The scaly fossil is the oldest known piece of skin

Dry, flaky skin can be one of the least pleasant parts of winter. But in the grand scheme of things, tough, waterproof skin is part of what enabled the ancestors of modern reptiles, birds and mammals to move inland while their thin-skinned amphibian cousins ​​stayed closer to the water.

In a study published Thursday in Current BiologyScientists have announced the discovery of the oldest known piece of fossilized skin. The cobblestone scrap, no larger than a human fingernail, likely dates back to ancient reptiles and provides a rare look at the evolution of skin.

The piece of skin is one of countless traces of prehistoric life preserved in the Richards Spur limestone cave system near the oil spill in southwestern Oklahoma. When animals fell into caves 289 million years ago, conditions were ideal for preservation: fine clay sediments quickly buried the bodies, low oxygen levels in groundwater slowed the decomposition process, and hydrocarbons from the oil permeated the tissues and made them less hospitable to bacteria. The tar seeped into the fossils, staining them.

In 2018, Bill May, a retired forensic analyst, shared some microchips from Richard's Spear that he could not identify with Robert Rees, a paleontologist at the University of Toronto Mississauga.

“We were very excited by what we saw under the microscope,” said Dr. Rees, the study's author.

“The texture of the skin is very unique and interesting. It really stands out from other fossil material. It's clearly not bone,” said Ethan Mooney, a master's student who worked with Dr. Rees on the research. If anything, it's that the fossilized tissue was It bears a striking resemblance to the scaly skin of a crocodile.

A Ph.D. The student and another author of the paper, Te Maho, used a diamond-tipped blade to separate a small section of skin into thin layers of hair. The outer layers contained hard structures made of keratin, the protein found in the hair and nails of mammals. These hardened structures, or keratins, are the hallmark of the skin of amniotes, which are land-dwelling animals, including reptiles, birds and mammals. Amniote ancestors evolved to be able to live and reproduce outside of water, unlike their amphibian relatives.

Tough, impermeable skin was a key evolutionary adaptation for amniotes that dominated land, “because in order to survive in terrestrial environments, you don't have to dry out,” Mr Mooney said.

The fossilized skin is found alone, not attached to bone. However, Richards Spur has produced countless fossils of a small lizard-like reptile called Captorhinus agouti. While scientists have not found a C. agouti fossil with associated skin, they have identified one with remains of keratinization. Dr. Rees said this suggested the skin came from the same animal.

Hans Soes, a paleontologist at the National Museum of Natural History who was not involved in the study, said he was “delighted” with the research, agreeing that it was the “earliest fossil example” of a skin.

“We get skin impressions, but here they can actually look at the detailed structure under a microscope as if it were skin they just harvested from a live animal,” Dr. Seuss said. “This is a really important discovery.”