A formation famous for its production T. rex fossils have now provided the oldest evidence of primates in the fossil record, in what is hailed as an important discovery.
Jawbones and an assortment of teeth found in the Hell’s Creek Formation in northeastern Montana are the oldest primate fossils ever discovered, according to New Research published in Royal Society Open Science.
Dating from about 65.9 million years ago, these animals lived only 105,000 to 139,000 years after the extinction of the Cretaceous-Paleogene, with an asteroid wiping out most of the plant and animal species on Earth. The new paper was co-led by Gregory Wilson Mantilla from the University of Washington and Stephen Chester from Brooklyn College and the City University of New York.
“This is an important study because it documents the earliest primates ever discovered, pushing the dating of the oldest primates back to the earliest Paleocene, in addition to establishing greater diversity,” said Eric Sargis, a professor of anthropology at the University of Twente. Yale University. affiliated with the new study, said in an email.
Indeed, the age of these fossils is significant, as it suggests that the ancestor of all primates, both extinct and extant, lived during the Mesozoic Era, particularly the Late Cretaceous. Prior to this discovery, the oldest evidence of tribal or early primates in the fossil record dated from the first 300,000 to 500,000 years of the Paleocene (the era that followed the Mesozoic).
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The newly discovered teeth and jawbones belong to two different types: P. janisae and P. mckeeveriBoth types belong to Purgatorius, the oldest known genus associated with primates. Other members of this group include P. unio and P. ceratops, and they are all considered to be plesiadapiforms – a tribe of primates that includes Purgatorius and from which all modern primates such as monkeys, monkeys (including you) and lemurs are descended.
P. janisae was already known to paleontologists, but P. mckeeveri is a newly described species named in honor of a family that has supported fieldwork in this field. Three teeth with properties not seen before in Purgatorius let the scientists explain the discovery of a new species.
The team studied these extinct creatures by delving into a large collection of fossils at the University of California Museum of Paleontology, which houses the largest collection of P. janisae fossils. They also had epoxy casts from others Purgatorius fossils to work with, as well as enlarged 3D models printed from microCT scans. The team also used a technique called “geometric morphometry” to digitize features of fossils and compare them with other known species.
“This work was done with a large team that added diverse and critical skills to this research, from the geochronologists who could determine the age of these fossils to the geologists who could decipher how these fossils were deposited,” Mantilla said. in an email. “We could not have done this work without the help of generous colleagues from the museums where we worked [with] and the landowners in Garfield County Montana who allowed us to work on their land. It was a great team effort. “
Scientists do not yet know the exact timetable for the emergence of Purgatorius, but the “fact that there are two species” that appeared so soon after the mass extinction “implies that their ancestor predated the two descendants,” Mantilla wrote. It is increasingly likely that the ancestor of Plesiadapiforms “first arose in the Late Cretaceous rather than the Paleocene,” he said, meaning that the earliest proto-primates would have rubbed the elbows with the dinosaurs.
As for the predecessor of Purgatorius, that’s still a mystery. As Mantilla explained, some North American fossil species dating back to the late Cretaceous are proposed to be the ancestors of Purgatorius, including the ratty GypsonictopsIt is more likely that “we have not yet found the ancestor in the fossil record,” he added.
These tiny placental mammals looked very squirrel-like, but Purgatorius, like other plesiadapiforms, “share dental features with other primates,” Sargis said, adding that their teeth were “primate-like, not rodent-like.”
I asked Chester what makes a primate a primate, to which he responded:
This is a great question and a central issue for all researchers studying the origins of primates. Until we fully understand what makes a primate a primate, it is difficult to know when our primate ancestors diverged from other mammals. Many primates today have traits related to grabbing, jumping, a plant-based diet, improved vision and intelligence. However, we know from the fossil record that all of these traits did not evolve at exactly the same time. As paleontologists, we can trace this combination of traits to extinct primates from the earliest Eocene, about 56 million years ago. But if you go further back in time, to the earliest Paleocene, about 66 million years ago, it is clear that our earliest primate relatives such as Purgatorius had some, but not all, of these traits. Two major sets of features that evolved very early in primate evolution were skeletal features such as grasping hands and feet for tree life and dental features such as specialized molars for eating non-foliar plant products such as fruit. This combination of traits allowed our first primate relatives to stand out from their competition just after the demise of the dinosaurs.
As according to the new study, Purgatorius were among the first mammals to succeed in the Paleocene, which appeared “shortly after the catastrophe that wiped out non-avian dinosaurs,” explained Mantilla. “They had a few adjustments that allowed them to thrive in the aftermath of this disaster. First, they were arboreal – they spent most of their time in the trees – and second, they had teeth that allowed them to feed on fruits and insects. “
It seems these properties are allowed Purgatorius to “grow within a million years of the mass extinction and become an important part of the terrestrial ecosystem,” he added.
Mammals first appeared during the Late Triassic about 300 million years ago (we’ve been around for a while!). That primates were able to thrive after the extinction of non-avian dinosaurs is no great surprise. Indeed, mammals quickly took over once the terrible lizards were gone, the mammalian age began about 10 million years after the extinction of the Cretaceous-Paleogene.
After living in the shadow of dinosaurs for hundreds of thousands of years, our time had finally come.