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-ᴇxᴛɪɴᴄᴛion event that ᴋɪʟʟed off the dinosaurs. (Technically, modern-day birds are considered the descᴇɴᴅants of dinosaurs, but that’s another story.)
The teeth and upper and lower jawbones, from a genus of mammals known as Purgatorius — the oldest genus in a group of now ᴇxᴛɪɴᴄᴛ early primates called plesiadapiforms — were collected over the past two decades from the Hell Creek region of northeastern Montana, south and east of Fort Peck Reservoir. The area is known for its T. rex and Triceratops ғᴏssɪʟs, but also for some of the earliest ғᴏssɪʟ mammals.
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 ᴇxᴛɪɴᴄᴛion 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 ᴇxᴛɪɴᴄᴛion.
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.
Gregory Wilson Mantilla, a former UC Berkeley Ph.D. candidate who is now professor of biology at the University of Washington (UW) and curator of vertebrate paleontology at the university’s Burke Museum in Seattle, said: “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 ᴇxᴛɪɴᴄᴛion world — taking advantage of the fruits and insects up in the forest canopy.”
The new discovery is central to understanding primate ancestry and paints a picture of how life on land recovered after the Cretaceous–Paleogene ᴇxᴛɪɴᴄᴛion event that preceded the rise of mammals. Specifically, within 1 million years of their arrival in northeastern Montana, plesiadapiforms outstripped archaic ungulates — the ancestors of hoofed animals, like deer — in abundance, and dominated a key ecological niche: tree-dwelling mammals with an omnivorous and/or fruit-eating diet.
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 ᴇxᴛɪɴᴄᴛion of non-avian dinosaurs,” Hovatter said. “They became highly abundant within a million years of that ᴇxᴛɪɴᴄᴛion. It adds to our understanding of how the earliest primates separated themselves from their competitors following the ᴅᴇᴍɪsᴇ of the dinosaurs.”
The ғᴏssɪʟs were collected during annual trips to the Hell Creek area initiated by the late William Clemens, an expert on the mammals of the 86-million-year-long Mesozoic Era, which ᴇɴᴅed with the mass ᴇxᴛɪɴᴄᴛion. The ғᴏssɪʟs include two species of Purgatorius: Purgatorius janisae and a new species described by the team and named Purgatorius mckeeveri. Three of the teeth found have distinct features compared to any previously-known Purgatorius species and led to the description of the new species.