Earliest Ancestor of Humans Lived With Dinosaurs

Fossils from the earliest primate group, the appropriately named Purgatorius found in Hell Creek, Montana, date to before the mass extinction 65 million years ago

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Shortly after the extinction of the dinosaurs, the earliest known archaic primates, such as the newly described species Purgatorius mckeeveri shown in the foreground, quickly set themselves apart from their competition -- like the archaic ungulate mammal on the forest floor -- by specializing in an omnivorous diet including fruit found up in the trees.
Illustration of Purgatorius, among the earliest archaic primates, which rose after the fall of the dinosaurs - and apparently began its road in their shadowCredit: Andrey Atuchin

The earliest primate of all lived with dinosaurs, a team of American researchers suggests, based on the discovery that at least two species of them were already running around about 100,000 years after the mass extinction that all but wiped out those terrible lizards. The little furry things almost certainly had to have evolved earlier, which means they lived with dinosaurs. Including the big ones.

It’s true that these archaic primates were more like an arboreal rat than a B movie actor armed with a time machine and a jeep. But it’s awesome to think that our ancestors, albeit extremely distant ones, were dodging T. rexes. Though to be honest, the archaic primates were so small T. rex couldn’t have used them for much except maybe to floss its teeth with their tails.

Yet dodging dinosaurs must have been terrifying, assuming this really did happen, and it seems it did. Fossil remains of at least two species of the appropriately-named Purgatorius found in Hell Creek, Montana, are estimated at 65.9 million years old. That’s 105,000 to 139,000 years after the Cretaceous extinction that did the dinosaurs in, explains a team of American researchers publishing in the journal Royal Society Open Science.

Based on the languid pace of evolution, the fact that there were at least two species of purgalicious primatoids by this time indicates they had emerged earlier. In other words, our ancestors (very distant) had emerged by the Late Cretaceous, says the team led by Gregory Wilson Mantilla of the University of Washington and Stephen Chester of Brooklyn College and the City University of New York. 

The study is based on analysis of several fossils of Purgatorius, the oldest member in the group of the earliest-known primates, which is known as plesiadapiforms.

High resolution CT scans of an assortment of fossilized teeth and jaw bones of Purgatorius.Credit: Gregory Wilson Mantilla/Stephen Chester

Most of the obvious plesiadapiforms disappeared during the Eocene epoch that ranged from about 34 million to 56 million years ago, but theoretically they didn’t go extinct because, well, you’re reading this. There is some argument how one got from Purgatorius in a tree to today’s crown primates, but evidently one did.

In fact, there were multiple species of Purgatorius, further supporting their emergence before the dinosaurian apocalypse. The team describes two Purgatoriuses in Hell’s Creek: Purgatorius janisae and a new species that the team named Purgatorius mckeeveri. It was named after Frank McKeever, among the first residents of the area where the fossils were discovered.

One hallmark of the primate set is fingernails instead of claws. The case of Purgatorius’ feet remains open and it’s depicted here with claws. But it may have already featured fingernails. Teilhardina, which thronged Asia and North America more than 56 million years ago, had flattened toe- and fingertips, indicating that it had nails, not claws.

Meanwhile, some primitive monkey types such as the owl monkey still have a “grooming” claw on one of their five digits instead of a fingernail; either it “regressed” or, based on archaic fossil monkeys with a similar mixed arrangement, the transition from claws to nails wasn’t entirely straightforward.

Anyway, the retained claw helps scratch flea bites and obtain lovely grubs living inside palm trees and that sort of thing. But fingernails may have become the norm because they were more helpful, or less intrusive, when grasping at branches. Long claws would get in the way.

Fingernails are also more useful at crushing lice one catches – go ahead, try it. It has even been suggested that archaic primates could afford to lose their claws because they had each other and would groom each other, ridding one another of parasites.

Baboon groomingCredit: Muhammad Mahdi Karim

Anyway, there they were: archaic primates who somehow survived the asteroid that really did slam into Mexico and really did wipe out all dinosaurs except for birds. “They were some of the first mammals to diversify in this new post-mass-extinction world,” Wilson Mantilla says.

The team suggests that proto-monkeys of the type were one of the oldest known placental groups, and were key to the evolutionary radiation of placentals and the Cretaceous-Palaeogene recovery of animal life on land. Within about a million years after the asteroid strike, these primitive primates dominated the arboreal omnivore and frugivore niche.

In other words, they were running riot, “taking advantage of the fruits and insects up in the forest canopy,” as Wilson Mantilla puts it. But lo, we would not remain denizens of the treetops.

The progression from these innocent tree-ratty things to us is not linear. After about 60 million years it led to the emergence of a hyper-carnivorous land animal we call Homo erectus. That erectus, according to a new hypothesis of human evolution published by Tel Aviv University researchers, ate its way to the virtual extinction of the big animals it preferred. Then our ancestors had to develop the smarts to hunt smaller, more elusive animals.

And now various elements, including Israeli companies, are trying to bring us back 65 million years to eschew steak and bacon, and eat bugs for protein. Given the damage the Homo sapiens line has done to animal species the world wide, it isn’t the worst idea.