Study suggests first primates lived in trees

NEW HAVEN » Our primate ancestors started out by living in the treetops, according to analysis of a partial skeleton by a team including Yale University researchers.

The 62 million-year-old Torrejonia — the oldest known primate skeleton — were discovered in the San Juan Basin, located mostly in northwestern New Mexico, by Thomas Williamson, curator of paleontology at the New Mexico Museum of Natural History and Science, and his twin sons, Taylor and Ryan, according to a Yale press release.

Torrejonia was a small mammal from an extinct group of primates called plesiadapiforms, which had flexible joints suitable for climbing and clinging to branches, the release says.

“This is the oldest partial skeleton of a plesiadapiform, and it shows that they undoubtedly lived in trees,” said lead author Stephen Chester, an assistant professor at Brooklyn College, City University of New York, and curatorial affiliate of vertebrate paleontology at the Yale Peabody Museum of Natural History, according to the release. “We now have anatomical evidence from the shoulder, elbow, hip, knee and ankle joints that allows us to assess where these animals lived in a way that was impossible when we only had their teeth and jaws.”

Torrejonia previously was thought to be a ground dweller based on cranial and dental fossils that were similar to animals that search for insects on the ground, the release said.

The study supports the theory that plesiadapiforms were the first primates. They appear in the fossil record shortly after non-avian dinosaurs went extinct, the release said. The remains comprise 20 bones, including parts of the cranium, jaws, teeth and portions of the upper and lower limbs, the release said. The presence of teeth helped identify the skeleton as Torrejonia; teeth are often used to identify extinct mammals, said Eric Sargis, professor of anthropology at Yale University and senior author of the study. Williamson is a co-author.

“To find a skeleton like this, even though it appears a little scrappy, is an exciting discovery that brings a lot of new data to bear on the study of the origin and early evolution of primates,” said Sargis, a curator of vertebrate paleontology and vertebrate zoology at the Peabody, where the partial skeleton was molded and casted for further study.

Sargis said plesiadapiforms had outward-facing eyes and relied on smell more than living primates do today, giving credence to the belief that they are transitional creatures between earlier mammals and modern primates, according to the release.

The skeleton was discovered in the Torrejon Fossil Fauna Area, a remote area in northwestern New Mexico administered by the federal Bureau of Land Management in order to protect the scientific value of fossils found there. A permit from the bureau enabled the collection of Torrejonia.

The study will be published Wednesday in the online edition of the Royal Society Open Science.

“This is the oldest partial skeleton of a plesiadapiform, and it shows that they undoubtedly lived in trees.” — Stephen Chester

PHOTO COURTESY YALE UNIVERSITY The bones recovered from Torrejonia, considered the first primate.