Tuesday, January 23, 2007

Most Primitive Primate Skeleton Discovered

New Paleocene skeletons and the relationship of plesiadapiforms to crown-clade primates.2007. J. I. Bloch et al. PNAS 104: 1159-1164.
The origins and earliest branches of primate evolution more ancient by 10 million years than previous studies estimated.

Composite (left) and reconstructed (right) skeletons of D. szalayi, the oldest known ancestor of primates. (Bloch, et al./ PNAS)

From the press release:

Researchers describe two new 56-million-year-old fossils, including the most primitive primate skeleton ever described. The new plesiadapiform species, Ignacius clarkforkensis and Dryomomys szalayi, were found just outside Yellowstone National Park in the Bighorn Basin.

An extensive evaluation of skeletal structures provides evidence that plesiadapiforms, a group of archaic mammals once thought to be more closely related to flying lemurs, are the most primitive primates.

At least five major features characterize modern primates: relatively large brains, enhanced vision and eyes that face forward, a specialized ability to leap, nails instead of claws on at least the first toes, and specialized grasping hands and feet. Plesiadapiforms have some but not all of these traits. The article argues that these early primates may have acquired the traits over 10 million years in incremental changes to exploit their environment.