Fossils changed history: They were alive 30 million years ago

Tracks discovered in the Australian state of Victoria date back to the Carboniferous period, about 350 million years ago, pushing back the evolutionary date of reptile-like animals by 30 to 40 million years, according to a new study published in the journal Nature.

"This is the oldest evidence in the world of reptile-like animals walking on land. Previously, fossils from the Northern Hemisphere alone were thought to be 35 to 40 million years younger," said study co-author and palaeontologist Prof John Long from Flinders University.

Modern reptiles, along with birds and mammals, belong to a group of animals called amniotes. These four-limbed vertebrates reproduce from eggs that contain a protective membrane surrounding the embryo, freeing them from dependence on water for their reproductive processes. This represents the largest evolutionary separation from amphibians.

Amniotes were thought to have evolved from amphibian-like ancestors around 320 million years ago, but the clawed footprints are 350 million years old, seriously questioning that estimate.

"A single piece of rock, only large enough for one person to carry, has led us to question everything we know about the evolutionary history of modern four-limbed vertebrates," said Prof. Per Ahlberg, a paleontologist at Uppsala University.

The tracks appear to have been left by a small creature with long fingers and clawed feet. Claws are a feature found only in early amniotes, so it is thought to have been a primitive reptile. These are the oldest clawed footprints yet discovered.

The researchers believe this finding suggests that reptiles may have actually evolved towards the end of the Devonian period, around the time when fish-like creatures like Tiktaalik first came onto land.