By Sid Perkins
Fossilized footprints found in an abandoned quarry in Poland hint that four-limbed creatures called tetrapods evolved much earlier and in a radically different environment than previously thought.
The footprints — many individual impressions, as well as some arranged in sets called trackways — are preserved in 395-million-year-old rocks in the Holy Cross Mountains, in the southeastern part of the country, paleontologist Per E. Ahlberg and colleagues report in the Jan. 7 Nature. That age substantially predates the time frame that paleontologists have pinned as the sea-to-land transition.
Evidence suggests that the carbonate rocks were laid down as sediments in the intertidal areas of a tropical shoreline, possibly in a lagoon, says Ahlberg, of Uppsala University in Sweden.