Scaly fossil is the oldest known piece of skin
Dry, flaky skin may be one of the least enjoyable parts of winter. But in general, tough, waterproof skin is part of what allowed the ancestors of modern reptiles, birds and mammals to move inland, while their thin-skinned amphibians stayed close to water.
In a published study Thursday in the journal Current Biologyscientists announce the discovery of the oldest known piece of fossilized skin. The pebble, which is no larger than a human fingernail, most likely belonged to an ancient reptile and offers rare insight into the evolution of the skin.
The piece of skin is one of countless traces of prehistoric life preserved in the Richards Spur limestone cave system near an oil seep in southwestern Oklahoma. When animals fell into the caves 289 million years ago, conditions were ideal for preservation: fine clay sediments quickly buried the bodies, low oxygen levels in the groundwater slowed the decay process, and hydrocarbons from the oil penetrated the tissues and made them less vulnerable. hospitable to bacteria. The tar seeped into the fossils and colored them.
In 2018, Bill May, a retired forensic analyst, shared some small flakes from the Richards Spur that he could not identify with Robert Reisz, a paleontologist at the University of Toronto, Mississauga.
“We got very excited by what we saw under the microscope,” says Dr. Reisz, author of the article.
“The texture of the skin is quite unique and interesting. It really stands out from other fossil material. It’s clearly not a bone,” said Ethan Mooney, a master’s student working with Dr. Reisz worked on the paper. In any case, the fossilized tissue bore a striking resemblance to the scaly skin of a crocodile.
A doctoral student and another author of the paper, Tea Maho, used a diamond-tipped blade to separate a small section of skin into hair-thin layers. The outer layers had hardened structures made of keratin, the protein found in the hair and nails of mammals. These hardened structures, or cornifications, are a characteristic of the skin of amniotes – the land-dwelling animals with a backbone, including reptiles, birds and mammals. The ancestors of Amniotes evolved to be able to live and reproduce outside of water, unlike their amphibious relatives.
Tough, impermeable skin was an important evolutionary adaptation for amniotes that took over the land, “because to survive in terrestrial environments, you don’t dehydrate,” Mr. Mooney said.
The fossilized skin was found on its own, separate from the bone. However, Richards Spur has yielded numerous fossils of a small, lizard-like reptile called Captorhinus aguti. Although scientists have not found a C. aguti fossil with skin attached, they have identified one with keratinization remains. Dr. Reisz said this suggests the skin came from the same animal.
Hans Sues, a paleontologist at the National Museum of Natural History who was not involved in the research, said he was “delighted” by the paper and agreed that it is “really the earliest fossil example” of skin.
“We took skin impressions, but here they can look at the detailed structure under the microscope as if it were skin they just took from a living animal,” said Dr. Sues. “And that is a very important discovery.”