It's the zokor. So, the most molelike of all of the relatives of blind and African mole rats are, of course, not the blind or African mole rats, [laughter] and they're also not related to actual mole rats. But there are some conspicuous similarities between most of the members of the Spolac and the true mole rats. And one of those similarities would be that other than the moleike zokors, they tend to chew through the soil instead of claw their way through. This means that they use their incizers to dig, which could have some rather conspicuous downsides. I mean, if you bite through the soil all day, then you would end up with a big mouthful of soil. But they don't because like their extremely distant nude cousins, their insizers protrude out of their mouth and they can bite while keeping their mouths closed. Hence, no dirt. As a group, they also have small ears and eyes. These features are the least pronounced in the bamboo rats, which spend the most time above ground, and the most pronounced in the blind mole rats, which have some conspicuous similarities to snakes. Namely, their eyes are covered with skin, and they have no external ears. Though, I'm not sure if there is an ear opening under all that fur. They also lack tails, which snakes do have tails, but they're small. These guys don't have tails at all. They're just well they're weird. Though none of the spolacids have a tail more than half the length of their bodies. So short tails are not weird in this family except for the zokor. Spolacids tend to have very short legs. And in general you can probably distinguish them from any other mice. But there is one more family of mice. The mice least related to the other five families are the three species of pygmy and spiny door mice of the family platantomy from India, China, and Vietnam, which aren't dormice, >> but you said never. >> I know what I said. >> They're called doormice because they look like door mice, which are related to squirrels and mountain beavers, not mice. We'll get to them in a minute. But these are the only mice called dorm mice. You can tell that they aren't dormice because they only have three teeth behind their diastmas. Good luck spotting that. Or you can sequence their genes and see where they fit into the fogyny of rodents. But they are the only dorm mice that are actually mice. So that's the end of the mice, right?

Well, the super family moridia is within a larger cate that includes three more families. Those other three families are in a single cate, a super family called dipodia, which is a word that has nothing to do with mice. So, what are these families? Well, there's the family dipot today, the jerboas. And man, if you've been looking for a new favorite rodent, I think I found you a winner. What a delightful creature. There are around 33 species found in the hot deserts of northern Africa and Asia. And they tend to be big eared, long-legged bipeedal little rodents with huge long tails. They look a little bit like mini kangaroos except they're much more erratic in their hopping style. And of course, they aren't marsupials. And look at that skeleton. I would love a Halloween skeleton jerboa. And more than anything, it's just nice that we have finally moved out of the mice. So, uh, what else is in this clay? Well, the closest relatives of the jerboas, the family zapot, the 11 species of jumping mice. Take it through. Okay. The 11 species of jumping mice of North America and China. a funny distribution that we discussed in our video about crocodilians. As you can also see this pattern with alligators and paddlefish and loads of other animals and plants. This pattern doesn't make much sense given how far apart North America and China are, but it actually makes a great deal of sense. Jumping mice really do look like mice, though they tend to have four cheek teeth. So, that can be used to distinguish them from mice or other mice depending on if we're considering these and jerboas to be mice as well. But like jerboas, they are fantastic jumpers. In fact, if you startle a jumping mouse, it is likely to leap up to about 3 m in a single bound, which has got to be terrifying. So, jeroboas are most closely related to animals that look like mice and he can leap about >> 3 meters at a time. Jumping mice. But there is one more member of the clay. The family smith the 19 or so species of birch mice for crying out loud. Obviously, this video is already getting pretty long. There are almost 6,000 species of mammals and about 40% of them are just rodents. So, I knew that we might not cover all of them in one video, but I promised myself that I would at least get out of the mice. And while the three families in the dipodoidia are the hagfish of mice, it's hard to make a case that they are clearly not mice. Even jerboas really are just bouncy stilt mice. So, we can't end with the birch mice, but birch mice are in Europe and Asia. They look like mice. They might be mice, uh, like the rest of the dipoidia. They're awesome jumpers and have long back legs just like their cousins. And now I pray we are finished talking about mice because mice are great, but at some point you want to talk about something that looks different from a mouse with regard to more than just longer jumping legs and an extra cheek tooth. You know what I mean? And I have great news because we have finally escaped from the clay myomorpha, the mouse form rodents. And now we're moving into the clay most closely related to the mouse form rodents, the castoramorpha. And as someone who speaks Spanish fairly well, I know that this means beaver form rodents. And while we did run into at least one mouse that looked a heck of a lot like a beaver, I like to believe that we are finally in the clear. And of the three families of beaver form rodents, the family least related to the other two is the family castor, the beavers. So beavers are the hagfish of beaver form rodents. A bit reminiscent of the kopformms, don't you think? Today there are only two species of beavers, though there used to be giant beavers. And even modern beavers are pretty darn huge. They have webbed feet and scaly tails and overall look like muskrats. giant flat tailed muskrats with four or five top cheek teeth and four on the bottom. They are notorious for building waterhouses out of logs and sticks and for cutting those trees down themselves with their giant incizers. But that paddle tail is really what gives them away. Though that wouldn't help you if you just found a skeleton cuz the skeleton looks like an R O us skeleton like the biggest mouse you ever saw. But I don't want to talk about mice.

