245-Million-Year-Old Fossil Reveals the Stomach of an Ancient Marine Reptile

A remarkably preserved fossil from China is giving scientists an extraordinary look inside a marine reptile that lived about 245 million years ago.

The animal, named Austronaga minuta, was only about 60 centimeters long. Yet its fossil preserves not only most of its skeleton, but also large parts of its digestive system, including the stomach, liver and intestines.

A Rare Look Inside an Ancient Animal

The fossil was discovered in what is now Yunnan Province in southern China. Researchers used techniques including ultraviolet photography and mass spectrometry to examine unusual material preserved inside the animal’s body.

The analysis revealed a large, sac-like stomach, a liver and a long section of intestine. Traces of hemoglobin were also detected in the preserved liver.

Its Last Meal Was Still There

Scientists also found fish scales inside the digestive tract. This provides direct evidence that Austronaga minuta fed on fish.

The discovery gives researchers an unusually detailed picture of how the small marine reptile lived and what it ate during the Triassic Period.

A Land Relative That Became a Swimmer

Austronaga belonged to the archosaur lineage, the broader reptile group that includes dinosaurs, birds and crocodiles. Its ancestors lived on land, but this animal had already developed specialized features for life in the sea.

Its long tail likely provided much of its propulsion, while its elongated front limbs helped with steering and stabilization. Its hind limbs were considerably smaller.

The Oldest Largely Complete Reptile Digestive System

Researchers say the fossil preserves the oldest known largely complete digestive system in a reptile. The organs appear relatively simple compared with those of modern birds and crocodiles.

The finding provides new information about how early archosaur relatives adapted to marine environments and how their bodies changed as they moved from life on land to life in the water.

Sources

• Science Advances — “Highly aquatic marine stem Archosaur with soft tissue preservation,” July 29, 2026.
• State Museum of Natural History Stuttgart — Research announcement on Austronaga minuta, July 30, 2026.
• Reuters — “Chinese fossil shows internal organs of prehistoric marine reptile,” July 30, 2026.
• ScienceDaily — “This 245-million-year-old fossil still has its stomach and intestines,” September 29, 2026.