Lurking in the Middle Triassic seas over what is now China, a highly adept marine reptile ate a fish for its last meal before it perished and became fossilized. This marine reptile, known as Austronaga minuta, descended from land-dwelling ancestors and appears to have a much simpler digestive system than its descendants would later have.
Thanks to the discovery of a nearly complete 245 million-year-old Austronaga fossil, an international research team is getting a better look at one of the oldest digestive systems in a reptile to date by using advanced technology. Publishing their findings in Science Advances, the research team says that thanks to this fossil, they now have one of the most detailed views of a prehistoric creature's full skeleton and digestive system.
“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,” Nick Fraser of the National Museums Scotland, one of the study's authors, said in the press release. “It is also striking that Austronaga had a fairly short and uncomplicated digestive tract, very similar to that of today's fish-eating reptiles.”
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What Did Austronaga Look Like?* *
Like many other marine reptiles, Austronaga has a long neck, fins, and sharp teeth. While marine reptiles like this were not uncommon in the oceans at that time, Austronaga, according to the study, had a few unique features.
Austronaga was only about 2 feet long, and for that size, its neck and tail were strikingly long, according to a press release. That tail, however, helped propel Austronaga through the water while its front fins steered. Its back fins were much smaller, and likely didn’t help in swimming at all.
What surprised the research team about Austronaga’s body is that though it looks similar to other marine reptiles, it’s not related to any of them, including ichthyosaurs — which each have a similar swimming method. Instead, Austronaga is more closely related to archosaurs, a land-dwelling group that includes dinosaurs and crocodiles.
“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," Stephan Spiekman, a specialist in long-necked marine reptiles who is also the co-author of the study, said in a press release.
“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," Spiekman added.
A Unique Marine Reptile With A Unique Stomach
The research team used UV light photography and a mass spectrometer to analyze the fossilized remains. From these methods, they noticed a dark region between the fossil’s ribs. This turned out to be the remnants of a nearly intact digestive tract.
“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,” Wei Wang, lead author of the study and marine reptile expert at the Institute of Vertebrate Paleontology and Palaeoanthropology in Beijing, said in the press release. “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.”
This detailed look at the digestive tract revealed a lot about Austronaga, including that it had a different digestive tract compared to other archosaurs.
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Article Sources
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- This article references information from a study published in Science Advances: Highly aquatic marine stem archosaur with soft tissue preservation