An armoured marine reptile from the Early Triassic of South China and its phylogenetic and evolutionary implications

Abstract

Sauropterygia was a taxonomically and ecomorphologically diverse clade of Mesozoic marine reptiles spanning the Early Triassic to the Late Cretaceous. Sauropterygians are traditionally divided into two groups representing two markedly different body plans - the short-necked, durophagous Placodontia and the long-necked Eosauropterygia - whereas Saurosphargidae, a small clade of armoured marine reptiles, is generally considered as the sauropterygian sister-group. However, the early evolutionary history of sauropterygians and their phylogenetic relationships with other groups within Diapsida are still incompletely understood. Here, we report a new saurosphargid from the Early Triassic (Olenekian) of South China - Prosaurosphargis yingzishanensis gen. et sp. nov. - representing the earliest known occurrence of the clade. An updated phylogenetic analysis focussing on the interrelationships among diapsid reptiles recovers saurosphargids as nested within sauropterygians, forming a clade with eosauropterygians to the exclusion of placodonts. Furthermore, a clade comprising Eusaurosphargis and Palatodonta is recovered as the sauropterygian sister-group within Sauropterygomorpha tax. nov. The phylogenetic position of several Early and Middle Triassic sauropterygians of previously uncertain phylogenetic affinity, such as Atopodentatus, Hanosaurus, Majiashanosaurus and Corosaurus, is also clarified, elucidating the early evolutionary assembly of the sauropterygian body plan. Finally, our phylogenetic analysis supports the placement of Testudinata and Archosauromorpha within Archelosauria, a result strongly corroborated by molecular data, but only recently recovered in a phylogenetic analysis using a morphology-only dataset. Our study provides evidence for the rapid diversification of sauropterygians in the aftermath of the Permo-Triassic mass extinction event and emphasises the importance of broad taxonomic sampling in reconstructing phylogenetic relationships among extinct taxa.

A new hupehsuchian (Reptilia: Ichthyosauromorpha) from the Lower Triassic of South China with implications for the evolution of polydactyly

“…Horizon, Age, and Locality-Third Member, Jialingjiang Formation, Spathian, Olenekian, Lower Triassic (see Wolniewicz et al [2023] for the discussion of horizon of fossiliferous beds). The specimen was collected from the Yingzishan Quarry (Li & Liu, 2020), Yuan'an County, Hubei Province, China.…”

“…The Mesozoic (252-66 Ma) saw the evolution of multiple successful lineages of marine predators (Kelley & Pyenson, 2015;Motani & Vermeij, 2021;Wolniewicz et al, 2023). Ichthyosauromorpha is one such group that emerged after the Permo-Triassic mass extinction (252 Ma) and rapidly occupied the marine predator niche during the Early and Middle Triassic (Motani et al, 2017;Qiao et al, 2022).…”