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Qianjiangsaurus; Temporal range: Late Cretaceous PreꞒ Ꞓ O S D C P T J K Pg N
	Life restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Neornithischia
Clade:	†Ornithopoda
Clade:	†Hadrosauriformes
Superfamily:	†Hadrosauroidea
Genus:	†Qianjiangsaurus; Dai et al., 2024
Species:	†Q. changshengi
Binomial name
	†Qianjiangsaurus changshengi; Dai et al., 2024

Qianjiangsaurus (meaning "Qianjiang lizard") is an extinct genus of hadrosauroidean ornithopod dinosaurs from the Late Cretaceous Zhengyang Formation of China. The genus contains a single species, Q. changshengi, known from a partial skeleton. Qianjiangsaurus is one of the few hadrosauroids named from south China, and it indicates important fauna connections between similarly aged formations in Mongolia.

Discovery and naming

The Qianjiangsaurus holotype specimen, CLGRP V00016, was discovered by a paleontological expedition associated with the Chongqing Bureau of Geological and Mineral Resource Exploration and Development during the winter of 2022. The locality represents sediments of the Zhengyang Formation near Zhengyang area in Qianjiang District, Chongqing Municipality of southwest China. The specimen consists of a partial, somewhat articulated skeleton, comprising an incomplete mandible, four dorsal vertebrae, the sacrum, many caudal vertebrae and associated chevrons, most of the pelvic girdle, and several hindlimb bones.^[1]

In 2024, Dai et al. described Qianjiangsaurus changshengi as a new genus and species of hadrosauroid dinosaurs based on these fossil remains. The generic name, Qianjiangsaurus, combines "Qianjiang"—the name of the district containing the type locality—with the Greek σαῦρος (sauros), meaning 'lizard'. The specific name, changshengi, Changsheng Wang, the discoverer of the Chongqing fossil locality.^[1]

Nanningosaurus, a genus from the Nalong Basin of Guangxi, is the only other hadrosauroid currently named from south China.^[1]^[2]

Description

The holotype of Qianjiangsaurus likely represents a mature adult individual. It is medium-sized in comparison to related taxa, at about 8 metres (26 ft) long.^[1]

The prepubic process of the pubis is fan-shaped, with a length:height ratio of about 0.79, representing the single autapomorphy (unique derived trait) identified in the holotype. The unique combination of other characters includes a total of 30 dentary tooth positions with no more than five teeth per alveolus (tooth socket), a coronoid process at a right angle to the dentary, and seven fused vertebrae in the sacrum. While some of its plesiomorphic (ancestral) anatomical features confidently place it within the Hadrosauroidea, it still demonstrates apomorphic (derived) features of later-diverging members of the Hadrosauridae, placing it as a transitional form between the two groups.^[1]

Classification

In their phylogenetic analyses, Dai et al. (2024) recovered Qianjiangsaurus as the sister taxon to the Mongolian Plesiohadros of the Djadokhta Formation,^[3] with these taxa as late-diverging members of the Hadrosauroidea outside of the Hadrosauridae. Their results are displayed in the cladogram below:^[1]

	Zuoyunlong

	Probactrosaurus

Tanius

	Plesiohadros

	Qianjiangsaurus

	Telmatosaurus

	Tethyshadros

	Lambeosaurinae

	Saurolophinae

Paleoecology

The discovery of Qianjiangsaurus provides further support for several faunal similarities between the Zhengyang Formation of China and the Djadokhta and Baruungoyot formations of Mongolia. These dinosaur parallels may indicate a faunal interchange between the two regions during the end of the Late Cretaceous, from the late Campanian–early Maastrichtian. While absolute dates have yet to be determined for the Zhengyang Formation, it was likely deposited during this time.^[1]

Qianjiangsaurus is the first distinct dinosaur taxon to be named from the Zhengyang Formation. Fragmentary specimens belonging to unnamed titanosaurs and theropods (including tyrannosauroids and putative carnosaurs) have also been found. Since large-scale excavations had not occurred in the region until 2022, additional specimens—such as ornithomimosaurs, therizinosauroids, oviraptorosaurs as seen in coeval formations—may be found in the future.^[1]^[4]^[5]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h Dai, Hui; Ma, Qingyu; Xiong, Can; Lin, Yu; Zeng, Hui; Tan, Chao; Wang, Jun; Zhang, Yuguang; Xing, Hai (2024-08-27). "A new late-diverging non-hadrosaurid hadrosauroid (Dinosauria: Ornithopoda) from southwest China: support for interchange of dinosaur faunas across East Asia during the Late Cretaceous". Cretaceous Research (in press): 105995. doi:10.1016/j.cretres.2024.105995. ISSN 0195-6671.
^ Mo J.; Zhao Z.; Wang W.; Xu X. (2007). "The first hadrosaurid dinosaur from southern China". Acta Geologica Sinica (English Edition). 81 (4): 550–554. Bibcode:2007AcGlS..81..550M. doi:10.1111/j.1755-6724.2007.tb00978.x.
^ Tsogtbaatar, K.; Weishampel, D.; Evans, D. C.; Watabe, M. (2014). "A New Hadrosauroid (Plesiohadros djadokhtaensis) from the Late Cretaceous Djadokhtan Fauna of Southern Mongolia". In Eberth, D. A.; Evans, D. C. (eds.). Hadrosaurs. Indiana University Press. pp. 108−135. ISBN 978-0-253-01385-9.
^ Chen, Yang; Yin, Fuguang; Liu, Zixuan; Zhang, Ruigang; Li, Lianglin; Chen, Wei; Chen, Fei (2018). "渝东南正阳地区晚白垩世恐龙化石产出地层沉积环境特征" [Recent progress in the study of the sedimentary environment of Late Cretaceous dinosaur strata in Zhengyang area, southeastern Chongqing]. Geology in China (in Chinese). 45 (2): 414–415. doi:10.12029/gc20180217. ISSN 1000-3657.
^ Lin, Yu; Wang, Jun; Luo, Liangdong; Li, Deliang; Xiong, Can; Xiao, Ming; Zhang, Saike; Fang, Ruize; Yang, Daifeng (2024-04-19). "渝东南正阳盆地晚白垩世构造—沉积演化" [Tectonic and sedimentary evolution of the Late Cretaceous Zhengyang Basin in southeastern Chongqing, SW China]. Geological Review (in Chinese). 70 (2): 2024020018–2024020018. doi:10.16509/j.georeview.2024.04.022. ISSN 0371-5736.