The finding of the traces of the claws of an amniot (an ancestor of the reptiles) of 356 million years fossilized in a rock shows that the origin and evolution of these vertebrates was earlier than expected.
The details of the study, led by the University of Uppsala, in Sweden, and made in collaboration with scientists from Poland and Australia, have been published in Nature magazine.
The origin of life on earth began at sea. It was not up to about 150 million years later when the first tetrapods (four -legged animals) left the marine medium and reached the mainland.
The tetrapods were the ancestors of the amniots and modern amniot (the group that includes reptiles, birds and current mammals), the true colonizers of the earth.
The chronology seems clear: the first tetrapods – peeled to fish – evolved in the devonic period and, then, the first members of the modern groups, the amniotas, in the following period, the carboniferous.
In the fossil registry, the first preserved amniotas are from the late carboniferous, about 320 million years ago, which led researchers to think that the point of the evolutionary tree in which the ancestors from the amphibians and amniotas separated happened in the early carboniferous, 355 million years ago.
However, a piece of early carboniferous sandstone, about 356 million years old, discovered by two amateur paleontologists in Australia, has altered all this chronology.
The authors believe that this finding advances in 35 million years the origin of the reptiles, and therefore of the amniotas as a whole, to the earliest carboniferous.
Footprints of the same animal
The slab, which measures about 50 cm and was recovered in the Snowy Plains Training of Victoria (Australia), contains two fingerprint sets, apparently from the same animal, some brands made 356 million years ago by the claws of an amniot, about 40 million years before the traces and fossils of amniotes known so far.
These well -preserved footprints show long legs with claws on the tips.
When analyzing the separation between the front and rear footprints, the authors believe that the old amniot could measure about 80 cm, although they emphasize that it is not possible to know the exact proportions of the animal.
For the authors, this finding implies that the common ancestor of modern amniotas could have existed in the boundary between the devonic and the carboniferous (about 359 million years ago), and that the moment of separation of the tetrapods (which unites the lineages of the amniots and modern amniot) took place at the beginning of the upper devonic (about 380 million years ago).
That is, it is likely that the evolution of tetropods from aquatic creatures to other completely land occurred faster than was thought.
“When I saw this specimen for the first time, I was very surprised, within a few seconds I saw that there were clearly preserved claw marks,” says Grzegorz Niedźwedzki, from the University of Uppsala, co -author of the study.
“The claws are present in all the primitive amniot, but almost never in other groups of tetrapods. The combination of claw scratches and the shape of the feet suggests that the author of the fingerprints was a primitive reptile,” says the research coordinator, per Ahlberg, of the University of Uppsala.
If this interpretation is correct, it advances in 35 million years the origin of the reptiles, and therefore of the amniotas as a whole, to the earlier carboniferous.
In addition, the study provides new footprints of reptile fossils from Poland, which are not as old as those of Australia, but much more than the previous records.
This recalibration of the origin of reptiles affects the entire chronology of the evolution of tetrapods.
The Australian slab with the footprints “represents the entire fossil record of tetropods of the earlier carboniferous of Gondwana, the gigantic supercontinent that includes Africa, South America, Antarctica, Australia and India. Who knows what else lived there?” Ahlberg asks.
“The most interesting discoveries are yet to come and it is still a lot to find on the ground. These traces of Australia are just an example of it,” says Niedźwiedzki.
With EFE information
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