World-class dinosaur fossil communities recreate unsolved mysteries or fill in gaps in evolutionary sequences

Pu'an Township, Yunyang County, Chongqing City, where "the world's largest Jurassic original site single-dimensional stone wall" was discovered, recently discovered a new large plant-eating dinosaur, Puxian Emei Dragon. But new discoveries don't stop here. A new "dinosaur mystery" recently surfaced in Pu'an Township. During conservation excavations, researchers have found that dinosaur fossils are also found in strata that are older than the layer where the fossil wall is located. What is more exciting is that the newly discovered dinosaur fossils may fill the gap in the evolutionary sequence of dinosaurs from the late early Jurassic to the middle Jurassic.

Chongqing Yunyang Pu'an dinosaur fossil group includes the Xintiangou Formation and Shaximiao Formation dinosaur fauna, which belong to the early Early Jurassic to Late Middle Jurassic stage in chronology, and dinosaur fossils from this period have rarely been found worldwide before. The Puxian Emei Dragon discovered in the Shaximiao Formation of the Yunyang Dinosaur Fauna is the second time that a new species of dinosaur was found in Yunyang after the discovery of two new species of Modaoxi Three Gorges Dragon and Pu'an Yunyang Dragon in the Xintiangou Formation of the Pu'an Dinosaur Fossil Group in Yunyang, Chongqing. The Puxian Emei dragon found in this study is a dinosaur individual with about 40% preservation, and "Puxian" is a species name, which belongs to the genus Emei. Fossil specimens found include partially preserved vertebrae, forelimbs, and hind limbs, as well as separately preserved materials such as collarbones and ribs.

The researchers found that the fossils unearthed from Puxian Emeilong were obviously different from the currently known Emeiosaurus, with their own unique characteristics, such as all the anterior vertebrae posterior convex, the central cervical vertebrae with complex air cavity structure, the dorsal lateral recess separated by secondary septums, the anterior caudal nerve spiny end extending backwards, the humeral deltoid crest pointing to the posterior lateral side, and the ratio of ulnar to humerus was 0.69. After restoration, Puxian Emeilong was an adult large plant-eating dinosaur with a body length of about 16 meters and a height of more than 8 meters from the ground when standing.

Tan Chao, a researcher at the Chongqing 208 Geological Relics Conservation Institute, said that Emeilong is one of the main representative dinosaurs in the Middle Jurassic, and the discovery of a new species of Emeilonga in Yunyang, Chongqing, indicates the expansion of the distribution range of Emeilong, and at the same time enriches a tax group of Emeilong, which is of great significance for studying the evolution and migration of Emeilongs.

The Pu'an dinosaur fossil group in Yunyang, Chongqing, originated from a bone-like stone found by a young local farmer in Laojun Village, Pu'an Township, in January 2015. After identification and site survey, experts who heard the news believed that there may be a huge group of dinosaur fossils from the Jurassic period hidden in the area. After two years of excavation and protection, the world's rare 150-meter-long monolithic dinosaur fossil wall was detected in Pu'an Township. This fossil wall includes 17 fossil-rich communities, and under the fossil wall there are also a large number of dinosaur fossils buried at a depth of more than 20 meters. What is even more surprising is that the Yunyang dinosaur fossil outcrop spans 4 townships and spreads along the stratigraphic direction for about 15 kilometers. After conservation and excavation, the world's largest and most distinctive Jurassic original site large-scale monolithic stone display wall officially appeared in front of the world in 2017, and the Chongqing Yunyang Pu'an Dinosaur Fossil Group was also identified as a world-class dinosaur fossil group by the National Paleontological Fossil Expert Committee that year.

Chongqing is one of the important dinosaur fossil burial sites in China, but many previous dinosaur fossil excavation sites are single locations, single skeletons of a single era or scattered fossils, and there are no groups of multi-species dinosaur fossils collectively buried in one location. The current excavations of the Pu'an Dinosaur Fossil Group in Yunyang, Chongqing have exposed nearly 10,000 fossils, including basal sauropods, sauropods, theropods, birdfoots, stegosaurus, as well as invertebrate fossils represented by aquatic reptile fossils such as plesiosaurs and turtles and bivalves.

Why are so many dinosaur fossils densely buried together? Xu Xing, a researcher at the Chinese Academy of Sciences, believes that 180 million to 160 million years ago, the Yunyang area was on the edge of the ancient lake (Cuban Shu Lake), and the swarms of different kinds of dinosaurs living on the lakeside died in one or more sudden disasters, and a large number of dinosaur bones drifting with the water precipitated down to form fossils when the flow rate of the river into the lake delta slowed down. Therefore, the Chongqing Yunyang Pu'an Dinosaur Fossil Site belongs to the "off-site cluster burial", which is the corpse of many dinosaurs who died in different places, and was "transported" to the same area by mudslides and floods. This also explains why the fossil arrangement within the fossil group is relatively disordered, and the age span is particularly large, and dinosaur fossils are distributed in many strata in the early, middle and late Jurassic.

Current research and excavations have shown that Yunyang, Chongqing, is another large dinosaur concentration in the southwest region after Zigong in Sichuan and Lufeng in Yunnan. Relevant departments are planning to build a "Jurassic Park" with the Pu'an Dinosaur Fossil Group in Yunyang, Chongqing as the core, so that more tourists can experience dinosaur-themed adventure tours at the Dinosaur Museum and Dinosaur Fossil Relics Museum in the park.

Column Editor-in-Chief: Gu Wanquan Text Editor: Yang Rong Title Image Source: Visual China Photo Editor: Shao Jing