_NATURE ENVIRONMENT Paleontology

_Fish n’ Hips

Newly described pelvic bone fossils from an ancient fish species challenge the existing theory of the evolution of walking in vertebrates.

_Ted Daeschler

Daeschler is an associate professor in the BEES department and associate curator and chair of vertebrate zoology at the Academy of Natural Sciences. His current research program in vertebrate paleontology focuses on the vertebrate fauna of the Late Devonian Period in eastern North America.

Scientists studying the fossil of an ancient fish species discovered 10 years ago have determined that the fish represents a key link in the evolution of hind legs, not just the front legs.

The team who discovered Tiktaalik roseae, a 375-million-year-old transitional species between fish and the first legged animals, suggest that the evolution of hind legs actually began as enhanced hind fins. This challenges the existing theory that large, mobile hind legs were developed only after vertebrates transitioned to land. Their findings were published in the Proceedings of the National Academy of Sciences.

The Tiktaalik fossil was discovered in 2004 in northern Canada by a team that included Drexel’s Ted Daeschler. Other team members were Neil Shubin of the University of Chicago, and the late Farish A. Jenkins Jr. of Harvard University.

A lobe-finned fish with a broad, flat head and sharp teeth, Tiktaalik looked like a cross between a fish and a crocodile.

Until recently, only material from the front portion of Tiktaalik had been described. The rear portion was retrieved when researchers investigated additional blocks recovered from the dig site.

The scientists speculate that it’s possible the fish could walk with its hind fins. African lungfish living today have similarly large pelves and walk underwater on the bottom.

Tiktaalik Pelvicbone

BALL_AND_SOCKET ‘HIP’

The pelvis bone has a prominent ball-and-socket hip joint, capable of operating like the joint of a limb.