The shapes of fossilized teeth from 65.9 million-year-old, squirrel-like creatures suggest that the branch of the tree of life that gave rise to us humans and other primates flowered while dinosaurs still walked the earth.
That’s the claim coming from a team of 10 researchers across the U.S., including biologists at Seattle’s Burke Museum and the University of Washington.
In a study published by Royal Society Open Science, the team lays out evidence that an ancient group of primates known as plesiadapiforms must have emerged before the mass-extinction event that killed off the dinosaurs. (Technically, modern-day birds are considered the descendants of dinosaurs, but that’s another story.)
The evidence comes from an analysis of tooth fossils that were unearthed in the Hell Creek area of northeastern Montana. The fossils are all associated with a plesiadapiform genus known as Purgatorius. However, the researchers say some of the teeth have the characteristics of a previously known species, Purgatorius janisae, while others came from a newly named species called Purgatorius mckeeveri.
The team estimated the age of the teeth at 65.9 million years. That’s a mere 105,000 to 139,000 years after the Cretaceous-Paleogene extinction event. When the researchers wound back the evolutionary clock, they determined that the older species from which those two different species sprang must have existed before the mass extinction.
Thus, the teeth add to evidence that the earliest members of the primate family — a tribe that includes present-day humans, apes, monkeys and lemurs — were among the survivors of a Cretaceous catastrophe.
“It’s mind-blowing to think of our earliest archaic primate ancestors — 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,” one of the study’s leaders, Gregory Wilson Mantilla of UW’s Burke Museum, said in a news release.
Brody Hovatter, a UW graduate student, also played a role in the study.
“This was a really cool study to be part of, particularly because it provides further evidence that the earliest primates originated before the extinction of non-avian dinosaurs,” Hovatter said. “They became highly abundant within a million years of that extinction.”
The study’s other collaborators include study co-leader Stephen Chester of Brooklyn College and the City University of New York’s Graduate Center; William Clemens of the University of California Museum of Paleontology; Jason Moore and Wade Mans of the University of New Mexico; Courtney Sprain of the University of Florida and UC-Berkeley; William Mitchell of Minnesota IT Services; Roland Mundil of the Berkeley Geochronology Center; and Paul Renne of UC-Berkeley.