Nanshiungosaurus

Extinct genus of reptiles

Nanshiungosaurus (meaning "Nanxiong's lizard") is a genus of therizinosaurid that lived in what is now Asia during the Late Cretaceous of South China. The type species, Nanshiungosaurus brevispinus, was first discovered in 1974 and described in 1979 by Dong Zhiming. It is represented by a single specimen preserving most of the cervical and dorsal vertebrae with the pelvis. A supposed and unlikely second species, "Nanshiungosaurus" bohlini, was found in 1992 and described in 1997. It is also represented by vertebrae but this species however, differs in geological age and lacks authentic characteristics compared to the type, making its affinity to the genus unsupported. It was a large sized therizinosaurid that is estimated to have cover nearly in length and to have weighed about Nanshiungosaurus had a very pneumatized vertebral column with the posterior cervical vertebrae of the long neck being unusually robust and slightly more elongated than the dorsals. It was equipped with a broad torso as seen on the bulky pelvis. As for other therizinosaurids, it had a keratinous beak used when feeding, stocky feet with four weight bearing toes and large flattened claws. Nanshiungosaurus is classified as a therizinosaurian dinosaur. Along with Therizinosaurus and Segnosaurus, Nanshiungosaurus was one of the earliest therizinosaurs to be described and named. The unusual shape of the pelvis led Dong—the original describer—to interpret the remains as belonging to some dwarf sauropod, but during the 1990s the genus was recognized as a segnosaur (now therizinosaur) based the pelvic similarities with Segnosaurus. At first, the research on therizinosaurs was complicated since sparse remains were known at the time and these had features from multiple dinosaur lineages leading to their interpretation as prosauropod dinosaurs.

In 1974, during a geological expedition at the Nanxiong Basin led by the Institute of Vertebrate Paleontology and Paleoanthropology several fossilized remains of dinosaurs were discovered by the team. Near the village of Dapingcun at the Nanxiong Formation, Guangdong Province, a relatively large and partial skeleton was found in articulation dating back to the Late Cretaceous. The specimen was labelled under the number IVPP V4731 and consisted of 12 cervical (lacking the atlas), 10 dorsal, 5 (actually 6) sacral and the first caudal vertebrae with a nearly complete, bulky pelvis only lacking the right ilium and ischium. Later on, in 1979 the specimen was formally described by the Chinese paleontologist Dong Zhiming and used as the basis for the new genus and species Nanshiungosaurus brevispinus. The generic name, Nanshiungosaurus, refers to the site of provenance Nanxiong city and is derived from the Greek σαῦρος (sauros, meaning lizard). Lastly, the specific name, brevispinus, is derived from the Latin brevis and spina (meaning short and spine, respectively) in reference to the relatively short vertebral spines. When first described, Dong mistakenly thought the specimen to have been a dwarf, strange titanosaurine sauropod characterized by a shorter but thicker neck than other sauropods based on the pelvis structure. In 1997 Dong Zhiming and You Hailu named and described a supposed second species: "Nanshiungosaurus" bohlini, based on a skeleton found in 1992 near Mazongshan. It consists of 11 cervical and 5 dorsal vertebrae with some ribs. The specimen is catalogued as IVPP V11116 coming from the Early Cretaceous, Upper Xinminbao Group. Also, they coined the Nanshiungosauridae to contain "both species". Dong and Yu presented no evidence or argumentation supporting the assignment of the species to Nanshiungosaurus. In 2010, the North American paleontologist Lindsay Zanno considered this referral to be highly improbable since "N". bohlini dates back from the Barremian Aptian ages and in the view of lack of synapomorphies, she considered that the supposed second species is unrelated to Nanshiungosaurus and might warrant its own genus. In addition, she corrected the number of sacral vertebrae from 5 to 6 and noted that the holotype pelvis from the latter has suffered damage since collection and has been reconstructed with painted plaster in the affected areas. Moreover, the remains of "N". bohlini were recovered from the lower red beds of the Zhonggou Formation in the Gongpoquan Basin, a completely different geological context. As an overall consensus, this dubious specimen is no longer considered to be relatable to Nanshiungosaurus.

