66 million years ago, an animal about the
size of a rat was hunting down insects and searching for fruit among the evergreen leaves
of ancient relatives of the magnolia. With a tiny, narrow face and a long bushy
tail, it probably looked a bit like a squirrel. But it wasn’t. Its name was Purgatorius, and it may be one
of the world’s earliest primates - an ancient relative of ours. But maybe the most surprising thing about
Purgatorius is where it was found: eastern Montana, not far from where I am now. And another species of Purgatorius has been
found in Saskatchewan, Canada. So, let that sink in: Early primates not only
lived in North America -- our primate family tree actually originated here! Fossil primates have also been found from
central Alberta to southern Texas, and from California to Mississippi. So, if primates really did evolve in North
America, what happened to those early relatives of ours? Why don’t we have monkeys and tarsiers and
lemurs wandering around the U.S. and Canada today? (Man, how cool would that be?) Well, the short answer is: North America was
once a lot warmer and wetter, offering an ideal habitat for early primates. But it didn’t stay that way for long, and
eventually they all disappeared. But the longer answer is that primates would
eventually return to their home continent. They just went … the very long way around. Today, non-human primates live on all the
continents except Australia and Antarctica, and the ones that still live in North America
are limited to Mexico and Central America. No matter how and where they live, though,
today’s primates have some things in common ... with the occasional exception. We all have big, forward-facing eyes that
are either completely surrounded by a ring of bone or walled off by a bony plate. And, for the most part, we have all nails
instead of claws on our fingers and toes. These traits, along with a few others, define
the taxonomic order of Primates, which includes humans, apes, monkeys, tarsiers, lemurs, and
bushbabies, to name just a few. But once you start looking at the fossil record,
you’ll see that our primate ancestors looked pretty different. For example, Purgatorius is a member of a
group known as the plesiadapiforms. They appeared around 66 million years ago
and the last of them vanished about 37 million years ago. Many scientists consider plesiadapiforms to
be the earliest primates, but there are some traits that set them apart from the likes
of you and me. For one thing, most of them didn’t have
nails - they had claws. And while they did have big eyes like modern
primates do, their eyes weren’t as close together, which meant that they didn’t have
quite the same level of depth perception. Still, they did have bumpy, lumpy teeth to
help crush fruit, like many primates do. And they had long fingers and toes that were
good for grasping onto branches and tree trunks, with mobile ankle joints to help them hang
on. So it’s these traits that led many scientists
to classify pleisadapiforms as the earliest primates. And! Like so many primates today, plesiadapiforms
mostly lived in warm, wet forests. ah but here’s the thing. 66 million years ago, those rainforests stretched
far from the equator -- all the way up into the Arctic circle. And these vast rainforests and warm climates
allowed lots of different groups of primates to thrive throughout North America. To wit! By the start of the Eocene Epoch about 56
million years ago, North America was also home to omomyiforms, a group of tarsier-like
primates, and adapiforms, which were more lemur-like. And these little primates were really diverse. Several species often lived in the same area,
like the three species of omomyiforms found in the Friar’s formation of Southern California. But being a rainforest specialist only works
well when there’s ... lots of rainforest – and those aren’t as common in North
America as they used to be. Why? Well because, around 50 million years ago, way
on the other side of the world, big changes were underway. A chunk of the Earth’s crust known as the
Indian plate rammed into Eurasia, starting the process that would eventually form the
Himalayas. And the weathering of these growing mountains
helped pull carbon dioxide out of the air, which cooled the planet dramatically – nearly
12 degrees Celsius by about 35 million years ago. And as temperatures changed, tropical environments
retreated back toward the equator. So by the time the Eocene Epoch was over,
North America no longer had the right habitat for primates. Now, you’d think that this was the end of
the story (for North America’s primates). You’d think! But back in the 1960s, paleontologists found
a handful of teeth and a jaw on the Pine Ridge Indian Reservation in South Dakota. And these teeth were tiny – the biggest
of them was less than 4 millimeters long. But they shared traits with our teeth; they
were short-crowned, and lumpy, built for crushing rather than slicing. For a while, scientists weren’t even sure
the owner of these teeth was a primate. Because, while some of the teeth were really
similar to ours, they had some differences, too. The ones in back were smaller than the ones
in the front, and they had a few bumps that were unique. But, when more, similar fossils were found
in, this time in Nebraska and Oregon, experts reached the conclusion that this animal was,
in fact, a primate - just a really strange one. And here’s the thing: It lived 29 million
years ago – almost 10 million years after every other primate in North America went
extinct. So how was this primate able to survive, when
others didn’t? The answer, unfortunately, isn’t clear. After all, we only have a handful of teeth. But those teeth do tell us a few things: First, they tell us that this animal was bigger
