The oldest known 3D fragment of fossilized skin – at least 21 million years older than any previous samples – has been discovered. The skin fossil, collected from a cave system in Oklahoma in the US, belonged to an early species of Paleozoic reptile and resembles both ancient and still-living animals.
Its pebbled surface is similar to crocodile skin, while hinged regions between its scales bears resemblance to the skin structures of snakes and worm lizards.
This particular fossil is the oldest example of a preserved epidermis – the outermost layer of skin – in terrestrial reptiles, birds, and mammals.
“The fact that it resembles the skin of reptiles still alive today shows how important these structures are for a species’ survival,” said first author Ethan Mooney, a paleontology graduate student at the University of Toronto.
Writing in the journal Current Biology, where the research has been published, he explained: “The epidermis was a critical feature for vertebrate survival on land.
“It is a crucial barrier between the internal body processes and the harsh external environment.”
Because the skin fossil was so tiny – smaller than a fingernail – co-author Tea Maho, also from the University of Toronto, used microscopic examination to reveal its epidermal tissues.
This is how the scientists determined that the fossil likely came from the skin of amniotes – the terrestrial vertebrate group that includes reptiles, birds, and mammals and which evolved from amphibian ancestors during the Carboniferous Period.
The team has not been able to determine exactly which species of animal or which region of the body the skin belonged to, but they believe that the structure of the skin may be what allowed the eventual evolution of bird feathers and mammalian hair follicles.
The skin fossil was collected from a cave system in Oklahoma.
“We were totally shocked by what we saw because it’s completely unlike anything we would have expected,” said Doctoral student Maho. “Finding such an old skin fossil is an exceptional opportunity to peer into the past and see what the skin of some of these earliest animals may have looked like.”
Mooney added: “Every now and then we get an exceptional opportunity to glimpse back into deep time.
“These types of discoveries can really enrich our understanding and perception of these pioneering animals.”
It is rare for skin and other soft tissues to be fossilized, but the researchers believe preservation was possible in this case because of where the fossil was found.
The skin fossil was discovered in Richards Spur in Oklahoma, a cave system that has fine clay sediments and is likely an oxygenless environment – features that would have slowed decomposition.
“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,” Mooney explained.
“But the kicker,” he continued, “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.”
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