Who was our ancestor when the dinosaurs died?

66 million years ago, on a bright spring morning, when the flowers were in bloom, an asteroid roughly 12 km wide, traveling at 72,000 km an hour, smashed into what is now Mexico, causing an explosion billions of times more powerful than the bombs dropped on Japan. Every animal within 180 km was instantly vaporized. A shock wave blasted across the land for 1500 km. The earth shook with magnitude 11 earthquakes. Rock rained down on the hapless dinosaurs, triggering worldwide wildfires. Ash filled the sky, creating a nuclear winter that lasted years. Photosynthesis shut down. An entire ecosystem collapsed. A diverse world full of incredible beasts came to an end. All the non-avian dinosaurs dead. The giant winged terasaurs dead. Marine monsters like Mosasaurus dead. 75% of all life on Earth was dead.

This is going to sound a little bit strange, but I kind of love thinking about this day when the dinosaurs died, even though it's like probably one of the worst days in the history of the Earth. You know, it's become almost meditative for me. Basically, whenever I think like all my problems are so bad, blah blah blah, I'm so stressed, what have you, I just remember that at any moment in time, an asteroid could smash into the Earth. And yeah, it just makes my problem seem small. It's like that meme of the two guys on the bus. I'm definitely the one looking on the sunny side.

But this day, this day, this moment in time has become more than just a a psychological tool of mine. I've kind of become obsessed with it because obviously life did survive. It's all around me. And also, we're here, too. And I can't help but think, you know, who was our ancestor that survived this moment? What fossils do we have? What do we know about this time? And do these fossils give us any clues as as to how maybe we did survive this this absolute apocalypse, this incredible asteroid impact? So, that's that's what this video is about. Who was our ancestor when the dinosaurs died?

Okay. So, if we want to find our like super ancient ancestors way before even the evolution of humans, we have to understand what makes us who we are, what traits define us, and and what a paleontologist would look for in the fossil record. You're probably all aware that humans are primates. We're in the order of primates. Our closest relatives are chimpanzees and gorillas, orangutans. We're all apes. Apes are dry-nosed primates, the haplerines, alongside various monkeys and baboons, even tarsers. And more distantly than that, we're related to lemurs, the strepzerines, the wetnosed primates. But what is it that unites us all? What makes us all primates? A lot of the traits that align primates together, everything from you and me to a chimpanzeee to a calopus monkey and even tars or lemurs are some of the features of both our cranium know in our skull and our really a lot in our hands and feet.

That's Andrew Schwarz. He studies the early origins of primates. He kind of started this whole obsession of mine by emailing me ages ago about this topic. I think we need a skull here. It's an orangutan skull. A replica, of course. One really defining trait is that, of course, we have these large forward-facing eyes and larger than average brains. Obviously, humans have big brains, but all primates have have a larger than average brain. Interesting shaped skull here on the orangutan. The other feature that really defines our face is called the post orbital bar. Basically, our eye socket is fully encased in bone. There's no gap around here. In other animals, like you see this uh this guy right here, it's an opening. In a lot of other mammals, it's an opening.

When we look at our dentition, our dentition, our teeth are generally actually pretty um they're they're not super derived. They're they have we have a lot of these ancestral conditions that the earliest, you know, euththerian, the earliest placental mammal would have had. We don't have scissor-like teeth that carnivorous animals have. We don't have these really tall hips teeth like horses or other grazers. We have lowcrowned broadbased kind of bulbous posterior teeth to consume our food.

When we look at postranial features, of course, we have diverging thumbs and big toes. Although since humans evolved to walk upright, obviously our toe is not diverged anymore, but you can see it in early hominin fossils. We had a diverged big toe. We have fleshy pads on our hands and feet for grabbing. And crucially, we have nails. We have fingernails instead of claws.

We have flattened distal flanges. So the last bones in our fingers and toes are flat rather than kind of curved like a dog's claw or cat's claw where then there's a big nail on top of it. And that's something that is also a very unique trait to primates. Some primates have actually reevolved claws, but the ancestral primate would have had nails on most, if not all of their digits.

