The 289-million-year-old reptile, Captorhinus, in its death pose in a cave system. The fossil of the reptile, which was discovered in a cave system near Richards Spur, Okla., is unusual because some of its soft tissue was preserved in a state of mummification.Dr. Michael DeBraga
Scientists have discovered a breathtaking fossil – literally.
The mummified remains of a small, ancient reptile found in an Oklahoma cave have turned out to include not only bones but preserved cartilage and skin.
Significantly, the fossil shows the creature’s ribs and shoulders in a telltale arrangement that reveals how the animal was built for respiration – an innovation by early reptiles that was also passed on to our mammal ancestors, and to birds.
“Once you have the rib cage moving and operated by muscles, then you can have inhalation,” said Robert Reisz, a professor of vertebrate paleontology at the University of Toronto. “It really is a critical step.”
The fossilized shoulder and hand of the reptile.Ethan Mooney/Supplied
It was Dr. Reisz who first examined the fossil starting three years ago and who led a detailed study published online on Wednesday by the journal Nature.
The fossil, which belongs to the genus Captorhinus, was discovered several years earlier in a cave system near Richards Spur, Okla., where Dr. Reisz and his colleagues have long conducted research and previously uncovered a number of specimens. The age of the cave system has been dated at 289 million years.
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In terms of evolutionary and geologic history, that places the fossils found in the cave squarely within the Permian Era. This is well before the appearance of the first dinosaurs, but after the point when reptiles first appeared and evolved to be distinct from their amphibian ancestors.
In particular, amphibians require a watery environment as part of their life cycles. Reptile shoulders can move in a way that allows for a more mobile form of locomotion. They also have the ability to lay eggs on land, which freed them to move into new habitats.
To avoid destroying the rare tissue, researchers examined the specimen using a neutron beam that could detect the preserved organic material in the fossil.Ethan Mooney/Supplied
The development of breathing was another crucial feature of the reptilian tool kit that set the stage for further evolution, Dr. Reisz said.
Amphibians have wide skulls and mouths that help them to gulp air and take in oxygen. Once early reptiles had a muscular system that worked like a bellows to draw air in, then vertebrate heads could take on a variety of shapes.
“You can actually experiment with all kinds of shapes of skull, and that’s what gave rise to dinosaurs and living reptiles and mammals,” Dr. Reisz said.
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The newly described fossil is unusual because some of its soft tissue was preserved in a state of mummification. The chances of such preservation are extremely rare. It required the carcass of the creature to first dry out and then to fall into the oxygen-starved water in the cave where it became encased in minerals. Oil seeping through the rocks helped the preservation process.
To avoid destroying the rare tissue, researchers examined the specimen using a neutron beam that could detect the preserved organic material in the fossil. This allowed them to map out the traces of the skeletal system that provided information on the animal’s mode of respiration.
“The discovery of this fossil is exciting because the whole rib cage and the connection to the shoulder girdle are preserved,” said Elizabeth Brainerd, a professor of biology at Brown University in Rhode Island, who was not involved in the study.
“We know that the rib cage and shoulder girdle work together for breathing in modern lizards. This fossil shows that the same breathing mechanism was possible in this ancient reptile,” she said.