By Science Daily (Science) | Created at 2026-09-30 14:37:59 | Updated at 2026-09-30 19:02:12
1 day ago
A remarkably preserved fossil from China is giving scientists an unusually detailed look inside a marine reptile that lived about 245 million years ago.
Researchers from China, Europe, and the USA, including Dr. Stephan Spiekman, a paleontologist at the State Museum of Natural History Stuttgart and the University of Hohenheim, have described an exceptional specimen of the long-necked marine reptile Austronaga minuta. Although its ancestors lived on land, Austronaga had already developed sophisticated adaptations for life in the water by the Middle Triassic.
The fossil is nearly complete and preserves not only most of the animal's skeleton, but also large portions of its digestive system. Using modern analytical techniques, researchers identified several internal organs, including the stomach, liver and intestines. It is the oldest known example of a largely complete digestive system preserved in a reptile.
The findings have been published in Science Advances.
A Small Reptile Built for Life at Sea
Long-necked marine reptiles were common in the seas covering parts of what is now China during the Triassic period, and scientists have discovered fossils of several different species. Even so, the newly studied Austronaga minuta specimen stands out.
The animal measured only about 60 centimeters in length, yet it had an unusually elongated neck and tail. Its anatomy shows that it was already highly specialized for swimming. The long tail likely provided propulsion, while the extended, fin-like front legs helped with steering and stabilization. Its hind legs were much smaller and appear to have contributed little to swimming.
That body plan is especially surprising because Austronaga was not closely related to famous marine reptiles such as ichthyosaurs or giant mosasaurs, despite using a similar swimming strategy. Instead, Austronaga was closely related to land-dwelling archosaurs, the broader reptile group that includes crocodiles and dinosaurs.
"The archosaurs and their ancestors were the most diverse group of reptiles on land during the time of the dinosaurs, but we always thought that their adaptation to life in the sea was limited. However, the discovery of Austronaga shows that early representatives of this lineage had already developed complex adaptations to life in the oceans, comparable to those of other, better-known groups of fossil marine reptiles," says Dr. Stephan Spiekman, a specialist in long-necked marine reptiles, who is also the co-author of the study.
The Oldest Known Largely Complete Reptile Digestive System
The fossil became even more unusual when researchers examined a dark area preserved between its ribs. Closer analysis showed that the material represented the remains of a largely intact digestive tract.
Scientists used several techniques, including UV light photography and mass spectrometry, to study the material and identify multiple internal organs.
"Compared with the highly specialized body shape of Austronaga, its internal organs seem less modified. The preserved organs include a large, sac-like stomach at the front, followed by a strikingly red liver in which traces of hemoglobin can still be detected. Behind this is a long, simple tube forming the small and large intestines. The overall arrangement shows that the digestive system of Austronaga was relatively simple in structure," says Dr. Wei Wang, lead author of the study and marine reptile expert at the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing. "This fossil is the oldest known example of a largely complete digestive system in a reptile."
Despite the reptile's highly specialized swimming anatomy, its digestive organs appear to have retained a relatively simple arrangement.
"While today's birds and crocodiles have a two-part stomach, Austronaga had only a single stomach chamber. This shows that the stomachs of archosaurs were initially quite simple and only evolved later in the evolutionary process," explains Dr. Nick Fraser of the National Museums Scotland, one of the study's authors. "It is also striking that Austronaga had a fairly short and uncomplicated digestive tract, very similar to that of today's fish-eating reptiles."
New Clues to Reptile Evolution
The discovery provides researchers with an unusually complete snapshot of both the external and internal anatomy of an early marine reptile. It also offers new evidence for how quickly some relatives of land-dwelling archosaurs developed complex adaptations for life in the ocean.
The research was carried out by scientists from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing (China), the National Museums Scotland (UK), the State Museum of Natural History Stuttgart (Germany), the University of Hohenheim (Germany), The Field Museum in Chicago (USA), the Luoping Biota National Geopark (China) and the University of Zurich (Switzerland).
The work forms part of a broader investigation into the early history of modern reptile groups and the diversity of reptiles that inhabited Triassic seas. Researchers hope future discoveries will provide additional clues about the evolutionary history of marine reptiles and their relatives that remained on land.
The fossil is located in Beijing.