Now, you might be thinking, how do we know that all these traits are evidence of shared ancestry and and didn't just evolve independently? An example of convergent evolution. I was wondering that, too. Is there any way in particular that we can tell that all of these traits come from a common ancestor and aren't an example of convergent evolution, for example?

That's a good question and we do need to ask that because when we look at some of our close relatives that we know aren't primates, we see some of these traits reappear. This is the skull of the tree shrew and it actually has a post-orbital bar. But we think that is an example of convergent evolution. The reason that we're fairly confident that these traits, you know, the post-orbital bar or the converging large orbits or the nails or the divergent hexock and big thumb are are a synapomorphy are a derived shared trait among all primates is because when we look through the great diversity, the hundreds of species of primates that are alive today or in the fossil record, we see that they all have this trait. All of these features, the forward- facing eyes, the grasping hands, the diverging toes, this all suggests we were clambering up and down these trees. We were up in the trees somewhere. And so I really wanted to know when do we start to see these features appear in the fossil record. Who the earliest primates?

That asteroid that wiped out the dinosaurs is obviously an accident. Quirk of fate could not be avoided. But today, so many species are under threat and it's entirely avoidable. It's it's driven by us. It's caused by us. And to do nothing is is really a choice. And We have to do more to protect nature, basically, which is why I'm super proud to be partnered with Planet Wild. They are a community-based nature protection organization. Think of it as crowdfunding for helping nature. Every month, their 20,000 members pick a new project to help restore forests, protect the oceans, you know, help bring back endangered species. It's fully transparent. They document all their work here on YouTube. So, every month you can see what your contribution has achieved. I know this is cliche, but truly, ever since I've had children, I really think a lot about the world we're leaving for them. You know, kids are so into animals. They absolutely love nature, and I just want them to live in a world that is thriving. Many of the species we're discussing today lived in North America, and one of Planet Wild's recent missions has been about restoring the American Serenity, supporting species like prairie dogs and pong horns and the American bison. If you want to join a growing community that helps nature, consider Planet Wild. outside of the sponsorship I've joined. They're not paying me to say that. Of course, I would never say that uh if it wasn't true. And the first 100 people to sign up using the code Stefan 2, I believe their first month is paid for by me somehow. Just click the description, scan the QR code, and yeah, and the best thing is in the next 30 days, you'll already see how you've helped here on YouTube. Big shout out to Planet Wild.

The earliest true primates appear around 56 million years ago during a time period called the PETM or Paleoe thermal maximum. This was a really warm time in Earth's history. The polar regions were almost certainly free of ice. Instead, the Arctic was home to subtropical swamps and palm trees, home to crocodiles like Borealis sucus that lurked in waters as far north as Saskatchewan. The earliest ancestors of horses appear in the fossil record for the first time. They were just the size of cats. Little cat-sized horses. Wish we still had some of those. Some animals were, of course, pretty small, but others were huge. In South America, giant >> terra birds >> hunted for prey. It was almost the return of the dinosaurs. For marine life though it seems to have been a challenging time.

So the Paleocene Eocene thermal maximum or the PETM is this relatively short period right at 56 million years ago where the global climate becomes very hot about 5 to 8° C over a very brief span. So the warming was probably caused by the release of methane from the ocean floor. Various hypotheses for that we could go into. And this warming may have taken place only over a few thousand a few tens of thousands of years.

The PETM was one of the most rapid periods of of global warming in all of Earth's history. As far as we're aware, except for now we're now currently warming faster than the PETM, which is a worry. I'm definitely worried that I was able to go to the beach in January. If you look where I am now, there's barely any snow on the ground. Usually, this place would be 6 8t deep in snow right now on the side of Mount Hood. There's barely any. But it's during this PETM that we see the first true primates appear in the fossil record. The first up primates as they're called. This fossil here is one of the best pictures I could get of an early primate. It's called Aribbus from China. See this poor little guy curled over? It's absolutely tiny, less than 1 ounce, whatever that is in metric. Fortunately, the feet were preserved and the flat bones sort of shield shaped fanges suggest that this animal had nails and was a primate like us. Of course, you can see other adaptations for climbing there, too. We have another interesting primate specimen called Cantus. Another really interesting one where we have a few fossils is called Talhardina. It has some adaptations for climbing, but also a true orbital bar suggesting it was a primate just like us. This specimen here is from China, but they have been found in Belgium, as far south as Mississippi. Quite a widespread early primate. Basically all across the northern hemisphere, and that's probably because during the PETM, this was where the forests were. This was where the primates could live. It gets very aid, very dry and doesn't return to uh preetm, you know, late paleosene temperatures and weather conditions for about 200,000 years. We have this ele these, you know, very elevated temperatures and low rainfall conditions.

