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Researchers uncovered a small patch of preserved reptile skin in the Richards Spur cave in Oklahoma that dates to roughly 289 million years ago, older than any skin fossil found before.
Researchers at the University of Toronto Mississauga (UTM) studied the tiny piece to learn how skin changed when animals moved from oceans onto the land.
Cave-fill sediment from the Oklahoma site passed through screens, and one dark fleck survived the rough handling.
The work was led by Ethan D. Mooney, a paleontology master’s student at UTM, with training in fossil anatomy. His research tracks how skin and skeleton traits helped early reptiles live farther from water without drying out.
Fossilized skin is very rare
Soft skin usually vanishes within days, because microbes and scavengers break cells apart soon after death.
Research on vertebrate fossils finds original soft tissues in only limited environments, leaving huge stretches of time without any skin record.
That scarcity makes a single patch of ancient skin valuable, but it also means scientists must treat every detail carefully.
Monsoon-like rains sometimes swept carcasses and loose bones off the surface, sending them into cave cracks and mud.
A separate study traced bone wear to transport inside the caves and identified three main entry routes.
Those routes help explain why most fossils arrive as scattered pieces, which makes a skin patch even harder to keep intact.
Oil and low oxygen
Sticky hydrocarbons – oil-based molecules made mostly of hydrogen and carbon – seeped into cave mud and coated buried remains.
That coating blocks oxygen and water from reaching microbes, so decay slows before the tissue collapses.
Low-oxygen pockets in the sediment add another brake on decay, yet the same tar can blur fine chemical clues.
Under a microscope, the fossilized skin fragment looked like pebbled reptile skin, with wrinkles that resemble modern crocodiles.
The specimen measured about fingernail size, and it was as thin as a human hair.
Those proportions left little room for error during preparation, since a single scrape could erase the pattern forever.
Scales built for movement
Bands of folded scales appeared in rows, and thin hinge zones separated them where the surface could flex.
That layout lets a tough outer layer move with the body, because the hinges bend while the scales stay rigid.
Finding that pattern in such an old animal hints that many reptile scale designs locked in early and stayed stable.
Guessing the animal
The fossilized skin fragment lacked an attached skeleton, so researchers compared its texture with animals already known from the site.
They argued it most likely came from Captorhinus aguti, a small lizard-like reptile that shows up often in that cave system.
Because several different skin patches were collected separately, the team also allowed that more than one species could be involved.
Amniotes before dinosaurs
The find opens a window on amniotes – vertebrates whose embryos develop inside protective membranes – long before dinosaurs appeared.
Their success on dry ground depends on more than eggs, since bodies also need skin that slows water loss.
A preserved surface from this era helps fill a gap between bones and behavior, where survival details usually disappear.
A barrier against drying
Modern reptile skin limits water loss and blocks pathogens, because a hardened outer layer seals the surface.
Cells in that outer layer are packed with tough proteins, so the surface resists drying and minor scrapes.
When the fossilized skin fragment shows a familiar scale layout, it suggests that basic water-saving design emerged very early.
3D layers in the fossilized skin
Microscope work showed a three-dimensional cast, not just a flat stain, so researchers could inspect thickness and folds.
They cut tiny sections for histology, a method that examines thin tissues slices under a microscope, which separates the outer layer from deeper support.
Those slices also revealed hinge-like borders between scales, yet the chemistry of the original skin could not be fully read.
Chemistry from ancient tar
Chemical fingerprinting connected the tar in bones and cave samples to the Woodford Shale, a much older rock unit.
Matching patterns of oil molecules point to a shared source because different rocks create different mixes as they mature.
That old petroleum may have sealed the fossilized skin fragment early, but it also complicates tests that look for surviving proteins.
Limits and open questions
A single skin patch cannot reveal the whole animal, since body region and age can change scale size and shape.
Tar impregnation protects tissue by sealing spaces, but it can also obscure pores and glands that once sat in the surface.
That cave system represents a special setting, so scientists should not assume every early reptile carried identical skin in every climate.
Lessons from this fossilized skin
A skin surface from this time gives artists and scientists a firmer guide for rebuilding early reptile bodies and movements.
“These fossils also serve as invaluable references for paleontological reconstructions,” wrote Mooney.
If scale and hinge features were already in place, later changes such as feathers and hair likely built on that base.
The cave chemistry and the skin structure show that early land vertebrates already carried tough, flexible outer coverings.
Future finds will need better links to whole skeletons, so researchers can map where each scale type sat on the body.
The study is published in Current Biology.
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