Let's instead talk about the two families most closely related to beavers. Geomiaday and heteromiaday. The pocket gophers and the kangaroo rats and kangaroo mites. Are you kidding me? Are beavers just giant paddletailed water mice? Okay, so pocket gophers the family geomiaday. [snorts] There are about 40 species in North and Central America. These are true gophers, though there are some squirrels that are often called gophers. So, you can say pocket gophers if you want to be clear which ones you're referring to. Or you can call them geomiads if you want to confuse everyone but your most hardcore rodent fan friends, which you might have given that you're watching this video. And you might lose those friends if you start calling beavers giant paddletailed water mice. But, you know, it might start a fun conversation, so I can't tell you not to do it. Pocket gophers get that name because of their large cheek pouches that can be used to store food. This is something that they have in common with hamsters and jumping mice. Though you wouldn't confuse them with either as they live primarily underground, have small eyes and ears, and overall look more like bamboo rats. You remember bamboo rats? You wouldn't confuse them with one though, as bamboo rats come from the other side of the world. However, their closest relatives, the roughly 60 species of kangaroo rats, kangaroo mice, pocket mice, and spiny pocket mice in the family heteromiaday, also have cheek pouches, and they live above ground. They're honestly some of the coolest animals on the planet. They're also found in the Americas, and with their location relative to the Earth's surface and the side of the planet, coupled with their cheek pouches, you shouldn't confuse them with anything else. Though, they do spend considerable time in burrows. They just have large eyes, relatively large ears, and long tails that keep you from confusing them with pocket gophers. In general, they have short forlims and long kangaroo-like hind limbs. And their tails are often tufted and used for balance while bounding. I love them, but I still don't feel like I've broken free of the mice. Obviously, I have not.

So, I'm going to try one more time. I'm going to step back just a little bit more because there is a whole other caid that is the most closely related caid to everything that we've discussed so far and that would be the clay skurorpha the squirrel form rodents their closest relatives are all of the families we've discussed so far but I have never thought of a squirrel as being a mouse so I think we should be in the clear unless of course you were paying attention earlier in this video in which case you will be filled with existential dread So, squirrel form rodents, there are three families, and one of the three families are the squirrels. Squirrels aren't even the hagfish of squirrel form rodents. And they're such a cool family that they're going to need their own videos so that we can dive even deeper because I have loved squirrels, especially flying squirrels and chipmunks, for as long as I can remember. I had a whole wall with chipmunk pictures growing up. I love them. But the family skira day also includes things like ground squirrels, prairie dogs, and marmets, which are the only live animals I saw in a classroom during my entire degree in zoologology, which is quite lame. Somehow, they found a way to suck all of the fun out of one of the coolest subjects on the planet. All I ever saw was a hibernating marmet, or as you now know them, giant squirrel popsicles. Squirrels are found in the Americas, Africa, Europe, and Asia, and thanks to humans, Australia as well. There are around 300 total species, which is why they need their own video, plus how much I love them.

Their closest relatives are the single species of mountain beavers of the family apploant from western North America, mostly just the West Coast. A species as poorly named as Rocky Mountain oysters, which is particularly ironic since they don't have a scrotum. But I don't know who was walking around on the West Coast, saw an animal that looked like a pocket gopher, and went, "Is that a beaver?" I mean, it has tiny eyes and ears and a tiny little tail. They're not big. Whoever it was must have only known about one rodent, but they aren't beavers. Nobody would mistake one for a beaver. And they aren't closely related to beavers either. They're the hagfish of squirrels. And other than squirrels, their closest relatives are these, the family glar, the 33 or so species of, and you better brace yourself if you forgot what I said earlier, dorm mice. These are the true dormice of Africa, Asia, and Europe, which means that we still aren't out of the mice. But I don't buy it. I mean, their closest relatives are squirrels and the world's least beaverly false beaver. And they look like their closest relatives are squirrels. If anything, they look like possums. Not to be confused

With opossums. Just because they're small, that doesn't mean they're mice. So, I say we've done it. We're free. And we're not quite done with the rodents.

We still have another amazing, huge, diverse clade to cover. The clade Hyraorpha, which could be called the rodents that definitely aren't mice. But this clade includes some really awesome things, like this, and this, and this. So, I'm pretty excited to get to talk with you about all of them.

I will start by saying that there is a lot of work to be done with regards to the phylogenetics of this group. So, it has taken me many months to create a phylogeny that I feel comfortable sharing with you. This is the best I can do. That said, this first group is a nightmare, not only for me but for phylogeneticists in general. They have a lot of similarities to members of the mouse clade that we discussed last time, as well as to members of this clade, and their position often changes. But it seems that this clade, Hyracoidea, belongs here, closer to capybaras than to true mice. The thing is that not only is the placement of this clade debatable, but also whether or not all three families in this clade actually belong together. It's a train wreck. So, I'm going to start with them. And you know that they're clearly rodents, but after that, just know that we don't have much certainty where they belong. But the good news is that they're stinking rad. I love these guys.

And they are the African families Pedetidae, the spring hares. Anomaluridae, the scaly-tailed flying squirrels that aren't squirrels, nor do they fly. They're also called flying mice, though if this is where they fit, they aren't mice either, and they still don't fly, but we'll get to that. And Zenobiidae, the Cameroon scaly-tail. Of the three, the one that seems to be most distantly related to the other two are the spring hares of the family Pedetidae. But go ahead and take that with a Spinosaurus-sized grain of salt. But wherever they go phylogenetically, spring hares are amazing. They are totally Africa's response to kangaroos. Though I can say with great confidence that spring hares are not closely related to kangaroos or wallabies, nor are they very closely related to actual hares, which are not rodents at all, but being lagomorphs, at least are much [clears throat] more closely related to spring hares than are any marsupials.

