An extraordinarily preserved specimen of Austronaga minuta, a small, long-necked marine reptile from the Triassic era of China, showcases a fossilized stomach, liver, and intestines. This discovery provides paleontologists with their oldest detailed insights into how early reptiles digested food.
Austronaga minuta thrived in the Tethys Ocean during the Middle Triassic period, approximately 244 million years ago.
This species belonged to the tanysaur group, a distant ancestor of the lineages that eventually evolved into dinosaurs, crocodiles, and birds.
“Despite measuring only 60 cm, Austronaga minuta possessed a remarkably elongated neck and tail,” said Dr. Wei Wang of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences. “It was highly adapted for aquatic life, using its long tail for propulsion and its fin-like front limbs for steering and stabilization.”
“Conversely, its hind legs were significantly reduced and contributed minimally to swimming,” Dr. Wang added.
“This unique morphology is fascinating, considering that Austronaga minuta is not closely related to other well-known marine reptiles, such as ichthyosaurs or giant mosasaurs, which exhibit similar swimming techniques.”
In their research, scientists re-evaluated a nearly intact skeleton of Austronaga minuta initially described two years prior.
Not only is the skeleton largely complete, but it also preserves details of soft tissues: a stomach, liver, and intestines. Ultraviolet photographs aided scientists in mapping the outlines of these organs, revealing a liver characterized by a reddish hue likely attributed to iron-rich remnants from decayed blood.
The digestive structure of this creature was surprisingly rudimentary, featuring a simple, single-chambered stomach and a short, loosely coiled intestine, resembling more a fish-eating monitor lizard than a fully marine specialist.
The authors propose that this simplicity reflects reduced evolutionary pressure on internal anatomy relative to the significant adaptations seen in the limbs and pelvis.
The holotype specimen of Austronaga minuta. Image credit: Wei Wang.
“In comparison to the highly specialized exterior of Austronaga minuta, its internal organs appear less modified,” Dr. Wang noted. “The preserved organs feature a prominent, sac-like stomach, followed by a notably red liver containing detectable traces of hemoglobin.”
“Behind this structure is a lengthy, uncomplicated tube representing the small and large intestines,” he added. “Overall, this reveals that the digestive system of Austronaga minuta was considerably simple in design.”
This fossil serves as the oldest known instance of a largely intact digestive system in a reptile.
“Modern birds and crocodiles possess a two-part stomach, whereas Austronaga minuta only had a single stomach chamber,” said Dr. Nick Fraser from the National Museums Scotland. “This suggests that archosaur stomachs were initially quite simplistic before evolving further.”
“Interestingly, Austronaga minuta exhibited a relatively brief and uncomplicated digestive tract, akin to today’s fish-eating reptiles.”
As Austronaga minuta’s close relatives span from predominantly terrestrial to highly aquatic forms like Dinocephalosaurus, paleontologists argue that this lineage offers a rare perspective on the transition from land to sea in reptiles.
“This discovery transforms our understanding of early archosauromorph ecology, highlighting that the marine colonization by stem archosaurs occurred earlier and more extensively than previously recognized,” the researchers concluded.
“The transition from land to sea for this major reptilian clade began early in the Mesozoic era, paralleling the more renowned, long-lasting marine reptile groups such as Sauropterygia and Ichthyosauria, along with other entirely Triassic clades like Thalattosauria.”
“Overall, these findings indicate a broader adaptive strategy among reptiles to thrive in arid regions like those in southern China during the Triassic.”
The full study is published in the journal Science Advances.
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Wei Wang et al. 2026. Highly aquatic marine stem archosaur with soft tissue preservation. Science Advances 12 (31); doi: 10.1126/sciadv.aeb7528
Source: www.sci.news
