Researchers have discovered a tiny 3D fragment of fossilised skin at least 21 million years older than any previously found. It has a pebbled surface that resembles that of modern day crocodiles, and is thought to have belonged to an early species of Paleozoic reptile.
The epidermis, the outermost layer of skin, was an important evolutionary adaptation in the transition to life on land. The researchers say that this skin may represent the ancestral skin structure that allowed for the eventual evolution of bird feathers and mammalian hair follicles.
“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,” says Ethan Mooney, a palaeontology graduate student at the University of Toronto, Canada.
The fossil was collected, along with several other specimens, from the Richard Spur limestone cave system in the US state of Oklahoma. Fossils from this site date back to about 289-286 million years ago during the Permian Period.
It was this cave environment that allowed the skin, which rarely becomes fossilised, to remain preserved.
“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,” says Mooney, who is first author of the paper describing the fossil in Current Biology.
“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 fossil is smaller than a fingernail, but Mooney says that it provides “an exceptional opportunity to peer into the past and see what the skin of some of these earliest animals may have looked like.”
“The epidermis was a critical feature for vertebrate survival on land. It’s a crucial barrier between the internal body processes and the harsh outer environment,” says Mooney.
This epidermis shares features with ancient reptiles and those still roaming the earth today, including hinged regions between epidermal scales that resembles structures in snakes and worm lizards.