But just look at them. They're wonderful. Today, the family is represented by just two species: the East African spring hare and the South African spring hare. In general, spring hares are nocturnal, little herbivores with long ears, bushy tails, and big hopping legs. They spend the day down in burrows, so nighttime is really the only good time to see one. And they fluoresce under UV light like scorpions. So, you could potentially go blacklighting for them if you're ever in South or East Africa in the night, looking for one of the coolest rodents anywhere on the planet. I'm a little bummed that I didn't see one on my recent trip to South Africa. Of course, I did see some pretty insane stuff, so I really can't complain. We'll have some videos about that very soon. It was nuts. I have to go back to Africa someday. And for no other reason than to see these, the only extant member of the family Zenobiidae, the Cameroon scaly-tail, also called the flightless scaly-tail squirrel, which is not a squirrel. We have some confusion about where these guys go, but I don't think anybody thinks that they're squirrels. And unless you're talking about bats, it's safe to assume that if you're talking about a mammal, any mammal, [snorts] then it doesn't fly. But you will be able to see why they added the clarification when we discuss their closest relatives.

So, this is a flightless mammal that isn't a squirrel, but looks enough like one that they are sometimes called squirrels, and yet simultaneously have a scaly tail, which is something that I associate with rats much more than squirrels. So, how can I have a squirrel tail and a rat tail at the same time? Like this. It says, "Hey, let's have a tail." And we'll have it start out looking like a rat tail, but less than a third of the way down, let's have it turn into a big, bushy squirrel-like tail. That's how the bottom of the unfluffy region of the tail is not only unfluffy, but also covered in scales that seem to help give scaly tails extra grip on the trees. This footage of scaly-tails in the wild is somewhat remarkable, as the scientific community recently went 20 years without describing a new specimen. There are only 14 in museums, period. And no documented observations of them alive in the scientific literature. So, this is pretty special. Most of what we know of them, we know from the study of these 14 dead specimens. Like true squirrels, but unlike spring hares, they only have four toes on their front feet, five on the back, giving them a total of 18 toes, just like squirrels and spring hares, which have five on the front and four on each of their bouncy legs. The same number as kangaroos, though none of them are fused together as they are in macropods and other diprotodonts. But if you're in the eastern part of central Africa and you see a squirrel-like creature with a naked tail base and no patagium connecting its legs like you might see on a sugar glider, flying squirrel, or flying lemur, then you are a very lucky person. However, in most parts of central Africa, especially in the west, if you see a squirrel-like creature with a partially scaly tail, it's probably something else. These tail scales seem to help these guys hold on to smooth bark, as the trees in much of central Africa are not nearly as rough as trees in many other parts of the world and are thus hard to hold on to with claws. But if you see something that fits this description, it is likely to be one of the closest relatives of the scaly-tails, one of the six species in the family Anomaluridae, the scaly-tailed flying squirrels, which don't fly. But like sugar gliders, flying lemurs, and true flying squirrels, which also don't fly, they have a patagium, a flap of skin connecting their front and hind legs, which allows them to fall with style, like Buzz Lightyear. There are four extant lineages of mammals that glide like this, because being able to jump out of a tree, survive, and land on another tree is often handy if you live in a tree. Mammals aren't even the only ones doing it. There are flying snakes, flying frogs, and flying lizards as well, which also don't fly, but fall with style. But if you find a gliding mammal in Africa, this is what it is. Oh, and they don't fluoresce. I don't bring that up just because they're potential relatives; the spring hares do, but also because flying squirrels, true flying squirrels, do as well. And we don't know why non-gliding squirrels don't. But whatever has driven fluorescence in flying squirrels has not done so in these relatives, or at least potentially close relatives of fluorescent spring hares. Go figure. But what cool creatures? And in Africa, you won't confuse them with anything else.

All of the remaining rodents fall into two clades. One of them very small, and the other huge. So, I'll start with that small clade because it only includes two families, and then we'll really dig in. Those two families are the families Thryonomyidae, the cane rats, and the family Diatomyidae, the Laotian rock rat. I think we actually discussed cane rats in our most recent list of 10 animals I didn't know existed, and that is why I love making these videos. It's so fun to discover rat animals that I didn't know about before. Well, I've only known about cane rats for a few months now, and I'm a fan. There are only five species, all found in northern Africa, so it's not that shocking that they've flown under my radar. Uniquely among the groups that we've discussed so far, they have only 16 total toes with four on each foot, none anywhere else. On their hind feet, the middle two toes have comb-like structures on them that are the source of the common name comb rat, as well as the name of the family, which means comb finger. Living in the deserts of northern Africa, water is scarce in their world. So, they don't drink. Like many other desert rodents, they get enough water from their diet and metabolism to fulfill their water needs. They tend to be tannish in color and have a shape similar to a pika. Though the ears are very different, very unique. Unlike the Mickey Mouse ears of pikas, which aren't actually rodents, gundi ears sit much lower on the head, kind of right behind the eye. The outside of the pinna is the same color as the rest of the animal, but the inside is much darker in color and almost looks like a second pair of eyes. I can't think of a better way to describe it than that. They look like a pika and a jumping spider had a baby. Like pikas, they have generally small tails, though I think there is at least one species with a rather long tail.

And the closest relatives of gundis are these, the Laotian rock rat, the only extant member of the family Diatomyidae, which, as their name would suggest, are from Southeast Asia. And when they were discovered, that was the first evidence of any of the family Diatomyidae existing in the last 11 million years. Fossils of small rodents are not that common. They don't fossilize well, but it was still pretty surprising to find one alive. Just as surprising as finding the first coelacanth. Both were found in markets for sale as food. So, if you're hoping that non-avian dinosaurs are still alive, that's where I'd look, because this world is still full of wonders yet to be discovered in food markets. Should you be in the mountains of Laos, what you should look for is a dark gray rodent with the face of a rat and the tail of a chinchilla. They have a bit of a Roman nose, which may be even more prominent than it is on many rats. Their whole head is rather large for their body, but they are about the size of a squirrel. I really like them.

