Scientists have discovered the oldest known skin fossils, dating back long before the dinosaurs. The samples, found in a cave in Oklahoma, USA, show that reptile scales haven’t changed much in the last 286 million years.
The majority of fossils we see in museums are skeletons, and the reason is pretty simple: bones don’t decompose very quickly, so they have more time to fossilize. Soft tissues like skin, muscle and organs usually rot away or are eaten by scavengers soon after death, so we don’t find those often.
But under the right circumstances, it can happen. Bury it quickly enough in just the right medium and you can end up with a feathered dinosaur tail preserved in amber, a 133-million-year-old brain pickled in a bog, and a nodosaur still sporting skin and scales that looks like it’s just taking a nap.
Now, scientists at the University of Toronto have found the oldest fossilized skin known so far, at least 21 million years older than the previous record-holder for any animal. The sample dates back 286 to 289 million years, meaning it predates the earliest dinosaurs by at least 40 million years.
The skin belonged to some kind of early reptile, the team says, and intriguingly it looks like it could have been sloughed off a crocodile yesterday. It has a familiar pebbled surface, as well as hinged regions between scales that the scientists liken to snake skin.
Most of what we know about the skin of ancient animals comes from impressions – indirect imprints left on mud that harden into rock, before the skin decays away. In this case, the skin itself is preserved in a series of small, three-dimensional fragments, including the tough outer epidermis layer and the rarer, inner dermis layer.
The fossils were discovered in Richards Spur, a limestone cave system in Oklahoma, by fossil hunters Bill and Julie May. This location may have been the key to how the skin was preserved so well for so long.
“Animals would have fallen into this cave system during the early Permian and been buried in very fine clay sediments that delayed the decay process,” said Ethan Mooney, first author of the study. “But the kicker is that this cave system was also an active oil seepage site during the Permian, and interactions between hydrocarbons in petroleum and tar are likely what allowed this skin to be preserved.”
The specimens will be housed at the Royal Ontario Museum, where further study could reveal more insights into the skin of ancient animals.
The research was published in the journal Current Biology.
Sources: Cell Press via Science Daily, The Conversation