Fossils hint earliest primates lived with dinosaurs

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. (Credit: Andrey Atuchin/UW)

Researchers have discovered the earliest-known fossil evidence of primates.

The researchers analyzed several fossils of Purgatorius, the oldest genus in a group of the earliest-known primates called plesiadapiforms. These ancient mammals were small-bodied and ate specialized diets of insects and fruits that varied by species.

These newly described specimens are central to understanding primate ancestry and paint a picture of how life on land recovered after the Cretaceous-Paleogene extinction event 66 million years ago that wiped out all dinosaurs—except for birds—and led to the rise of mammals.

The team analyzed fossilized teeth found in the Hell Creek area of northeastern Montana. The fossils, now part of the collections at the University of California Museum of Paleontology, are estimated to be 65.9 million years old, about 105,000 to 139,000 years after the mass extinction event.

Several teeth, including some connected to jaw bones
High resolution CT scans of an assortment of fossilized teeth and jaw bones of Purgatorius. (Credit: Gregory Wilson Mantilla/Stephen Chester)

Based on the age of the fossils, the team estimates that the ancestor of all primates—including plesiadapiforms and today’s primates such as lemurs, monkeys, and apes—likely emerged by the Late Cretaceous and lived alongside large dinosaurs.

“It’s mind blowing to think of our earliest archaic primate ancestors,” says Gregory Wilson Mantilla, a professor of biology at the University of Washington and curator of vertebrate paleontology at the Burke Museum of Natural History & Culture. “They were some of the first mammals to diversify in this new post-mass extinction world, taking advantage of the fruits and insects up in the forest canopy.”

The fossils include two species of Purgatorius: Purgatorius janisae and a new species described by the team named Purgatorius mckeeveri. Three of the found teeth found have distinct features compared to any previously known Purgatorius species and led to the description of the new species.

Purgatorius mckeeveri is named after Frank McKeever, who was among the first residents of the area where the fossils were discovered, and also the family of John and Cathy McKeever, who have since supported the field work where scientists discovered the oldest specimen of this new species.

“This was a really cool study to be a part of, particularly because it provides further evidence that the earliest primates originated before the extinction of non-avian dinosaurs,” says coauthor Brody Hovatter, a graduate student in Earth and space sciences. “They became highly abundant within a million years after that extinction.”

“This discovery is exciting because it represents the oldest dated occurrence of archaic primates in the fossil record,” says co-lead author Stephen Chester of Brooklyn College and the City University of New York. “It adds to our understanding of how the earliest primates separated themselves from their competitors following the demise of the dinosaurs.”

The late William Clemens, professor emeritus at the University of California, Berkeley and former director of the UC Museum of Paleontology was a coauthor of the study, published in the journal Royal Society Open Science. Additional coauthors are from the University of New Mexico, the University of Florida, Minnesota IT Services, the Berkeley Geochronology Center, and UC Berkeley.

The National Science Foundation, the UC Museum of Paleontology, the Myhrvold and Havranek Charitable Family Fund, the University of Washington, the City University of New York, and the Leakey Foundation supported the work.

Source: University of Washington