The Earliest Footprints

Researchers have uncovered the earliest evidence of four-legged animals. Footprints and tracks preserved in the mud of an abandoned quarry in southeastern Poland date back 395 million years, upending accepted thinking about when and where land animals first emerged.

Scientists have long believed that four-limbed animals--also known as tetrapods--evolved from fish via transitional animals called elpistostegids. These creatures had paired fins, rather than true arms and legs, and were capable of very limited crawling. The oldest elpistostegid fossils, known as Tiktaalik and Panderichthys, are 386 million years old.

But the Polish tracks suggest that elpistostegids were an evolutionary dead-end. The imprints found in the quarry are clearly footprints: in some of the prints, individual digits can be made out.…

Also see the story in the Guardian with a comment by Adam Rutherford, an editor at the science journal Nature.