Nanshiungosaurus was a relatively large bodied therizinosaurid, estimated at long weighing This taxon can be differentiated by the possession of stocky posterior most cervical vertebrae with opisthocoel (meaning that they were concave on their posterior sides) centra. Though the holotype specimen lacks cranial material, the preserved elements in therizinosaurids Erlikosaurus and Segnosaurus indicate that it had a relatively small skull with coarsely serrated teeth, and developed a prominent rhamphotheca (keratinous beak).

Most cervicals have relatively short neural arches, but in the dorsals they are more elongated. The axis is well preserved and has a length of with platycoelus (slightly concave at both ends) centra. Its odontoid process is fused with the anterior facet of centrum and has a blunt depression to the bottom area in order to articulate with the atlas centrum. The neural arch is narrow, the neural spine has a posterior orientation, and has rounded facets that connect with the atlantal posterior articular processes (bony projections). After the axis, the next cervicals gradually increase in size. The anterior cervicals have platycoelus centra and deep, pocket like pleurocoels (small holes) develop on the lateral sides; a small ridge like structure is also present. On the bottom surface, the centra are flat, gently flattened to the inner sides, and two projections originate from the borders of the centra. The anterior capitular process is compressed (flattened) with some degree of thickness, and extends from the bottom to lateral sides to be fused with the capitulum on the ribs. As for most cervicals, the neural arches and spines are short, the anterior articular processes are strongly developed in that direction, and the anterior lobes of the diapophyses (bony projections to the lateral sides) extend to the bottom and lateral directions to articulate with tubercles. Seventh and eighth cervicals are the longest with long centra and posterior to them, the vertebral size slightly narrows. In most posterior cervicals, the centra are opisthocoelous with shallow posterior grooves. After the findings of Nanshiungosaurus and Segnosaurus, more complete relatives started to be discovered, but their anatomical traits were so aberrant compared to other theropods to the point of being considered as Late Cretaceous sauropodomorph dinosaurs. In 1990, the paleontologists Rinchen Barsbold and Teresa Maryańska noted the striking similarities between the pelvises of Nanshiungosaurus and Segnosaurus, such as the ophisthopubic condition and large iliac blade. They concluded that the former was part of the Segnosauria and found this group to be a rare and aberrant group of saurischians in a position subject to change among sauropodomorphs and theropods. Dong also agreed with these similarities and placed the genus within the Segnosauridae in 1992. Nevertheless, the description of Alxasaurus in 1993 proved that the long aberrant segnosaurs were tetanuran theropod dinosaurs and Segnosauridae was a junior synonym of the older name Therizinosauridae. Segnosauria also became synonymous with Therizinosauria. In 1997, with the description and naming of "N". bohlini, Dong and You placed the therizinosaurids Nanshiungosaurus and the former into a separate Nanshiungosauridae. They did not provide authentic traits or bases behind this new grouping. The extensive phylogenetic analysis conducted by Hartman and colleagues in 2019 based on Zanno's 2010 analysis, recovers Nanshiungosaurus in a more derived position than Neimongosaurus or Therizinosaurus. Below are the obtained results: This formation is mainly composed by purplish mudstones and siltstones, and was deposited in a floodplain environment, under a relatively warm, humid subtropical climate. Oviraptorid eggs are particularly common on the formation with at least five well preserved egg clutches. Moreover, a fossilized female oviraptorid with two eggs is known from the formation. The tracks of ornithopod dinosaurs are locally abundant at the Nanxiong region. The therizinosaurid Nanshiungosaurus was a bulky high browser in its ecosystem, However, it is possible that some of these oviraptorosaurs did not actually live together given the poor stratigraphic analysis of the formation. the sauropod Gannansaurus, and the very sparse remains of hadrosaurid dinosaurs such as Microhadrosaurus (now a nomen dubium).