The fossilized fragment is smaller than a fingernail, but it is enough to reveal the details of a type of skin that people would easily recognize today: it looks like the rough hide of an alligator. It is the oldest vertebrate skin fossil, dating back 290 million years, recently revealed by an international team of scientists.
Details about the find have just been published in an article in the specialized journal Current Biology. Fossilized skin helps document a crucial phase in the history of life on the planet, with the consolidation of the presence of vertebrates – and, in particular, the ancestors of current reptiles, mammals and birds – on dry land.
Without frequent contact with water, they needed to develop an epidermis that did not allow them to lose moisture, and the formation of an outer layer of skin that was tougher and more protected was a crucial step towards this. It is not yet possible to know which animal the reinforced skin belonged to, but everything indicates that it was some type of reptile.
“Every once in a while, we get a glimpse into the deep past like this. It’s the kind of discovery that greatly enriches our understanding of these pioneering animals,” said Ethan Mooney, first author of the study and a graduate student in paleontology at the University of Toronto. , In Canada.
Mooney highlights that the discovery was probably only possible thanks to the exceptional geological conditions of the Richards Spur limestone caves, in the state of Oklahoma (United States), where the fossils originated.
“Animals used to fall into this cave system during the early Permian [período de origem dos fósseis] and they were buried in very fine clay sediments, which slowed the decomposition process,” explains the researcher. “But what made the biggest difference is that these caves were also a place where there were active oil spills at the time. Interactions with petroleum substances were probably what allowed the skin to be preserved.”
Other very favorable geological contexts also led to the preservation of so-called soft tissues – muscles, cartilage, skin and even feathers and hair – in other fossils around the world, including the famous feathered dinosaurs of China and the pterosaurs (flying reptiles) of the Araripe plateau, in Brazil. But the Oklahoma specimen is much older than all of them, being at least 20 million years older than the second oldest case of fossilized skin.
The preserved structure has the three-dimensional characteristics of a reptilian epidermis. In addition to the small “bumps” typical of current alligators and crocodiles, there is a kind of articulation between scales, as is the case with some current lizards and snakes.
Everything indicates that it was from structures like these that evolution worked to produce the other structures of the epidermis of fully terrestrial vertebrates (excluding amphibians), such as the hair of mammals and the feathers of birds, says the study.