What it is
A small reptile that lived about 289 million years ago, in what is now Oklahoma. Its world was full of bigger hunters. Its bones washed into old caves there.
Why it matters
It could leave its tail behind. Across the middle of each tail bone runs a line. It is not a break. The bone grew that way, with a weak spot built in. Grab the tail, and it snaps along that line. Living lizards use the same trick. But this is not a lizard. Lizards came much later, and scientists think they found the trick again on their own. The young could do it best: in bigger, older animals, bone filled the line in. There is no sign it ever grew a tail back.
A mummy in the caves
Storms washed small animals into those caves, fine clay buried them, and oil seeping up from deep below soaked into them. In 2026, the caves gave up a Captorhinus mummy, still in its skin, banded like an accordion. Scientists looked inside the rock with neutrons and found its rib cage, cartilage and all. It is the oldest cartilage known from any land animal, and the rib cage was built to breathe by moving the ribs. Scientists think reptiles, birds and mammals inherited this way of breathing.
Read the sources
- Caudal autotomy as anti-predatory behaviour in Palaeozoic reptiles · Scientific Reports (2018)
- Mummified early Permian reptile reveals ancient amniote breathing apparatus · Nature (2026)
- Paleozoic cave system preserves oldest-known evidence of amniote skin · Current Biology (2024)
- Mummified remains reveal breathing and movement of ancient reptiles · ANSTO (2026)