The footprints of Jurassic carnivorous dragons found in Yan’an, Shaanxi Province, presumably up to 8 meters long
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The main authors of the paper include Associate Professor Xing Lida, China University of Geosciences (Beijing), University of Colorado Denver, USA Professor Martin G. Lockley, Liu Xuefeng, Zhang Zhisheng, and Hui Ruirui of Xingzichuan Oil Production Plant of Yanchang Oilfield in Shaanxi Province, etc., published the paper in this issue of “Historical Biology”.
In August 2020, Hui Ruirui, an employee of the Exploration Section of the Xingzichuan Oil Production Plant of Yanchang Oilfield, Shaanxi Province, and Ma Lang and Li Xinwei, staff of the Yanchang Petroleum Group Research Institute, were surveying oil near Majiagou Village in Ansai District. Dinosaur footprints were unintentionally discovered when the outcrop stratum distribution and sedimentary structure phenomenon occurred in the area. In December of the same year, Xing Lida’s research team from China University of Geosciences (Beijing) went to the site to investigate with the support of the oil production plant. A series of vertebrate footprints were confirmed and newly discovered in Ansai Liugou ridge, including theropod footprints and turtle swimming traces. , Ancient vertebrates and insect relics and other ancient biological relics.
Liugoujiao The footprint point is located at the top of the upper section of the Middle Jurassic Zhiluo Formation. The Zhiluo Formation is widely distributed in the Ordos Basin and is a sedimentary product of a typical arid climate. The whole is sedimentary fluvial clastic rock with a thickness of 100–200 meters. The vertebrate footprints of Liugoumao are located on a rock, preserved on a layer of ocher, light yellow-green-fine-grained sandstone, including 5 isolated dinosaur footprints and 6 isolated turtle footprints, and can be observed at the same time To mud cracks, wave marks and invertebrate remains fossils.
The theropod footprints found are three-toed with sharp toe marks, although the aspect ratios of the two well-preserved footprint specimens are significantly lower than the classic Eubrontes footprints, and It has a wider interdigital angle, but due to the small number of specimens and poor preservation, it is impossible to make a finer division. Scholars classified it into the Eubrontid family. Inferred from the size of the footprints, at least two theropods of different sizes have passed by and left marks on the footprint. According to calculations, the body lengths of the tracers are 8.1 meters and 6.5 meters respectively. The size of the former is very large. Close to large theropod dinosaurs, such as Allosaurus and Megalodon.
Liugoujiao The most important discovery of the footprint point is a batch of tortoise footprints, all turtle footprints are preserved as convex footprints, and are three-toed or four-toed claw marks, 2.3–11.4 cm in length, and toe marks usually appear as extended claw marks , The angle between the toes is so small that it is almost zero-the claw marks are almost parallel to each other. Generally speaking, most of the elongated scratches are interpreted as paw prints left by floating or swimming animals when they swim in the water. The tracers may be crocodiles, turtles, etc. However, the claw-like traces of Liugoumao are connected in an arched structure and resemble webbed feet. This is obviously different from the footprints of crocodiles, so they are classified as turtle-and-turtle footprints.
Mesozoic tortoise footprints are generally divided into two categories: Chelonipus and Emydhipus. Previously, scholars classified all the relics containing swimming traces as the Characichnos relics. However, the tortoise footprints were not included in the relics of the scratched footprints, and due to the special paleogeography and paleoenvironmental reasons, the country has not included the traces of tortoises. One of the elements that constitute the remains of the scratched footprint is not found—the Hatcherichnus crocodile swimming trace. In China’s lake deposits, fossil assemblages of turtle swimming traces have been found many times. Therefore, we have proposed a new relic facies-the turtle footprint relics facies. The relic communities that include turtle swimming traces can be classified here. .
Theropods The footprints of dinosaurs and tortoises appeared at the same time as the footprints of Liugoumao, that is, the combination of the footprints left by terrestrial and aquatic quadrupeds traveling in different ways (walking and swimming) at the same place, representing two different relic phases. The intersection of biological behavior and ancient environment in the same area. The co-occurrence of Liugoumao is the intersection of the selenosaurus footprint relic community and the newly defined turtle footprint genus.
In addition, a variety of invertebrate remains fossils have been found in Liugoumao, including: living and eating traces of decapod crustaceans-marine traces, burrows of annelids, broom worms or insects Traces-stone needle traces, burrows of polychaetes or other invertebrates, and traces of gastropods or crustaceans, etc.
Xing Lida, an expert in footprint science, said that based on past fossil footprint records, it can be inferred that a highly diverse fauna of dinosaurs appeared in northern Shaanxi during the Middle Jurassic, including Anomoepus and Anomoepus. Ornithischian dinosaurs represented by Deltapodus, and medium-large theropods, Kayentapus and Eubrontes. The discovery of the Liugoumao footprint point added larger theropod footprints and turtle footprints to the footprint fauna.
In short, the appearance of the largest footprint specimen of Liugoumao confirmed the existence of large theropod dinosaurs in the area during the Middle Jurassic. Fossils of footprints dominated by theropods and rich in theropods in the Jurassic and Cretaceous strata of China are very common. It is only in recent years that the Mesozoic tortoise footprints in China have been discovered one after another. Compared with the theropod footprint records across the entire Mesozoic, most of the previous tortoise footprint fossils came from the newer Cretaceous strata. Therefore, the Liugoumao swimming track in this study is currently the oldest tortoise footprint in China. In addition, the simultaneous appearance of the footprints of theropod dinosaurs and tortoises represents a complex situation where the two relics overlap. The proposal of the relic facies/remains community of sea turtle footprints will help to classify and analyze the relic facies of Chinese lakes in the future