than many other late North American primates, about the size of a small house cat, as opposed
to a rat. And getting bigger is a pretty common evolutionary
response to cooling temperatures, so maybe that could’ve helped it endure the change
in climate. Another interesting insight is that these
teeth were found in what used to be an open woodland, or a grassland with trees scattered
around. That might not sound like a very primate-friendly
place, but there are arboreal primates today that live in similar environments – like
bushbabies, which live in open woodlands in Africa. And the bumpy nature of the teeth also tells
us that this little primate was probably mostly eating fruit, instead of the bushbaby’s
diet of tree gum, some insects, and maybe a little bit of fruit. And this could’ve helped it survive longer,
too. Because! It turns out that primates that eat fruit,
at least without destroying the seeds, tend to be more evolutionarily successful – because
they spread their preferred food via their poop. For example, during the end of the Eocene
in Africa, primates that relied primarily on leaves started to become extinct, but the
ones that ate fruit survived. And that might be because primates that specialize
in eating leaves don’t contribute as much to the spread of their preferred food source. So it’s possible that this last North American
primate made a decent living in a much drier, less forgiving forest environment than its
ancestors did, because it brought the trees it needed with it, spreading its own food
through its poop. Which is a phrase I never thought I’d say. But whatever led to its initial success didn’t
last forever. The climate continued to change, and as North
America became drier, grasslands kept spreading. While some primates in Africa have been able
to adapt to a grassland environment, it appears that their North American counterpart simply
couldn’t. As a result, 26 million years ago, it went
extinct, and primates disappeared from all of North America. But only for a while. In 2016, a handful of primate teeth were found
in the Panama canal basin. And they belonged to Panamacebus, a member
of a family of monkeys that was only found in South America at the time. But the teeth were about 21 million years
old – when North and South America were separated by ocean. So how did Panamacebus get to North America? Scientists suspect that it rafted there, maybe
during or after a storm, when it rode on a mat of plant material to the new continent. It may sound strange, but for now it’s the
best way to explain how primates could’ve crossed the ocean. And even though Panamacebus managed to make
it to Panama, it never made it any farther north – possibly because it, like so many
others, was attached to living in the rainforest. And it didn’t last, either Meanwhile! The monkeys found in South America today are
most closely related to the monkeys that live in Africa. And though it’s a bit contentious, their
arrival in South America is theorized to be the result of storm rafting, too! So, what about the monkeys that live in Mexico
and Central America today? Where’d they come from? Well! Genetic evidence suggests that they arrived
from South America around 4 million years ago, after North and South America had become
mostly attached. And, like Panamacebus, they never made farther
north than the rainforests. So, you could say that the descendents of
North America’s first primates only recently made it back to their original home continent. Their evolutionary journey took them around
the world, from their likely origins in Montana and Canada at the start of the Cenozoic Era,
to Asia and Africa in the Eocene Epoch, where they probably diversified into the ancestors
of the major groups of primates alive today. Eventually they rafted from Africa back to
the Western Hemisphere, maybe between 37 million and 34 million years ago , where they evolved
into all the families of primates that live in South America today. And while all of that was going on? Those primates that stayed in North America
disappeared - the victims of a changing environment. It would take 22 million years for primates
to really make it back to the North American mainland, after North and South America reconnected
just a few million years ago. It was… quite a trip. With the return of monkeys to Central America,
the North American continent had native primates again. And then, of course, we showed up. And we’re adapted to thrive in a whole bunch
of different environments, not just rainforests. So it seems like this latest group of primates
is probably here to stay. I mean...I hope so? Thanks for watching Eons, which is produced
for PBS by Complexly. If you’re a US citizen and you want to have
a voice in your government, check out How To Vote In Every State. The rules for voting are different depending
on where you live, so Complexly has made a whole series of videos explaining how to vote
in each state, as well as some advice for special cases like territories and overseas
voters. And this year Complexly has also put together
a guide for first-time voters with help from our friends at MediaWise to help you navigate
everything from your news diet, to political ads, to money in politics. Check it out at youtube.com/howtovoteineverystate So if this episode got you thinking, “how
did we get from Purgatorius to us?”, check out our episode: Your Place In The Primate
Family Tree to learn more about human evolution. Also high fives to our fellow primates and
this month’s Eontologists: Lucan Curtis-Mahoney, Sean Dennis, Jake Hart, Jon Davison Ng, Patrick
Seifert, and Steve! You can join them by supporting us at patreon.com/eons. And as always thank you for joining me today
in the Konstantin Haase studio. If you like what we do here, Subscribe at
youtube.com/eons!
