Fossilized tracks from an early reptile are now the oldest known reptilian tracks, meaning the tetrapod ancestor most likely appeared earlier, during the Devonian period.
Their appearance pushes back amniotes evolution by 35-40 million years.
Amniotes are thought to have diverged from amphibians at the dawn of the Carboniferous period, about 355 million years ago.
They now think that the tetrapod ancestor appeared during the Devonian, and that amniotes began to diverge from them about 395 million years ago, 35 to 40 million years earlier than previously thought.
“The [fossil footprints] have a disproportionate impact on our understanding of early tetrapod evolution because of their combination of diagnostic amniote characteristics and early, securely constrained date,” the researchers said.
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The following is what this story will teach you.
It was once believed that the common ancestor of all tetrapods, including humans, appeared at the beginning of the Carboniferous period.
Since the earliest known reptilian tracks are fossilized tracks from an early reptile, the tetrapod ancestor most likely appeared earlier, during the Devonian period.
The clawed feet that amniotes have created these tracks. Their look delays the evolution of amniotes by 35–40 million years.
There was rain between 359 and 350 million years ago. Lizard-like creatures crawled through the mud in what was once Gondwana (but is now Australia), leaving behind footprints that became frozen in time, fossilizing as mud turned to stone over the aeons. The extent to which our tetrapod ancestors walked on land was later determined by the discovery of these footprints during an excavation.
Tetrapods, which translate to “four legs” from Greek, comprise all amphibians, reptiles, birds, and mammals. They are believed to have descended from lobe-finned fish that emerged from primordial seas using fins that served as primitive legs. Like all tetrapods (apart from amphibians), humans are amniotes, meaning that our eggs shield developing embryos in amniotic sacs. About 355 million years ago, at the beginning of the Carboniferous period, amniotes are believed to have split off from amphibians. Birds and reptiles would diverge from mammals just 30 million years later.
The fossil footprints were found near the edge of Broken River, a paleontological site in eastern Victoria (called Berrepit in Taungurung, the language of the indigenous people who live there). Whatever animal left footprints on the riverbank is the first indication of terrestrial life in this region. The footprints’ claw marks indicate the animal was an amniote, despite the fact that amniotes shouldn’t have evolved at such an early stage of the Carboniferous period.
In a study recently published in the journal Nature, the Swedish and Australian team of researchers who conducted excavations at the Berrepit site stated, “This pushes back the likely origin of crown-group amniotes by at least 35-40 million years.”. The Devonian/Carboniferous boundary cannot be significantly younger than [Amniotes], and the Devonian must be deep within [the origin of tetrapods].”. “”.
Prior to this discovery, Notalacerta tracks and Hylonomus bones were the oldest amniote fossils known to exist. Being sauropsids, these species belonged to a broader class of extant and extinct birds and reptiles that most likely existed in the late Carboniferous. The discovery of the enigmatic tetrapod footprints from Berrepit by this team of experts altered the belief that the common ancestor of all tetrapods first appeared in the early Carboniferous. The tetrapod ancestor is now believed to have emerged during the Devonian, and amniotes diverged from them approximately 395 million years ago, which is 35–40 million years earlier than previously believed.
Given that practically all amniotes have claws or nails, it is clear that the footsteps originated from an amniote rather than just a tetrapod. No signs of a body or tail being dragged across the ground are visible, and claw marks scuffed the damp ground following a brief downpour. Although its exact appearance is unknown, the distance between the fore and hind feet suggests that the animal was roughly 17 cm (6.7 inches) from shoulder to hip, with unknown neck, head, and tail lengths. The researchers calculated that it must have been around 80 cm (about 31½ inches) in length overall using a contemporary water monitor as a stand-in.
Tetrapods don’t show up in the fossil record for another 20 million years, which may be explained by the footprints. The end-Devonian mass extinction was believed to have had such a devastating effect. Compared to their pre-gap predecessors, tetrapods from after the gap are far more varied and developed. Since tetrapods must have been diverging from their common ancestor at some point during the Devonian, the mass extinction had minimal impact on tetrapod evolution, according to early Carboniferous sauropsid tracks.
Because of their combination of early, securely constrained date and diagnostic amniote characteristics, the researchers concluded that the [fossil footprints] have a disproportionate impact on our understanding of early tetrapod evolution. “They demonstrate, once more, the extraordinary importance of happenstance and serendipity in the study of severely under-sampled parts of the fossil record. “”.
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