Scaly Fossil Is the Oldest-Known Piece of Skin

Dry, scaly skin may be one of the least fun parts of winter. But in the broad scheme of things, a tough, watertight hide is part of what enabled the ancestors of modern reptiles, birds and mammals to move inland while their thin-skinned amphibian cousins remained close to water.

In a study published Thursday in the journal Current Biology, scientists announced the discovery of the oldest-known piece of fossilized skin. The pebbly scrap, which is no larger than a human fingernail, most likely belonged to an ancient reptile and provides rare insight into 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 an oil seep in southwestern Oklahoma. When animals fell into the caves 289 million years ago, the conditions were ideal for preservation: fine clay sediments rapidly buried the bodies, low levels of oxygen in the groundwater slowed the decay 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 tiny flakes from the Richards Spur that he couldn’t identify with Robert Reisz, a paleontologist at the University of Toronto Mississauga.

“We got very excited by what we saw under the microscope,” said Dr. Reisz, an author of the paper.

Different views of the skin samples, including cross-sections through flat, epidermal scales of the skin cast (B and C).Credit…Mooney et al., Current Biology 2024

“The texture of the skin is quite unique and interesting. It really stands out from other fossil material. It’s obviously not bone,” said Ethan Mooney, a master’s student who worked with Dr. Reisz on the paper. If anything, the fossilized tissue bore a striking resemblance to the scaly skin of a crocodile.

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