There's a a problem though when we're thinking about the hunt for these early primates. There is a problem. Cantius, Talhardina, Arusibbus, these primates that live 56 million years ago, they're already quite derived. Paleontologists believe Tile Hardina and Arcibus were probably already on the side of the family tree that became Tarsas. They were dry-nosed primates like us. Canas is probably an early wet-nosed primate, a strepzerine. This is the first big divide in the primate order between Haplarines and Strepzer, which means that these can't really have been the first primate. So, we know that the earliest primate, their most recent common ancestor, lived considerably earlier than that.

Finding these primates further back in time than the PETM is is very difficult for a couple of reasons, though. First, all these different features that that primates have, they didn't necessarily evolve all at once. You might find fossils that have some features of primates, but some features that primates don't have. And so, figuring out their relationship to later species is is really, really tricky. The second problem is that it seems we were just tiny. It seems we were just absolutely tiny. Look at the scale bar for some of these early primates. We're talking millimeters here. Look at the picture of this tile hardiness jawbone compared to this man's fingers. Small small creatures like the size of squirrels and whatnot. Tiny animals. And that just makes it hard for them to become fossils. Fossilization is a is a rare process, right? Like an animal has to be buried quickly but gently and then it has to survive until our time period and then we have to find the right soil to to get at it before it's destroyed by erosion or something. It's incredibly hard. It's incredibly difficult and that's you know it's difficult when you're talking about a giant animal like T-Rex or Triceratops, never mind a tiny little mouse, basically a mouse-sized animal. It's so hard. It's so tricky. Um, but nevertheless, we do have some cool examples that take us back to that moment 66 million years ago, to that time of the asteroid impact.

Before the PETM, one group of animals we see with primateike traits are the plesiaforms. Plesiaforms actually means near adapforms. Adapoforms were an early family of primates. So, they're near primates basically.

So, the plesapoforms are our closest cousins. They're about as close to primates as you could be without being true primates.

And today they're not really seen as their own separate family. They're more of a series of successive species with some actually being very closely related to primates, some being a little less closely related to primates, some being even less, and so on. The plesiaforms don't have all the features associated with true primates. They don't have particularly large brains. They don't have true orbital bars. They have claws. Some of them are even really strange.

One has adaptations to be kind of a a primate like woodpecker.

This is the one that Andrew was talking about there. I think it's called chairomyoides. A plesia dappaform but with enormous front teeth almost maybe like a beaver. Something like that. Something, you know, they had to be using these teeth for something. Maybe ripping apart bark and trees, things like that. Even though there are some weird and wonderful plesia dappaforms, they do show some similarities to primates. They definitely have adaptations for climbing. One specific specimen called Carpest Simpsoni seems to have had a divergent big toe with a nail on the end. Classic primate stuff. And for much of our story prior to the PETM, we're really only dealing with the plesforms. We don't have primates prior to the PETM, but something like a plesform. Something very similar to it would have given rise to our lineage. All the primates.

