Newly Discovered Fossil Tracks May Rewrite Early History of Reptiles
Fossilized claw tracks discovered in Australia show that the animal group that includes reptiles, mammals and birds formed earlier than expected
Illustration of an amniote animal thought to have left fossilized claw prints in Victoria, Australia.
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Fossil claw prints found in Australia were probably made by the earliest known members of the group that includes reptiles, birds and mammals, according to a study published in Nature today. The findings suggest that this group — the amniotes — originated at least 35 million years earlier than previously thought.
Early amniotes evolved to lay eggs on land, because they were encased in an amniotic membrane that stopped them drying out. Before this study, the earliest known amniote fossils had been found in Nova Scotia, Canada, and were dated to the mid-Carboniferous period, about 319 million years ago. The latest findings suggest that amniotes also existed in the early Carboniferous period, around 355 million years ago.
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The claw tracks were found in a sandstone block on the bank of the Broken River at Barjarg in the state of Victoria, by two co-authors of the paper who are not professional scientists. This area of the river is known as Berrepit to the Indigenous Taungurung people who own the land.
The sandstone block is part of a larger structure that had already been dated to the early Carboniferous on the basis of radiometric and tectonic evidence. Fossilized tracks of aquatic invertebrates and fish found in the same layer were also dated to this time period.
The Snowy Plains Formation trackway slab with footprints and trackways highlighted. Manus (front foot) prints are shown in yellow; pes (hind foot) prints are shown in blue.
There are no marks of dragging bellies or tails, and the authors suggest that the amniotes that left the tracks were able to keep their bodies and tails off the ground while they walked on land. But Salisbury questions that interpretation, because it would mean the animals had developed sophisticated structures for complex locomotion, which would be surprising given how early they are. “It seems more likely that the tracks were made by an animal that was ‘punting’ in shallow water, rather than walking on land,” he says.
Until now, evidence suggested that the last common ancestor of modern amphibians and amniotes lived around 352 million years ago. But if the ancestors of reptiles existed during the early Carboniferous, their split from amphibians must have occurred even earlier, says Long. Dating by the team suggests that the groups diverged in the Devonian period, about 380 million years ago.
This article is reproduced with permission and was first published on May 14, 2025.
Rita Aksenfeld writes for Nature Magazine.
First published in 1869, Nature is the world’s leading multidisciplinary science journal. Nature publishes the finest peer-reviewed research that drives ground-breaking discovery, and is read by thought-leaders and decision-makers around the world.
Source: www.scientificamerican.com