Paleontologist Stephen Chester and colleagues reveal new clues about early primate evolution

(Press-News.org) NEW YORK, March 3, 2026 — A new scientific study led by paleontologist Stephen Chester, an Anthropology professor at the CUNY Graduate Center and Brooklyn College, is shedding fresh light on how the earliest known primate relatives evolved and spread across North America after the extinction of the dinosaurs.

The research—published as the cover article in the Journal of Vertebrate Paleontology—was conducted in collaboration with scientists from the Denver Museum of Nature & Science. It focuses on Purgatorius, a small, tree-dwelling mammal that lived about 66 million years ago and is considered the earliest known relative of all primates, including humans. Chester served as lead author on the paper, alongside co-authors Jordan Crowell (a CUNY Graduate Center alumnus), Tyler Lyson, and David Krause of the Denver Museum of Nature & Science.

Until now, fossils of Purgatorius had only been found in northern regions such as Montana and Saskatchewan, leaving scientists with an incomplete picture of how and where these animals evolved.

Chester and his colleagues report the southernmost discovery of Purgatorius fossils ever found, uncovered in Colorado’s Denver Basin. The fossils were recovered through careful screen washing of ancient sediments at the Corral Bluffs study area.

“This discovery helps fill a gap in understanding the geography and evolution of our earliest primate relatives after dinosaur extinction,” Chester said.

The newly discovered fossils are tiny teeth that show a unique mix of features, suggesting they may belong to a previously unknown, early species of Purgatorius. Their presence in Colorado suggests that archaic primates originated in the north and then spread southward, diversifying soon after the mass extinction at the end of the Cretaceous Period.

The study also challenges long-standing assumptions about where archaic primates lived. Scientists thought Purgatorius might be absent from southern regions during this time, but the new findings suggest that this was likely due to limited fossil sampling, not true absence.

“Our results demonstrate that small fossils can easily be missed,” Chester explained. “With more intensive searching, especially using screen-washing techniques, we will undoubtedly discover many more important specimens.”

This work was supported in part by a nearly $3 million collaborative grant from the National Science Foundation that Chester and his colleagues received in 2023. Over the five years, this grant will continue to fund Brooklyn College undergraduate research assistants who sifted through excavated sediment in Chester’s laboratory, uncovering fossils of Purgatorius and other vertebrates that lived in the immediate aftermath of the dinosaurs’ extinction.

You can read more about this study in National Geographic.

 

About the Graduate Center of The City University of New York
The CUNY Graduate Center is a leader in public graduate education devoted to enhancing the public good through pioneering research, serious learning, and reasoned debate. The Graduate Center offers ambitious students nearly 50 doctoral and master’s programs of the highest caliber, taught by top faculty from throughout CUNY — the nation’s largest urban public university. Through its nearly 40 centers, institutes, initiatives, and the Advanced Science Research Center, the Graduate Center influences public policy and discourse and shapes innovation. The Graduate Center’s extensive public programs make it a home for culture and conversation. 

 

About Brooklyn College

Widely known for its offer of an excellent education at affordable tuition and recognized nationally for its diverse student body, Brooklyn College has been an anchor institution within the borough of Brooklyn and greater New York City for more than 90 years. With approximately 15,000 students in more than 100 undergraduate and graduate degree programs in the arts, humanities, sciences, education, and business, the college is renowned for its rigorous academics, award-winning faculty, distinguished alumni, and community impact. Part of the City University of New York (CUNY), Brooklyn College offers a vibrant and supportive student experience on a beautifully landscaped 35-acre campus in the borough’s Midwood neighborhood.

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