New Delhi: The discovery of ancient fossil footprints of claws in Australia have scientists across the world re-examining evolutionary times of land-based vertebrates.
A study published in Nature Wednesday dates the fossil tracks to be approximately 355 million years old. It pushes the origin of the species back by 35 to 40 million years from what was earlier thought to be the point when tetrapods evolved from a group of fish that left the sea. This has an implication on the history of human evolution given that we are direct descendants of these tetrapods.
“I’m stunned,” Per Ahlberg from Uppsala University, who led the study, said in a media release. “A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved.”
It was two amateur explorers who discovered the tracks on the banks of the Broken River in Taungurung Country, Victoria, and alerted paleontologists. They were preserved on the upper surface of a loose but fine-grained silty sandstone block. In the Nature study, the authors called it a “demonstration of the value of citizen science.”
Uppsala University’s Ahlberg teamed up with paleontologists from Australia’s Flinders University.
“Once we identified this, we realised this is the oldest evidence in the world of reptile-like animals walking around on land, and it pushes their evolution back by 35-to-40 million years older than the previous records in the Northern Hemisphere,” said Professor John Long of Flinders University in a press release.
Their findings are threatening to upend our understanding of evolution of all tetrapods.
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When did the first tetrapods emerge?
As the word suggests, tetrapods include all species that have ‘four feet’. They are the first colonists on land and their origin began when fish transitioned from the oceans to adapt to life on land. They are the distant ancestors of all modern amphibians and amniotes that includes vertebrate animals like reptiles, birds and mammals, including humans.
The oldest known tetrapods had primitive fish-like forms, and could barely move on land. The separation of amphibians and amniotes was so far believed to have begun at the start of the Carboniferous period, some 355 million years ago. This separation is known as the tetrapod crown group node.
The new study changes what was previously known by suggesting that the separation dates back to the Devonian period, some 390 million years ago.
“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,” according to the media release from Uppsala University.
It’s the claws that have generated much excitement within the scientific community.
“Claws are present in all early amniotes, but almost never in other groups of tetrapods,” said Ahlberg. “The combination of the claw scratches and the shape of the feet suggests that the track maker was a primitive reptile.”
The study also suggests that tetrapods originated in Gondwana, the southern supercontinent which Australia was a part of. It also included present-day South America, Africa, Arabia, Madagascar, India, and Antarctica.
The researchers have also found new fossil reptile footprints from Poland, suggesting that tetrapods in the Euramerica—the supercontinent that formed during the Devonian period and included North America, Greenland, northern Europe, and Russia—also originated earlier than previously thought.
So far, researchers have found only fossilised footprints and no fossil bones of ancient tetrapods, but if the new timelines are correct, the fossil footprints findings suggest that the evolution into land-based animals occurred not just earlier but also much quicker than initially thought.
(Edited by Radifah Kabir)
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