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| Lijiangosaurus yongshengensis W. Wang, Shang, J. Wang, Zi & Li, 2025 Artwork by Kelai LI |
Abstract
A long neck is a morphological innovation in vertebrates, particularly iconic in many plesiosaurs, while the function of these long necks in plesiosaurs remains controversial. Here, we report Lijiangosaurus yongshengensis gen. et sp. nov. from a previously unknown early Middle Triassic locality in southwestern China. This taxon represents the earliest known sauropterygian evolving an exceptionally long neck with 42 cervical vertebrae, and is identified as a nothosaur rather than the immediate ancestors of plesiosaurs. Our discovery demonstrates that extreme cervical elongation developing more than 30 cervical vertebrae emerged in sauropterygians prior to the rise of plesiosaurs and their pistosaur ancestors. Furthermore, Lijiangosaurus possesses a unique type of accessory intervertebral articulation compared with other reptiles, and we attribute this structure to reducing body undulation. This discovery increases the known diversity of accessory intervertebral articulations in reptiles, and underscores the high plasticity of the vertebral column in the early evolution of sauropterygians.
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| Type specimen (YSBB208) of Lijiangosaurus yongshengensis nov. gen. et sp. Image of the skeleton on a large block of limestone (a); interpreted illustration of the skeleton with different osteological parts labeled and marked in multiple colors (b); cv is the abbreviation of cervical vertebra; reconstruction of the complete skeleton in strict accordance with the preserved morphology in corresponding colors (c); scale bars equal 10 cm. |
Systematic paleontology
Reptilia Linnaeus, 1758
Diapsida Osborn, 1903
Sauropterygia Owen, 1860
Nothosauria Baur, 1889
Emended definition: Referred to the phylogenetic hypotheses recovered in this paper, the maximum clade definition of Nothosauria is reformulated as follows: all taxa more closely related to Brevicaudosaurus jiyangshanensis, Germanosaurus schafferi, and Nothosaurus species than Keichousaurus hui, Simosaurus gaillardoti, or Corosaurus alcovensis.
Composition: Based on the phylogenetic hypotheses in this study, Nothosauria includes Brevicaudosaurus jiyangshanensis, Germanosaurus schafferi, Lijiangosaurus yongshengensis, Wangosaurus brevirostris, and all the species of Nothosaurus and Lariosaurus.
Diagnosis: Nothosauria is a clade distinguished from other eosauropterygians by a combination of the following characters: dorsal exposure of prefrontal reduced, pineal foramen displaced posteriorly, mandibular articulation approximately at the level of the occipital condyle, diastema between premaxillary and maxillary teeth present, and four or more sacral ribs.
Lijiangosaurus yongshengensis gen. et sp. nov
Etymology: Both the generic and species names refer to the fossil site of Yongsheng County, Lijiang City, Yunnan Province, China. This currently only known specimen of this genus and species is the first Mesozoic reptile collected from this area.
Diagnosis: A medium-to-large-sized nothosaurian distinguished from other nothosaurians by a proportionally small skull with body length over 2.5 m (smaller than a few species of Nothosaurus like N. giganteus and N. mirabilis, but larger than most nothosaurian taxa), a remarkably high count of 42 cervical vertebrae, a dorsal neural spine comparable to the corresponding centrum in height (distinctly shorter than N. mirabilis, but longer than all other nothosaurians), entepicondylar foramina lost, accessory intervertebral articulation of infraprezygapophysis and infrapostzygapophysis present in dorsal and anterior caudal vertebrae. It can be further distinguished from non-nothosaurian eosauropterygians (especially pistosauroids) by the absence of interpterygoid vacuity, a ventral flange along the ventromedial edge of the quadrate ramus of the pterygoid, well-developed and extending further posteriorly up to the quadrate, an obturator foramen opening in the adult, and other synapomorphies of nothosaurians.
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| Phylogenetic relationship of Lijiangosaurus yongshengensis nov. gen. et sp. with other sauropterygians. The topology is based on a strict consensus tree from the 16 most parsimonious trees using an updated morphological character dataset from [Wang, et al. 2022]. Lijiangosaurus yongshengensis is the sister group of Wangosaurus brevirostris, both belonging to Nothosauria but not Plesiosauria. |
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| Reconstruction of nothosaurs about 240 million years ago revealing a hidden diversity from southwestern China. Taxa include Lijiangosaurus yongshengensis (central), Nothosaurus yangjuanensis (upper left), Nothosaurus luopingensis (upper right), Brevicaudosaurus jiyangshanensis (lower left), and Lariosaurus hongguoensis (lower right). All these nothosaurian taxa lived in the Middle Triassic in Yunnan and Guizhou provinces (Artwork by Kelai Li). |
Wei Wang, Qinghua Shang, Jiansheng Wang, Hongke Zi and Chun Li. 2025. Earliest Long-necked sauropterygian Lijiangosaurus yongshengensis and Plasticity of Vertebral Evolution in Sauropterygian marine reptiles. Communications Biology. 8, 1551. DOI: doi.org/10.1038/s42003-025-08911-1 [1 November 2025]
