A 245-Million-Year-Old Fossil Still Has Its Stomach, Liver and Intestines

Scientists have discovered an extraordinarily preserved marine reptile fossil in China that still contains traces of its stomach, liver and intestines after about 245 million years.

The animal, named Austronaga minuta, lived during the Triassic Period, not long after the greatest mass extinction in Earth’s history. Its remarkable preservation is giving researchers a rare look inside the body of an ancient reptile.

An Ancient Animal Frozen in Extraordinary Detail

The fossil is almost completely preserved and measures about 60 centimeters in length.

Austronaga had a long neck, an elongated tail and large front limbs shaped for life in the water. Its smaller rear limbs appear to have played only a limited role in swimming.

Although its ancestors lived on land, the animal had already developed highly specialized adaptations for moving through the sea.

Scientists Could See Inside Its Body

The most remarkable feature of the fossil was not its skeleton but the dark material preserved inside its rib cage.

Using techniques including ultraviolet photography and mass spectrometry, researchers identified several internal organs.

The preserved structures included a large, sac-like stomach, a liver and a long intestinal tract.

Researchers say this is the oldest known example of a largely complete digestive system preserved in a reptile.

A Surprisingly Simple Digestive System

The discovery also revealed something unexpected about the animal’s biology.

Modern birds and crocodiles have a two-part stomach, but Austronaga had only one stomach chamber.

Its intestines were also relatively short and simple, which is consistent with an animal that primarily ate meat or fish.

Fish scales preserved inside the digestive region provide further evidence that the small marine reptile was a fish-eater.

Its Liver Still Shows Traces of Ancient Blood Chemistry

Researchers were particularly surprised by the preservation of the liver.

The organ retained a reddish appearance, and chemical analysis detected elevated iron associated with traces of hemoglobin.

Finding such biological signatures in a fossil approximately 245 million years old provides researchers with an unusual opportunity to study soft tissues that normally disappear long before fossilization is complete.

A Reptile That Returned to the Sea

Austronaga belonged to the archosaur lineage, the larger reptile group that eventually gave rise to dinosaurs, birds and crocodiles.

Very few members of this lineage became highly adapted to marine environments. The new fossil shows that some early relatives of these animals were already capable of making significant evolutionary changes for life in the ocean.

Its long tail likely provided most of the propulsion, while its front limbs helped with steering and stabilization.

A Window Into Life After the Great Extinction

Austronaga lived roughly 245 million years ago, only a few million years after the end-Permian mass extinction that wiped out a huge proportion of Earth’s species.

The oceans were undergoing major ecological changes during this period, and new groups of marine reptiles were beginning to appear.

The fossil therefore provides scientists with information not only about one unusual animal, but also about how reptiles adapted to rapidly changing ecosystems after one of Earth’s greatest biological crises.

A Tiny Fossil With a Remarkable Story

Most fossils reveal only bones and teeth. In this case, scientists can study both the animal’s skeleton and parts of its internal anatomy.

That combination makes Austronaga minuta an unusually valuable fossil for understanding how early reptiles evolved from land-dwelling ancestors into specialized marine animals.

More than 240 million years after the animal disappeared, its preserved organs are giving scientists an extraordinary glimpse inside a body from a world long before dinosaurs became dominant.

Sources

• ScienceDaily — “This 245-million-year-old fossil still has its stomach and intestines” — September 29, 2026.
• Reuters — “Chinese fossil shows internal organs of prehistoric marine reptile” — July 30, 2026.
• Staatliches Museum für Naturkunde Stuttgart / EurekAlert! — “Spectacular discovery provides insight into the internal organs of a marine reptile” — July 29, 2026.
• Science Advances — “Highly aquatic marine stem archosaur with soft tissue preservation” — 2026.