And that gets us to the meat and potatoes of the remaining rodents. All of which fall into two main clades, and again, one is much larger than the other. So, we will start small, though this clade has as many families as the two that we have discussed so far today combined. And that clade is called the Myomorpha, which I know is one of the clades that I have been most excited to talk about, at least since we discussed blind mole rats. Myomorpha, as with all the other groups that we've discussed in this lineage, is primarily African. As we discussed in our video on the Afrotheria, Africa was until not that long ago an island. As such, it has a considerable number of unique species on it, even many that are morphologically similar to very distantly related groups that fill similar ecological roles in other parts of the world.

And of all the myomorphs, the family that appears to be the most distantly related to the others is the family Hystricidae, the 11 species of Old World porcupines. Not to be confused with the porcupines of the New World. Those aren't even in this African clade. Remember what I said about convergent evolution being a big thing in Africa? Well, it turns out that being a pointy rodent makes a lot of sense. It can be dangerous being a rodent. And the world is a lot less dangerous if you're spiky as heck. At least for you. Obviously, not for your enemies. And don't worry, we will get to the American porcupine soon enough. Just not in this clade. Africa, no longer being an island, is no longer the sole home of these Old World porcupines. They are now found up into Asia and Europe and have even made their way to the island of Flores, which means that Komodo dragons have probably wound up on the wrong side of one of these porcupines. I am, by training, an evolutionary ecologist. I study specifically life history evolution, and I can tell you that the life history of Old World porcupines clearly demonstrates that having pointed hairs of pain is working really well for them because they have a very different life history from that of most rodents and different in a way that suggests that not much kills them because most rodents hit maturity very quickly and have a lot of small offspring. Both of these are signs of organisms in which being killed by a predator is very likely for both juveniles and adults. Well, Old World porcupines generally don't become adults until they're about 2 years old. That's about the same time as for a leopard. Rats, for comparison, take about 6 weeks to hit maturity. And once old porcupines hit maturity, they only produce between one and two offspring per year. Rats can have upwards of a hundred in a year. This is not the life history of an animal that gets killed often by predators. This is about the birth rate of lions, which tend to be protected by a pride of lions. Being pointy works. They also tend to be pretty social and stick together in family groups. This is one thing that differentiates them from New World porcupines. They also tend to be much more terrestrial. Their quills are clustered and not interspersed with non-quill hairs, and they do not detach the quills. That is. Though they can shake them to produce a formidable rattling noise. Additionally, they lack the long, often prehensile tails of New World porcupines. In most ways, they are very different creatures, but you don't want to sit on either of them. Oh, and just while we're on the subject of rear-facing quills of pain, the dinosaur Psittacosaurus had some really similar structures. So, this might not just be something that has happened multiple times in the rodents, but in other groups as well.

The remaining four myomorph families fall into two clades, each containing two families. One containing creatures that are called rats but look very little like rats, because again, "rat" basically just refers to any rodent that you feel like calling a rat. But the other clade contains two families of hideous monsters with teeth outside of their lips, both with and without hair. And I think I'll start with them because we've been waiting a long time to talk about them already. So, these are the families Bathyergidae, the mole-rats, or African mole-rats, and Heterocephalidae, the naked mole-rats, which are also from Africa, but naked. Neither of these families are closely related to the blind mole-rats that we discussed previously, though they do have a similar way of digging, since none of these animals called mole-rats dig in any way like moles. They don't dig like moles, or Africa's answers to moles, the Afrotherian golden moles, or Australia's answer to moles, the marsupial moles. They don't dig like any of those things, which all dig with huge forelimbs with giant claws. Nope. These guys don't really use their legs to dig at all. They chew through the dirt, which for normal rodents would mean a mouthful of dirt. But that isn't a problem if your giant incisors are outside of your lips. So handsome. They can be distinguished from their Eurasian doppelgangers by their distribution, which is exclusively in Africa south of the Sahara Desert. They also tend to be much more social. Some are even like ants and bees, something that you might be aware of in naked mole-rats, but that is also present in one of the species of dressed African mole-rats as well. Others are cooperative breeders, but are not fully eusocial. The roughly 20 species of African mole-rats can be distinguished from naked mole-rats by, you know, that fuzz that's all over their bodies. You know the stuff. I would definitely enjoy making a video about just these two families in the future.

But we still have a lot of ground to cover, like the final two more families which appear to be one another's closest living relatives. These would be the families Thryonomyidae, the cane rats, and the two species of cane rats in the family Petromuridae. Now, "cane rat" is African. At least "dassie" is, and it means hyrax, which is funny because I was just in South Africa where they speak Afrikaans and where they have both dassies and hyraxes. In fact, I saw a bunch of hyraxes up close, which was pretty exciting. Hyraxes are the closest extant terrestrial relatives to elephants, and at a glance, nobody would think that. But I don't know who is seeing dassie rats and mixing them up with hyraxes, other than that they are similar in color and both like to hang out on rocky outcroppings. Dassie rats have a big squirrel-like tail, though not as bushy, and hyraxes super do not like, super duper do not have long bushy tails. I mean, you might have a longer tail than a hyrax, but they probably look more like hyraxes than high-contrast Chinese bamboo bears look like pandas. So, I guess we'll let it slide. Though their overall color can vary, they tend to have yellowish snouts. Hyraxes, on the other hand, have big black noses. They're also much larger. So, from the front or the back, you shouldn't confuse them with rock-dwelling afrotherians. And they aren't found as far north or east as their closest relatives, the cane rats. Nor do they look like cane rats, which are much larger. In fact, they are the largest rodents in Africa other than porcupines. They're more similar in size, actually, to a hyrax, but have a square face like an Old World porcupine and a long tail, at least compared to a hyrax. And that tail is actually pretty naked, like that of a muskrat, which is probably the North American rodent that lives in the most similar way to cane rats, which are also semi-aquatic, though cane rats are probably more social than our muskrats.

