Oldest skin fossil, dating back 21 million years, found in Oklahoma

A fossilized skin dating back 21 million years has been identified, likely belonging to an early species of Paleozoic reptile. This exceptionally well preserved specimen is now recognized as the oldest known skin fossil ever discovered. Microscopic inspection revealed that the fossil has a pebbled surface resembling crocodile skin.

The fossil came from the Richards Spur limestone cave system in Oklahoma. This tiny skin fossil, smaller than a fingernail, constitutes the preserved —the outermost layer of skin in terrestrial reptiles, birds, and mammals. This finding is considered crucial evidence for understanding the evolutionary adaptations during the transition to life on land.

“We were totally shocked by what we saw because it’s completely unlike anything we would have expected. 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,” said Ethan Mooney, a paleontology graduate student at the University of Toronto.

Rare fossil find This finding is extremely unusual since skin and soft tissues are rarely preserved as fossils. The remarkable preservation of this fossilized skin over an extensive period can be attributed to the distinctive characteristics of the cave system. According to the release, the site showcases features such as fine clay sediments that impeded decomposition, oil seepage, and an oxygen depleted cave environment.

“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 Mooney. “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,” added Mooney in the .

Pinpointing the animal species is challenging for the team, given that the skin fossil lacks skeleton remains. This ancient skin's resemblance to present day reptiles underscores the critical role these structures play in ensuring survival in land ecosystems. “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,” Mooney concluded. The findings were reported in the journal . The richest and most diverse assemblage of early terrestrial tetrapods (289 286 Mya1) is preserved within the infilled cave system of Richards Spur, Oklahoma.

Some of the oldest known terrestrial amniotes2,3 are exqui sitely preserved here because of early impregnation and encasement of organic material by oil seep hydro carbons within rapidly deposited clay rich cave sediments under toxic anoxic conditions.4 This phenomenon has also afforded the preservation of exceedingly rare integumentary soft tissues, reported here, providing critical first evidence into the anatomical changes marking the transition from the aquatic and semiaquatic lifestyles of anamniotes to the fully terrestrial lifestyles of early amniotes.

This is the first record of a skin cast fossil (3D carbonization of the skin proper) from the Paleozoic Era and the earliest known occurrence of epidermal integumentary structures. We also report on several compression fossils (carbonized skin im pressions), all demonstrating similar external morphologies to extant crocodiles.

These fossils serve as invaluable references for paleo reconstructions. A variety of previously unknown ossifications, as well as what are likely palpebral ossifications of the deeper dermis layer of the skin, are also documented. Chromato graphic analysis of extractable hydrocarbons from bone and cave samples indicates that the source rock is the Devonian age Woodford Shale.

Hydrocarbons derived from ancient marine organisms interacting with geologically younger terrestrial vertebrates have therefore resulted in the oldest known preservation of amniote skin..