Scientists were able to discover and study the perfectly preserved digestive system of a marine reptile that inhabited Earth 245 million years ago. Specialists described an specimen of the archosauromorph Austronaga minuta, which existed in the Middle Triassic in the Yunnan province of China.
Analysis confirmed that this species belonged to the family Trachelosauridae and led a marine lifestyle. In addition to skeletal remains, this animal had fossilized skin, muscles, blood vessels, as well as stomach, small and large intestines, and liver preserved. According to a publication in the journal Science Advances, this is the oldest preserved reptilian digestive system.
Archosaurids and other archosauromorphs have repeatedly inhabited the oceans. Among the most successful representatives are seabirds and Mesozoic Thalattosuchians, which are distant relatives of crocodiles. Some of the first marine archosauromorphs were members of the Middle Triassic families Tanystropheidae and Trachelosauridae, belonging to the recently identified clade Tanysauria, such as Tanystropheus with their very long necks. It is assumed that the transition of these two families to oceanic life occurred independently.
A team of scientists led by Wayne Van from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences presented new data on the marine tanysaur Austronaga minuta. This small species was first described by Van and his colleagues in 2023 based on a fossil specimen from Yunnan province—a limestone slab containing a skull, part of the neck, and tail. The age of the find was determined to be 245 million years, corresponding to the Middle Triassic. Since A. minuta was found in marine deposits, and its nostrils were shifted back from the snout, and it had conical teeth in its mouth, the discoverers hypothesized that it fed on fish and lived in the sea.
In a subsequent study, Van and his team analyzed another limestone slab where missing parts of the same A. minuta specimen were found: a remnant of the neck (which turned out to be quite long), torso, limbs, and base of the tail. Analysis of the entire specimen confirmed the species' belonging to the tanysaurids, specifically the family Trachelosauridae. Its closest relative was Dinocephalosaurus orientalis, which also inhabited the seas of Yunnan at the same time.
Researchers, based on the complete skeleton of A. minuta, concluded that its length was only 60 centimeters, significantly smaller than the six-meter D. orientalis. However, it remains unclear whether an adult or juvenile specimen was studied. Scientists also found additional signs of a marine lifestyle: the forelimbs and hindlimbs, due to the proportions and structure of the bones (including elongated fingers due to extra phalanges), functioned as flippers for swimming. Furthermore, the scapula, coracoid, pubis, and ischium of A. minuta were thinned, resembling plates, which is characteristic of other marine reptiles. There was partial reduction of the pelvic girdle, which reduced its ability to support weight on land. It is likely that A. minuta swam excellently, using its tail for propulsion and its limbs as rudders, while its long neck helped it catch fish. Notably, its relative D. orientalis, despite living in the sea, did not have such strong adaptation to the aquatic environment.
The second limestone slab preserved soft tissues of A. minuta: remnants of skin and muscles in the sacral region, as well as the stomach, small and large intestines, liver, and blood vessels. Traces of undigested food, presumably fish scales, were found in the intestine, further confirming A. minuta's aquatic lifestyle. Nevertheless, overall, the internal organs of this species did not show a high degree of specialization for marine life. The authors emphasize that A. minuta represents the oldest reptile whose digestive system has been preserved to this day.
Previously, paleontologists established that the excessively long necks of tanystropheid archosauromorphs made them easy prey for predators. This is confirmed by fossil remains of two such reptiles, preserved only as heads and parts of cervical vertebrae. Predators likely attacked them from above and behind, using a powerful bite to sever the cervical vertebrae, after which they would drag the head with part of the neck and eat the rest of the body.
In a separate study, paleontologists discovered a tooth of the fossil spiny sunfish Neocometes brunonis in a German clay pit. The age of this find was estimated at 11.58 million years, which refutes the previous opinion that spiny sunfish had completely disappeared from Europe 1.7 million years earlier. The description of this find was published in the journal Fossil Imprint.
