Research Report
Stephen Chester screening for Paleocene plesiadapiforms and other mammal fossils in Montana. Photo credit: Eric Sargis
As a PhD candidate at Yale University, Stephen Chester was awarded a Leakey Foundation research grant in the spring of 2010 for his project entitled “Origin and early evolutionary history of primates.”
Stephen Chester studies the fossils of plesiadapiforms. Plesiadapiforms are an extinct group of mammals from the Paleogene (66 to 23 million years ago) that are thought to be precursors to the primate order. Using phylogenetic and functional analyses, Chester is helping us better understand the origin and earliest history of primates. In other words, what makes primates different from the rest of Mammalia?
Results from this project include the naming of two new species of micromomyids, a basal plesiadapiform family, as well as the description of a new genus. In his team’s most recent paper published in PNAS, they describe the first known postcrania of the oldest plesiadapiform, Purgatorius. This also includes phylogenetic analyses that support all plesiadapiforms as primates.
A reconstruction of the micromomyid plesiadapiform Dryomomys szalayi by Doug Boyer 
Stephen Chester holding the ankle bones of Purgatorius. Photo credit: Stephen Chester
