Ancient reptile with fossil internal organs discovered

A newly discovered ancient reptile from Southwestern China has revealed fossilized internal organs, including the stomach, liver, and intestines, marking one of the rarest finds in paleontology. The creature, named Austronaga minuta, lived approximately 245 million years ago during the Early Triassic period, near the equator east of the supercontinent Pangaea. This marine reptile, which predated dinosaurs, possessed robust forelimbs, reduced hind limbs, and preserved soft tissues beneath its ribs. The fossils were found in the Guanling Formation in Yunnan Province, part of the Tethys Sea region. These sedimentary layers formed around 245 million years ago, during the transition from the Lower to Middle Triassic. At this time, the area was characterized by rich marine ecosystems teeming with invertebrates, fish, and marine reptiles. Some of these creatures exhibited unusual hunting behaviors, which would appear strange to modern observers. Austronaga minuta is represented by a nearly complete skeleton preserved on two slabs of rock. The animal measured about 60 centimeters in length and had a slender, elongated body. It featured 18 cervical vertebrae, followed by 24 thoracic, two sacral, and 71 caudal vertebrae. Its forelimbs were transformed into large paddles, with broad, reinforced fingers and numerous small bones called phalanges. This feature, known as hyperphalangy, is commonly observed in fish-eating reptiles such as ichthyosaurs and plesiosaurs. However, it had not been previously documented among older archosauromorphs. The hind limbs of Austronaga were significantly reduced, and the pelvis had lost its attachment to the rib cage. This suggests a highly specialized adaptation for aquatic life. The upper arm bone was more than twice as long as the femur, indicating a powerful swimming mechanism. These anatomical features support the hypothesis that Austronaga was an efficient predator in its marine environment. Austronaga belongs to an early branch of the archosauromorph lineage, from which crocodiles, dinosaurs, and birds later evolved. Unlike true dinosaurs, Austronaga did not belong to this group. Instead, it lived several million years before the earliest representatives of the dinosaur clade. The closest relative, Dinocephalosaurus, also inhabited water but showed less specialization in limb structure. Within the broader family tree, Austronaga is closely related to Macrocnemus, a land-based species, and Tanystropheus, a long-necked marine reptile that occasionally ventured onto land. This relationship highlights the independent evolution of aquatic adaptations within the archosauromorph group. Previously, scientists believed that marine adaptations in this lineage were limited. However, the discovery of Austronaga challenges this view, suggesting that early members of the group developed complex traits suited for oceanic life. The dark structures visible under the ribs were examined using ultraviolet photography and scanning electron microscopy. Under UV light, these remnants stood out against the surrounding rock. The team identified them as traces of the stomach, liver, and digestive tract. Such preservation of soft tissue is extremely rare, typically requiring rapid burial in fine sediments, low oxygen conditions, and the presence of minerals that can replace organic material. This find provides critical insights into the evolutionary history of marine reptiles and their ability to adapt to aquatic environments. The study, published in the journal Science Advances, includes contributions from researchers such as Stephan Spiekman of the State Museum of Natural History in Stuttgart. The discovery underscores the complexity of early vertebrate evolution and the diverse strategies animals employed to thrive in ancient seas.