Researchers from Loma Linda University examined over three thousand dinosaur bones recovered from a deposit in Wyoming, United States, and managed to identify four pieces with markings attributed to the Tyrannosaurus rex.
The study, published in the journal PLOS One last Wednesday (15th), demonstrated that signs resembling bites can mislead even specialists. Factors such as diseases, decomposition processes, and the natural structures of the bones are capable of generating marks that imitate predator attacks.
Bethania C. T. Siviero and her team conducted this investigation with the aim of establishing methods to differentiate traces left by carnivorous animals from modifications resulting from natural phenomena.
The fossils analyzed come from the Lance Formation, located in northeastern Wyoming, an area that formed approximately 66 million years ago, at the end of the Cretaceous period. This site contains a large quantity of bones, predominantly belonging to the herbivorous dinosaur Edmontosaurus annectens.
Over two decades of excavations, thousands of fragments were collected from the deposit, forming a collection known as a bonebed, which contains remains of various species mixed together, without the configuration of complete skeletons.
Although the team sought evidence of predation, they found only 13 bones with any mark similar to a bite. After a more detailed inspection, only four exhibited characteristics consistent with the action of the T. rex.
The confirmation of the identification was based on comparing the patterns left by the teeth with the known characteristics of carnivores from that era. The most significant marks were small parallel scratches created by dental indentations.
According to Bethania C. T. Siviero, a paleontologist at Loma Linda University and project leader, it is crucial to recognize the correct origin of changes in bones to interpret the behavior of extinct animals. She clarified to Earth.com that surface marks can have multiple origins and require careful evaluation.
The team concluded that the spacing of the small protuberances on the teeth corresponded to the Tyrannosaurus rex, as other predators in the region possessed teeth with closer serrations, generating distinct patterns.
Among the fossils examined were a rib, a caudal vertebra, a piece of the spine, and a section of a forelimb. A second bone showed scratches similar to those of the T. rex, but lacked sufficient detail for definitive confirmation.
One of the most illustrative findings of the study involved a jaw fragment that initially appeared to have been attacked by a crocodile, due to a sequence of regular perforations resembling tooth marks.
However, analysis performed by computed tomography revealed a different explanation: the channels traversed the interior of the bone in several directions and connected, a characteristic compatible with natural structures that transported blood vessels and nerves while the animal was alive.
Additionally, it was verified that the material did not belong to Edmontosaurus, as initially thought. Comparison pointed to a similarity with the jaw of a young Torosaurus, a dinosaur belonging to the ceratopsid group, which includes Triceratops.
This incident highlighted how a mistaken interpretation can lead to incorrect conclusions about the interaction between ancient species, since a supposed crocodile bite on an herbivore would actually be an intrinsic anatomical feature of the animal itself.
The researchers also investigated the context of the marks found. The absence of any sign of healing suggested that the animals had likely already died before sustaining the observed damage.
Siviero explained to Earth.com that bones of animals that survived attacks would show signs of tissue regeneration. Since such signs were almost nonexistent, the researchers considered it more probable that predators consumed available carcasses.
Other elements at the same site corroborated this hypothesis: broken ribs near the ends, insect marks, and signs of climatic exposure indicate that the bodies were exposed on the surface for a period before being buried.
The frequency of tooth marks also varied between different fossil deposits. While a study in a deposit in Colorado, dated to about 150 million years ago, recorded signs on nearly one-third of the bones analyzed, the Wyoming site presented a proportion of less than 1%.
Based on the results obtained, scientists established specific criteria to determine whether a bone alteration truly corresponds to a bite. This analysis takes into account the shape, depth, edges, and location of the marks, as well as the anatomy of the suspected animal.
The purpose is to increase the credibility of inferences about the feeding habits and relationships between extinct species. A mistakenly classified mark can transform a natural alteration into false evidence of hunting or conflict between animals.
For the researchers, this study does not invalidate the theory that the T. rex fed on other dinosaurs, but rather demonstrates that such records are significantly rarer and more complex to recognize than previously assumed.
