A research paper co-authored by Brooklyn College and CUNY-based researchers has revealed that picrodontids—an extinct family of placental mammals that lived several million years after the extinction of the dinosaurs—are not primates, as previously believed.

The paper was published on January 10 in Royal Society’s Biology Letters and is significant in that it settled a paleontological debate that has been brewing for more than 100 years while helping to paint a clearer picture of primate evolution.

Stephen Chester

Stephen Chester

The research was done by Stephen Chester, the senior author and an associate professor of anthropology at Brooklyn College and the CUNY Graduate Center; Jordan Crowell, the lead author and adjunct lecturer in the Department of Anthropology at Brooklyn College and a Ph.D. candidate at the CUNY Graduate Center; and John Wible, curator of mammals at the Carnegie Museum of Natural History.

For the last 50 years, paleontologists have believed picrodontids, which were no larger than a mouse and likely ate foods such as fruit, nectar, and pollen, were primates, based on features of their teeth that they share with living primates. But by using modern CT scan technology to analyze the only known preserved picrodontid skull in the world at Brooklyn College’s Mammalian Evolutionary Morphology Laboratory. Crowell worked with Chester and Wible to determine they are not closely related to primates at all.

Chester, who serves as Crowell’s Ph.D. adviser, has both a professional and personal interest in this research. It was Chester’s renowned colleague and “academic grandfather,” Professor Emeritus Frederick Szalay from Hunter College (CUNY) and the CUNY Graduate Center, who, in 1968, first convincingly classified picrodontids as primates based on evidence from fossilized teeth. Szalay studied the teeth of the only known picrodontid skull, Zanycteris paleocenus, for his research—the same skull this team examined with the new technology that led to their discovery.

Jordan Crowell

Jordan Crowell works in Brooklyn College’s Mammalian Evolutionary Morphology Laboratory.

“The Zanycteris cranium was prepared and partially submerged in plaster around 1917, so researchers studying this important specimen at the American Museum of Natural History were not aware of how much cranial anatomy was hidden over the last 100 years” Chester said. “Micro-CT scanning has revolutionized the field of paleontology and allows researchers to discover so much more about previously studied fossils housed in natural history museum collections.”

“While picrodontids share features of their teeth with living primates, the bones of the skull, specifically the bone that surrounds the ear, are unlike that of any living primate or close fossil relatives of primates,” Crowell said. “This suggests picrodontids and primates independently evolved similarities of their teeth likely for similar diets. This study also highlights the importance of revisiting old specimens with updated techniques to examine them.”

CT scan technology revealed previously unknown bones of the skull (colored on the right) that helped demonstrate that picrodontids are not primates as previously believed.

The research was funded by grants Chester and Crowell secured through Brooklyn College from the National Science Foundation and The Leakey Foundation. Chester and Crowell are also currently working on several additional externally funded research projects focused on how primates and other mammals evolved following the extinction of the dinosaurs. They encourage undergraduates to contact them regarding funded research opportunities in the Mammalian Evolutionary Morphology Laboratory.