Ancestral body plan and adaptive radiation of sauropterygian marine reptiles
Wei Wang,
Qinghua Shang,
Long Cheng,
Xiao-Chun Wu,
Chun Li
Affiliations
Wei Wang
Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; Centre for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China; State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing, China
Qinghua Shang
Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; Centre for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
Long Cheng
Wuhan Centre of China Geological Survey, Wuhan, China
Xiao-Chun Wu
Canadian Museum of Nature, Ottawa, ON, Canada
Chun Li
Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; Centre for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China; Corresponding author
Summary: Sauropterygia is the most diversified and dominant clade among marine reptiles, but their early evolution is scarcely understood. Here we report the earliest known complete specimen related to sauropterygians from the Early Triassic. It is referred to Hanosaurus hupehensis by an exclusive combination of features and shows mosaic morphology integrating the characters of multiple sauropterygian sub-lineages. In phylogenetic results from both parsimony and Bayesian analyses employing our reconstructed dataset, Hanosaurus is stably resolved as the basal-most member of Sauropterygiformes, a clade comprising all sauropterygians and saurosphargids. This skeleton reveals an unexpected ancestral body plan for sauropterygiforms with an elongate trunk and four short limbs, differing from many of its immediate descendants but more similar to non-sauropterygiform marine reptiles at their early aquatic stage as axial swimmers. After this convergence on body plan, we quantitatively confirm the rapid divergence of sauropterygiform reptiles following the end-Permian mass extinction.