And that gets us out of Africa because there was one lineage that made its way to the Americas and then went absolutely bonkers: the Caviomorpha. And this is probably the largest rodent clade that is also universally loved by humans. The Caviomorpha, the guinea pig-form mammals. And being a human myself, I love them. How could you not? This group includes not only the largest rodent alive today, but also the largest rodent known to have ever lived, Josephoartigasia monesi, which weighed at least a ton, possibly more than 2.5 tons. That's well more than a bison and one serious rodent. >> Firstly, what about the rodents of unusual size? >> I don't think they exist. Whereas their closest relatives are found primarily in the Old World, mostly Africa, Caviomorpha is a New World clade, principally found in South America with only limited success north of Mexico. As is the case with opossums being the only extant lineage of marsupials to have colonized the north after the Great American Interchange, you know, when North America and South America became connected for the first time. Well, only one extant lineage of caviomorph has done the same. Though there were North American capybaras until not that long ago, and they were bigger than modern capybaras. But even if they were alive today, it would still be safe to say that this is a principally South American lineage.

There are approximately 10 extant families in this clade, though the phylogenetic work is, as has been the case with most of the rodents, a bit of a train wreck. I have constructed the best phylogeny that I can, but keep your salt close at hand. You're likely to need it. It appears that the first caviomorphs came to South America around 40 million years ago, probably from Africa, based on their phylogenetic placement squarely in an African clade. After arriving, they quickly radiated, and most of the families that exist today were present by about 30 million years ago. This type of rapid radiation following an introduction is not all that uncommon, as many niches are likely available. All of these 10 or so families fall into two large clades: one with four families and the other with six. And since the smaller of the two clades includes actual guinea pigs, and this is the guinea pig-form rodent clade, I think it's appropriate to start there. Not to mention the fact that you have waited long enough to talk about New World porcupines, and they're in this clade as well, much more closely related to guinea pigs than they are to Old World porcupines, but still the family most distantly related to the other three, which together form a clade called the Cavioidea.

But let's start with the guinea pigs and work our way back to the porcupines. Despite being the namesake of the whole clade, the guinea pig family, Caviidae, is one of the smallest families of rodents in existence today. That is in terms of species, though not the smallest family that we'll talk about today. And when I say small, I mean this in terms of the number of species. They're only 19, not in terms of actual size. The largest living rodent on the planet is one of those 19. One of the two extant species of capybaras, which can weigh over 90 kilos, more than 200 lb. Also in this group are maras, which I adore, and a bunch of things generally called cavies, including guinea pigs. In general, this group is made up of relatively large, herbivorous rodents with large, box-shaped heads and tiny, often not visible tails. Due to the extinction of the North American capybara, this is today a nearly pure South American family. They only barely make it into Central America. They have four toes on each front foot, but only three on the hind feet, like an emu. They also produce rather few offspring for a rodent after relatively long gestation times: 150 days for a capybara.

The closest relatives of the caviids are the 14 or so species of agoutis and acouchis in the family Dasyproctidae. Like their closest relatives, they come from South and Central America and also seem to have four front toes and emu hind feet and tiny tails, though they are somewhat more gracile in shape. Other than the maras, caviids tend to be more stocky in build. And these guys have the more traditional rat or squirrel-shaped head, not the rectangular heads of their cousins, and much smaller ears than maras, which is probably the only caviid that you could potentially confuse for a dasyproctid. In general, despite their similarities, you shouldn't confuse the two families because of the differences in body and especially head shape. If you were going to confuse another family with Caviidae, it would probably be their next closest relatives, the two species of pacas in the family Cuniculidae, as they are also stocky with more square heads. Though I would argue that pacas look more like baby tapirs than they do like caviids. I mean, just look at that coloration. They just lack the trunk in the front and the junk in the rear, and the rodents. Like tapirs, they're found in South and Central America and even make their way into Mexico, though there aren't any in Asia. So, that's a point for their ungulate doppelgangers. Very different from their closest relatives, pacas have five toes on each hind foot, though still only four on the front. But like their closest relatives, they mostly just walk on three hind toes. So, you can probably see how we went from the more normal rodent toe arrangement to the emu feet that we saw before. Like tapirs and some of their closest relatives like capybaras, pacas spend considerable time in and around water. They can stay submerged for as long as about 15 minutes, which is an eternity for a rodent. Though they also live in burrows, and I don't think tapirs tend to do that. And instead of a proboscis, they have resonance chambers in their cheeks to enable them to make a loud, scary growling noise.

