Palacrodon: A New Piece in the Mass Extinction Puzzle

Image courtesy of Kelsey Jenkins.

Around 250 million years ago, about ninety percent of living species died out in the end-Permian mass extinction. A recent study led by researchers at Yale University provides new insight into the following recovery period.

The researchers took computerized tomography (CT) scans of an Antarctic specimen of Palacrodon, an early reptile. The fossil was dated to the early Triassic period, just after the mass extinction. “People have looked at this fossil before, but returning with new techniques like CT scanning and digital imaging allows us to get a lot of new information… we can look at the internal surfaces of the bones, and things that would have normally been hidden or obscured by rock,” said Dalton Meyer, a graduate student in Yale’s Department of Earth and Planetary Sciences and coauthor on the study.

The data helps fill a gap in the reptile evolutionary tree. Modern reptiles have long, thin stapes, a bone in the middle ear adapted to high-frequency sounds, whereas earlier reptiles had a thicker version. Palacrodon occupies a middle ground. “Early reptile ancestors had a big blocky one, and modern reptiles have a really thin one, and Palacrodon shows evidence of the transition,” said Kelsey Jenkins, first author of the study and a PhD candidate at Yale’s Department of Earth and Planetary Sciences.

The researchers noted Palacrodon’s plant-eating teeth and toe bones were possibly adapted for climbing. These arboreal adaptations indicate greater tree presence than has usually been estimated so soon after the end-Permian extinction. “Because it’s Antarctica and we don’t have a lot of data there, maybe something weird was going on, or maybe there’s a global response that we haven’t calculated yet. It leaves a lot of room for speculation,” Jenkins said.

What’s next for the researchers? More Palacrodon! “I just sent an email to get more Palacrodons,” Jenkins said.