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+--- Thread: Research Earliest reptile footprints rewrite the timeline of tetrapod evolution (/thread-17998.html)
Earliest reptile footprints rewrite the timeline of tetrapod evolution - C C - May 15, 2025
https://www.eurekalert.org/news-releases/1083321
INTRO: "I'm stunned." says Per Ahlberg of Uppsala University, who coordinated the study; "A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved."
The story of the origin of [ur=https://en.wikipedia.org/wiki/Tetrapod]tetrapods[/url] began with fishes leaving the water, and ended with the descendants of these first colonists on land diversifying into the ancestors of the modern amphibians and amniotes (the group that includes reptiles, birds and mammals). The timeline of these events has seemed clear-cut: the first tetrapods evolved during the Devonian period and the earliest members of the modern groups appeared during the following Carboniferous period.
The earliest amniote fossils are from the late Carboniferous, about 320 million years old. This led researchers to conclude that the beginning of the evolutionary radiation of the modern groups, the point on the evolutionary tree where the ancestors of amphibians and amniotes separated (also known as the 'tetrapod crown-group node'), lay in the earliest Carboniferous around 355 million years ago. The Devonian period was seen as inhabited by more primitive fish-like tetrapods and transitional 'fishapods' such as [rul=https://en.wikipedia.org/wiki/Tiktaalik]Tiktaalik[/url].
A sandstone slab from the earliest Carboniferous of Australia, approximately 355 million years old, discovered by two amateur palaeontologists who co-authored the study, changes all this. It carries well-preserved footprints of long-toed feet with distinct claw impressions at the tips. These are by far the earliest clawed footprints ever discovered.
“When I saw this specimen for the first time, I was very surprised, after just a few seconds I noticed that there were clearly preserved claw marks.” says Grzegorz Niedźwiedzki of Uppsala University, co-author of the study.
"Claws are present in all early amniotes, but almost never in other groups of tetrapods." adds Per Ahlberg; "The combination of the claw scratches and the shape of the feet suggests that the track maker was a primitive reptile."
If this interpretation is correct, it pushes the origin of reptiles, and thus amniotes as a whole, back by 35 million years to the earliest Carboniferous. Further support comes from new fossil reptile footprints from Poland, also presented in the study; not as old as those from Australia, but also substantially older than previous records.
This recalibration of the origin of reptiles impacts the whole timeline of tetrapod evolution. The tetrapod crown-group node must be older than the earliest amniotes, because it is a deeper branching point in the tree, but how old exactly? The authors address this problem by combining data from fossils and modern DNA... (MORE - details, no ads)