So, these are the three families that make up the Cavioidea, which, you know, brings us finally to the New World porcupines of the family Erethizontidae, which includes a total of about 19 species of pokey rodents that are not closely related to the Old World pokey rodents in the family Hystricidae that [snorts] we discussed previously. There are a lot of subtle differences between the two families, like the fact that their molars are rooted and they have a complete clavicle or collar bone, but they also tend to have a long prehensile tail, unlike Old World porcupines, which is handy, kind of literally, because they're much more arboreal. Their quills also tend to be dispersed amongst other hairs rather than all over the body, are barbed, and often detach when they become embedded in the flesh of an attacker. All of this is very different from the Old World porcupines. But like their well-defended Old World doppelgangers, they still have the life history of an animal that doesn't get killed much. They generally only have one offspring per year, and they just nurse for sometimes over 200 days. That's getting pretty close to human sorts of numbers, not rat kinds of numbers. The North American porcupine clearly has established itself in North America, where it persists to this day. But as has been the case with their closest relatives, all of the rest are found farther south. And while this isn't present in the North American porcupine, which has a bit of a caviid face, most of them have a fun, almost pig-like snout, including the one that tried to become my best friend in Peru. >> Look at this porcupine. >> Oh my gosh, that is... shine your light on it. >> Ever. >> Hi. >> Contrary to popular belief, they do not throw their spines. >> This is an arboreal porcupine. Hey, buddy. >> Hi. Oh, that is the coolest thing. >> Touch him. >> So bad. [laughter] We got to be careful for this car hitting him here. Okay, here. Should I try driving that way a little? >> Oh, he's going to come to you. >> Hey, buddy. Got to get off the road in a second here. Wow. >> When you're spiky enough, you just don't need to be afraid of much.

And that gets us to the end of the smaller clade of caviomorphs. And honestly, pretty much all of the things that we knew had to be in this clade, which makes you wonder what we have in this other clade. But I can tell you at least one family that you likely know exists right now: this one, the family Chinchillidae. And since this larger clade of caviomorphs itself includes two large clades, I will start with the one that includes something that we already know about: chinchillas. And then we will get to all of their closest relatives. So, check this out. What the heck is that? My sister-in-law Jessica sent me a photo of one of these a few years ago when she was in Peru. What the heck is it? I mean, it looks basically like a rabbit, but that tail clearly isn't right. Well, turns out that this is a viscacha, the closest relatives of the chinchillas. Specifically, this one is a northern viscacha, one of the four species of mountain viscachas. There is also one species of plains viscacha. But since mountain viscachas are more closely related to chinchillas than they are to plains viscachas, uh, that would mean that chinchillas are viscachas too. At least if viscacha is to be understood to be a natural monophyletic group. But there are seven total species in the family Chinchillidae, composed of chinchillas and other viscachas. Unlike rabbits, they are rodents and have long tails. But they do have large ears that are in most cases somewhat long and rabbit-like. They are about rabbit-sized and have longer back legs than front legs. They all live in South America, with all but the plains viscacha living in the Andes Mountains, where I used to live, though I never saw one. It's okay. I saw vicuñas, flamingos, cool amphibians, lizards, and more. Much more alive than I ever saw living in the Atacama Desert. But never one of these. Their success in the mountains is likely highly related to their extremely dense fur. Most have four toes on the front and four on the back, though plains viscachas have only three on the back. And they all have long, bushy tails. They're all herbivores and live in large colonies, which is probably how we should keep chinchillas.

The closest relatives of chinchillas and other viscachas are these, the 10 species of chinchilla rats of the family Abrocomidae, which are neither chinchillas nor rats. Though we probably know by now that "rat" is just a name for any relatively large but not too large rodent that you feel like calling a rat. And they are the only other family in the clade Chinchilloidea. The hagfish of chinchillas, if you will, at least if all the scotias are chinchillas. And they look pretty much like if a chinchilla and a rat had a baby. So, chinchilla rat seems rather appropriate. Though there is some debate as to whether or not they are actually sister to the Chinchillidae. They may belong to the other clade that we're going to discuss later, Octodontoidea, but we'll get to them soon enough. I'm just glad you still have your salt with you. They certainly do look like chinchillas, some more than others. And they also live in the Andes Mountains. So, if that similarity is just due to convergence, it does make sense. Similar or in this case, same habitats can result in similar forms. In some cases, they look more like chinchillas than do viscachas. So, even if they are closely related, it is still probably convergence that accounts for their uncannily similar appearance. That is, viscachas have lost the ancestral chinchilla appearance. Generally, chinchilla rats are smaller than chinchillas, but the largest chinchilla rats are larger than the smallest chinchillas. They have somewhat longer faces, five hind toes instead of four, and tails that are much less bushy than those of chinchillas. On the middle three of those five back toes, they have stiff hairs that they use like little combs. So, a long-faced subfluffy-tailed five-digited comb tower is a chinchilla rat. A short-faced fluffy-tailed quadratto is a chinchilla.

But if chinchilla rats turn out not to be the closest relatives of chinchillas and other viscachas, then it would be these, the pakarana, the sole extant member of the family Dinomyidae, a group that once included bison-sized mega-rodents and that you would probably only confuse with a paca. You remember the family Cuniculidae? It's a pretty strong resemblance. Heck, the word pakarana means "false paca" in the Tupi language. Paca is also a Tupi word. These guys are also found in many of the same regions of northwestern South America. So, we have another false baby tapir rodent in the same place where you might find the other false baby tapir rodents and actual baby tapirs. It also lacks the junk and the trunk of tapirs. And it has a long tail. Honestly, to me, it looks like a cross between an African porcupine and a wombat with the tail of an opossum and the color of a baby tapir. And while way smaller than a bison, at 15 kilos, they are a rodent of considerable size, to be sure. Unlike pacas, pakaranas tend to be social, hanging out in groups of four or five, all sitting up to eat their food like prairie dogs and having only four toes on each foot, where the pacas have five on the hind feet. But I would go with the tail, the bulk, and the buddies to tell them apart.

