Paleontologists working in southern Wyoming have identified a previously unknown species of omomyid primate, adding a new chapter to the story of one of the best-studied fossil lineages in North America.
Tetonius homunculus (colorized) by R. Bruce Horsfall from W.B. Scott’s History of Land Mammals in the Western Hemisphere.
The new species belongs to a family of small, big-eyed, tarsier-like primates called omomyids that lived in the forests of North America roughly 50 million years ago (Eocene epoch).
Named Tetonius varleyorum, the animal was comparable in size to a modern mouse lemur.
“Our paper is about a new species of an omomyid primate, a primate family close to the top of the family tree of modern primates — with lemurs on one side and apes, humans and monkeys on the other,” said Parker Rhinehart, a doctoral student with the Biodiversity Institute and Natural History Museum at University of Kansas.
“The branch point where they meet up at the top is where the omomyids fall.”
“They’re true primates, but they’re extinct. They appear about 55 or 56 million years ago across the northern hemisphere.”
Dozens of jaw and tooth fragments from Tetonius varleyorum was found at a single sandstone locality nicknamed Tim’s Confession, part of the Smiley Draw local fauna in the Great Divide Basin.
The site has already produced nearly 1,000 tooth-bearing jaw fragments representing a wide range of ancient mammals.
“Identifying ancient primate fossils in the field typically requires hunting tiny fossil jaws and teeth — the only body parts tough enough to withstand erosion over geologic time,” Rhinehart said.
“Our paper analyzes fossils from Smiley Draw, a different Wyoming locale outside of the better-sampled Bighorn Basin.”
“This is really important to the Tetonius story,” he added.
“Because so many scientific ideas only really consider the fossils from the Bighorn Basin, they just don’t take in the whole picture.”
“One of the things our paper points out is when you start incorporating fossils from outside of the Bighorn Basin, this picture becomes a little bit more complicated.”
What makes the new discovery of Tetonius varleyorum especially notable is not just the new species itself, but the company it kept.