The oldest plesform ever found takes us about as close as we can possibly get to the extinction of the dinosaurs. Realistically, this here, you probably can't even see that cuz it's so dark, but this here is Hell Creek, an offshoot of the Missouri River in eastern Montana. A rugged landscape for sure, but one of the best places to hunt for dinosaurs or anything else alive at that time. It's in amongst these dry rolling hills that paleontologists found a little critter they called Purgatorius because it was found on the side of a purgatory hill. Very fire and brimstone kind of name. very appropriate for a little creature that might have lived through an asteroid impact. It's believed to be an early form or or ancestor to to plesia dappa forms. And because Purgatorius has a lot of these primate like traits, um a lot of its back teeth, it's posterior dentition is similar to plesappforms and primates. And it has um ankle bones actually that are very similar to primate ankle bones, which are really good at grasping onto, you know, large diameter objects. So this was an aroreal. This is an animal that's climbing up and living in trees. Purgatorius is of course not a true primate, but it's the earliest example we have of perhaps a stem primate. You know, the kind of creature that might have evolved into primates. It was something like Purgatorius. Closest animal alive today that might resemble Purgatorus is probably the closest relative of primates, a tree shrew >> and belugas.

Peratorus was probably quite similar to this little chap. The really incredible part though are the age of these fossils. They were excavated from layers that date to just 100,000 years after the asteroid impact, right back to the time of the dinosaurs. Basically, this tiny creature, just 15 cm big, weighing no more than 100 g, it was almost certainly the kind of creature that survived the impact. They lived through this terrible moment in Earth's history, this tiny little furry chap. And seemingly Purgatorius or something like Purgatorius evolved into primates. It's always subject to change of course, but with the evidence we have at the minute, this is as close as we can get. This is basically our ancestor that survived the asteroid impact.

Chatting whilst I had the opportunity to chat to Andrew though, I wanted to know one final thing. Do we have any idea what was driving our evolution? What kind of habitat our earliest primates evolved in? As we mentioned before, all the features of of primates suggest that we were adapted for life up in these trees in this incredibly complicated 3D world. But but but but that might not be the only key. That might not be the only thing going on. Something else was evolving alongside us that might have been the sort of the driving force behind our evolution and our our divergence from our closest relatives. The angioperm co-evolution hypothesis puts that rather than being um you know visual predation being the main driver of primate evolution. It was the co-evolution of angioperms these are flowering plants. These are fruing plants with primates. Primates evolved to take the niche of uh consuming fruits and flowers.

It seems crazy to imagine a world without many flowering plants. That's so different to our time. Um, but in the grand evolution of thing, flowering plants didn't take off until until quite late, quite recently. Although they first evolved over 100 million years ago, they wouldn't be the dominant form of plant life until around 85 million years ago. Now, obviously, that's about 20 million years before our little Purgatorius existed. Here's the interesting thing. ignoring the fossil record. According to genetic estimates, the primate order split from our closest relatives around 80 million years ago. Like we kind of evolved alongside these flowers, our tiny furry bodies and and perhaps our ability to live in dens or holes in trees probably helped us survive the, you know, terrible winters that must have followed that asteroid strike. We didn't need to eat tons of stuff. You know, we could we're kind of generalist. We could nibble on an insect. We could nibble on a fruit. We can nibble on a flower. Anything to keep us warm, keep us going. The dinosaurs, these big beasts at the top of the food chain, they needed so much more. They needed so much more food to keep them going. A T-Rex can't just nibble a couple of ants and be okay.

So, basically, that's what science knows at the moment. That's kind of the limit of our scientific knowledge. True primates seemingly emerged in the heat of the PETM as North America split off from Europe. For the 10 million years after the asteroid impact, the plesiodapaforms, the diverse group of kind of semi primate like animals were roaming the world, little tiny purgatorious or something like that was making it through the nuclear winter that followed, you know, with little furry bodies. And they were probably doing it by chewing on bugs and eating flowers and berries and stuff like that. You know, you may owe everything. We may owe everything, everything, absolutely everything to the evolution of flowers, a fairy body, and nibbling on an insect. Think about that, man. Think about that. Crazy. Crazy. We're flower people. We're really flower people. Thank you for watching. Doesn't that make you want to support conservation work? Honestly, we are a product of our ecosystem. Truly, we can't live without it. Go check out Planet Wild. If you're interested in supporting conservation work, you can see their work for yourself on YouTube. Go check out their work on the American Prairie, for example, if you want to see what they're up to. And yeah, stay tuned for the next one. Thank you so much.