And that brings us to the final rodent clade. And the most disturbing clade it is indeed. I mean, if you remember this, and this, well, now take a look at this. If I told you that these three animals all form a clade, would anyone be shocked? No. But you already know that this and this are not that closely related to one another, because muskrats are closely related to things like deer mice, and beavers are closely related to pocket gophers. Well, there isn't a rodent more distantly related to this or this than is this. And there is no rodent more distantly related to a pocket gopher than is this. And there is no rodent more distantly related to a deer mouse than is this. But those creatures are all closely related to one another. They are all members of the infuriating clade Octodontoidea.

Okay, so let's start off with these false beavers. That is a nutria. It's one of somewhere around 85 species of what are called spiny rats in the family Echimyidae, making it the most speciose family we have encountered since we left the mice behind. This family is mostly found in South America, but they do get up into Central America and the West Indies. Nutrias obviously look like beavers or or muskrats, but they aren't. But most of this family looks like rats. Of course, if they are rats to be monophyletic, all rodents at this point would need to be rats. But you know what rats are? Any rodent that isn't too big or too small that I feel like calling a rat. Though some, like the Desmodontinae hutia, look like a woodchuck and a wombat had a baby and gave it a rat tail. This is a crazy group that probably needs its own video eventually. They're called spiny rats because they have some spiky hairs. Like they're considering that porcupine path that the rodents have already embraced fully at least twice. But in the meantime, they're playing with other defenses like the popular salamander and squamate ability to autotomize their tails. [snorts] Yeah, they can drop their tails. Did I not say that they were an upsetting clade? And they don't grow back. So, they got that move from the crested geckos, it would seem. For the most part, they are either arboreal and rat-like or fossorial and gopher-like. Obviously, with the occasional semi-aquatic beaver-like form. In many ways, they seem to be South America's answer to the mice, though maybe not just this family alone, but rather the whole troubling Octodontoidea.

The last two families in this nightmare are both more closely related to one another than they are to the spiny rats. These would be the families Octodontidae and Tenreidae. And I'll start with the Tenreidae, better known as tuco-tucos, because they name themselves like Pokémon. They're called tuco-tucos because they say "tuc tuc" all the time. And there are something like 70 species of them in South America, filling essentially the same ecological niche as pocket gophers in North America, and looking a heck of a lot like a pocket gopher, just without the cheek pouches and maybe with slightly larger eyes. But in general, if you see a pocket gopher, but you're in South America, this is probably what it is. What you won't know is how many chromosomes it has. Chimpanzees have 24 pairs of chromosomes, whereas humans have only 23. It's pretty clear that our shared ancestors had 24 as well, but humans have 23 due to a fusion of two of the chromosomes into a single giant chromosome. It's pretty cool. It's also possible for chromosomes to split, be duplicated, or even deleted. And all of these things can change the chromosome number. Two go from five to 35 chromosome pairs, which is insane. Though it's pretty similar in foxes, and not all dogs have bones. And since we normally talk a lot about skeletons in October, what do you say we talk about that this October?

But there is one more family here left to discuss. The final rodent family, the 14 species of viscacha rats, churos, rock rats, and degus of the family Octodontidae of South America. The name Octodontidae refers to the figure-eight shaped wear pattern that their teeth often get. But let's just face it. They look like rats and mice with short, round little chinchilla faces. And one of them has 51 pairs of chromosomes. Others have only 19. And I really wish I understood more about how chromosomal numbers can fluctuate so rapidly in some lineages. So please let me know what you know about that.

But that gets us to the end of the rodents already and in fact out of the entire Ur-clade, which brings us to the Laurasiatheria, which admittedly does not include the pinnacle of creation, but it does include pangolins, porpoises, and mammals that can actually fly, like flying foxes, and real foxes that don't fly, as well as some fake foxes that also don't fly, because, uh, well, not all foxes are foxes. Foxes, especially flying foxes. And this is a clade that includes a lot of small groups that we have never discussed before, like the true insectivores of the clade Eulipotyphla, the clade most distantly related to the other members of the Laurasiatheria. I refer to them as true insectivores because in the past we lumped a lot of other groups in with them. Things like tree shrews and colugos, even though colugos are herbivores. Not to mention a whole lot of Afrotherians that we will discuss here shortly. But today, there are just four families in this clade. And the family most distantly related to the other three appears to be the family Solenodontidae. The two species of solenodons, pipe teeth of Cuba and Hispaniola. They're weird-looking creatures with very long, cartilaginous snouts, long, hairless tails, naked feet, and tiny eyes. They actually look strikingly like rodents. >> Wesley, what about the rodents of unusual size? >> I don't think they exist. >> And if you get a look at the teeth of rodents, you will notice that they aren't rodents. If you get a good look at the teeth of solenodons, which look a lot more like those of our rodents, you might worry even more for Wesley after his bite. They're venomous. Solenodon means "pipe teeth" because they have a groove in their lower incisors through which their venomous saliva flows. If those were what they appear to be, rodents, then Wesley might not be out of the woods just yet, or the fire swamp, as it were. But that would be a rodent, as they are actually fairly large for this clade. But they're not that big. Without including their tail, they are just under a third of a meter long, 11 to 13 inches, and weigh around or just under a kilo, like 1.5 to 2.2 lb. That would also be a rodent, but a solenodon of usual size. Same initialism, different meaning.

