Spectacular fossil preserves internal organs of ancient marine reptile
A stunningly intact marine reptile named Austronaga minuta that lived around 245 million years ago may have looked like a miniature version of more famous later ocean predators, like plesiosaurs
A tiny, long-necked marine predator that lived 245 million years ago is the oldest reptile ever found with an intact digestive system.
The exquisitely preserved fossil, including almost the entire skeleton as well as the stomach, liver and intestines, was found in Yunnan province in China in 2023 and is named Austronaga minuta.
Even blood vessels and the scales of a partially digested fish meal are visible in the remains.
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“A fossil this age with such clear preservation of its organs is really a world treasure,” says John Long at Flinders University in Adelaide, Australia, who wasn’t involved in the research.
Austronaga dates back to the Triassic Period, when dinosaurs first evolved, but it isn’t a dinosaur. It belongs to a broader group called archosaurs, which includes dinosaurs, birds and crocodiles, but not other famous marine reptiles like mosasaurs or ichthyosaurs.
The archosaurs were incredibly diverse in the Triassic and included “all kinds of interesting and strange-looking reptiles”, says Stephan Spiekman at the Natural History Museum Stuttgart, Germany, a member of the team that analysed the fossil. Only later, during the Jurassic and beyond, did they become more restricted, mostly being limited to dinosaurs, including birds, and crocodiles.
This specimen is a mere 60 centimetres in length, but as it is the only known example and the reptile’s age at death is unknown, it is impossible to say whether the species grew larger, says Spiekman.
However, he is confident that it was unlikely to have reached the size of its very long relative Dinocephalosaurus, the “Chinese sea dragon”, which could easily grow to over 4 metres.
“This was certainly a good and agile swimmer, mainly using its tail for swimming, its long front flippers for steering and its long neck to catch fish,” says Spiekman. “Austronaga probably would have looked a little like a lizard or a croc trying to be a seal or an otter and likely would have had scaly skin, for example.”
The fossil shows that the basic plan of the reptilian digestive tract has changed little in 245 million years, he says, and the “straight and simple intestines is what we see in most modern predatory reptiles, including those eating fish”.
Although the fossil is of high quality, the internal organs of Austronaga are only preserved in two dimensions. This is unlike those of a 380-million-year-old fossil of an armoured fish that Long and his colleagues described in 2022, which is regarded as having the oldest known organs of any vertebrate.
“But this is still an incredibly well-preserved fossil,” he says.
Science Advances DOI: 10.1126/sciadv.aeb7528
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