355-Million-Year-Old Footprints Just Rewrote Reptilian History

The origin of four-limbed animals known as tetrapods was thought to be fairly straightforward: Fish flopped onto land in the Devonian, evolved, and eventually diversified into the reptiles, birds, mammals, and other creatures that cover the Earth today. But now, a slab of sandstone small enough to be carried by a single person has thrown that tidy timeline into chaos. The slab is from southeastern Australia and dates to about 355 million years ago, shortly after the end of the Devonian. Discovered by two amateur paleontologists (co-authors of a new study describing the find), the rock preserves a set of remarkable footprints: long-toed impressions with unmistakable claw marks. These trace fossils now represent the oldest clawed tetrapod tracks ever found. “The key impact is that it pushes an important part of the tetrapod evolutionary tree—in essence, all the branches that go below the reptile-mammal split (also known as the amniote crown-group node)—back in time,” said Per Ahlberg, ... Read full article.