After solenodons, the family next most distantly related to the other two is the family Talpidae, the 45 or so species of true moles, including shrew moles and the highly aquatic desmans, which we discussed previously, or the golden moles that are more closely related to manatees. They're not even close to being in this group, but the resemblance is uncanny. Unlike the fake moles of Africa and Australia, which are found near the equator or in the southern hemisphere, true moles are an entirely northern hemisphere phenomenon, ranging across North America and Eurasia. So, by location alone, there should never be a reason to mix them up with their southerly doppelgangers. They also tend to have dark fur, which further distinguishes them from fake moles. But, they do have rather tube-shaped bodies with hairless snouts and are fairly small, with the largest weighing only a little over half a kilo, about 550 grams, and the smallest being only about 12 grams. So, some are really small. That's the size of a AAA battery, though it's almost 7 times the size of the smallest member of the next family that we will discuss, which is the smallest mammal of all, but we'll get to them in a moment. In all cases, talpids have small eyes and poor vision with tiny or non-existent ear pinnae. Like swimming platypuses, they rely heavily on touch to navigate the world and locate food. Some, like the generously named star-nosed mole, have elaborate sensory structures to amplify their ability to feel out even the smallest of prey. But let's be honest though, Cthulhu-ed mole would have been a lot more accurate. I've never seen a star that looks like a pair of flesh-colored sea anemones, but I guess maybe I just need to get out more. And while we're on the subject of penises, most of them have a backwards-facing penis and no scrotum. One more feature that clearly distinguishes them from all of the pseudomoles is that they have five clawed toes on their forefoot, which are enlarged for digging in most of the family or webbed for swimming in the desmans.

Their closest relatives are the two remaining families in the Eulipotyphla: the nearly 400 species of true shrews of the family Soricidae, which are not to be confused with things like the tree shrews that we just discussed, otter shrews, elephant shrews, marsupial shrews, or any of the other things that are called shrews that aren't part of this family, and the 26 species of hedgehogs and the moon rat of the family Erinaceidae. Also have afrotherian doppelgangers. Look, Afrotheria is a ride, just embrace it. But I promised that I would talk next about the shrews because the smallest of all mammals just happens to be one: the Etruscan shrew. It weighs 1.8 grams when fully grown. That's considerably less than the weight of a dime, which is almost 2.3 grams. So, a really obese one might weigh as much as a dime. Of course, it's hard to become obese with the metabolism of a shrew. Even the largest shrew is only about 100 grams. That's less than a stick of butter. So, they're never very large. But they are found on every continent except Antarctica and Australia. So, they're doing great. Shrews, not unlike moles, have small eyes and poor vision. This is one way to tell them apart from many of the false shrews like elephant shrews and tree shrews, as well as mice, which have very different teeth, but at a glance can look a lot like a shrew. I mentioned that they have fast metabolisms. They do, as in many need to eat between half and twice their body weight in food every day just to stay alive. Some need to regularly enter torpor, like hummingbirds, just to make it through periods in which they can't eat for a few hours. Because they have to eat so much and because they are not rodents or lagomorphs with continuously growing teeth, their teeth need to be super strong; they are reinforced with iron, which gives them an often reddish appearance, but is not found in species with lower metabolisms. Iron teeth are reserved for those that need to eat the most. And speaking of teeth, many species have grooved teeth that channel venom into the bite wounds of their prey. So, this is yet another venomous mammal. And in some cases, that venom is highly potent. I've never heard of any human fatalities attributed to shrew envenomation, but they could easily kill mammals larger than a shrew. Some estimates of certain shrew venoms suggest that the venom from one bite could kill something like 200 mice. That's pretty nuts. But venom and a lightning-fast metabolism aren't their only weird features. Being blind as bats, in fact, blinder than some, and fairly closely related to bats, as we will discuss soon, and with excellent hearing, it maybe isn't so crazy that they can echolocate just to navigate. They aren't as precise as bats, but they can echolocate, as can their cousins, the solenodons, which are also venomous. There is only one other group of land mammals with this ability, and they look like this. And knowing that hedgehogs are the closest relatives of the shrews, that probably adds up. The only problem is that that isn't a hedgehog. It's a tenrec, an afrotherian. But that probably doesn't shock you by now. Actual hedgehogs don't seem to have this ability, but they do have a very similar look. And the funny thing is that while tenrecs are afrotherians, you don't find them in mainland Africa, but hedgehogs are found in Africa as well as Eurasia, with the moon rat coming from Southeast Asia. So, they have a convergent afrotherian, but if you find an animal that looks like a hedgehog in mainland Africa, then it's probably a hedgehog. Though they're closely related to shrews, moon rats are probably the only ones that you could potentially confuse with shrews. Hedgehogs are all spiky with larger eyes and short tails. And most of them are larger than shrews, generally with the smallest ones being over 40 grams. So, smaller than some shrews, but getting to be as much as about 1.4 kilos, which is over 3 lb. And that biggest one is the species of moon rat. So, even if it looks the most like a shrew, it is way, way bigger than any shrew. Like 14 times the size of the largest shrew. Honestly, if you showed one to me out of context, I I mean, I might think it was an opossum of some sort. Of course, on closer inspection, there are a lot of differences between opossums and moon rats, but at a glance, and being in Southeast Asia should be a dead giveaway. Not to mention the fact that they uh smell powerfully of ammonia. That's a difference you can probably feel in your nostrils.

The next most distantly related clade within the Laurasiatheria is one of the strangest and most successful clades of all. In fact, almost a quarter of all mammalian species are part of this clade: the bats, which is where we're going to start part two, which you can watch right now.