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A new long-snouted marine reptile from the Middle Triassic of China illuminates pachypleurosauroid evolution.

ABSTRACT: Sauropterygia is the largest, most successful group of Mesozoic marine diapsids, spanning from the late Early Triassic to the Late Cretaceous. Plesiomorphic for sauropterygians, pachypleurosauroids are important for our understanding on the early evolution of this group. Here, we present a new pachypleurosaurid, Luopingosaurus imparilis gen. et sp. nov., based on an exceptionally preserved skeleton from the early Middle Triassic Luoping Lagerstätte in Yunnan, China. The discovery documents the first long-snouted pachypleurosaurid with an unexpected hyperphalangy in the manus, providing new insights into the morphological diversification, ecological adaption and biogeographic evolution of this clade. The discovery further indicates that there is a morphological divergence between short-snouted (brevirostrine) keichousaurids and relatively long-snouted (longirostrine) pachypleurosaurids, which was probably driven by ecological specializations related to feeding and foraging. Additionally, an evolutionary trend towards the reduction of the ratio of the hyoid length to mandibular length (HM ratio) is recognized in pachypleurosauroids. This reduction of HM ratio, associated with the increase of the snout length, might implicate a gradual recession of suction feeding in pachypleurosauroid evolution. Phylogenetic studies incorporating Luopingosaurus recover European pachypleurosaurids as successive sister groups to Chinese derived pachypleurosaurids, supporting a western Tethyan origin for this family.

SUBMITTER: Xu GH

PROVIDER: S-EPMC9816097 | biostudies-literature | 2023 Jan

REPOSITORIES: biostudies-literature

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A new long-snouted marine reptile from the Middle Triassic of China illuminates pachypleurosauroid evolution.

Xu Guang-Hui GH Shang Qing-Hua QH Wang Wei W Ren Yi Y Lei Hong H Liao Jun-Ling JL Zhao Li-Jun LJ Li Chun C

Scientific reports 20230105 1

Sauropterygia is the largest, most successful group of Mesozoic marine diapsids, spanning from the late Early Triassic to the Late Cretaceous. Plesiomorphic for sauropterygians, pachypleurosauroids are important for our understanding on the early evolution of this group. Here, we present a new pachypleurosaurid, Luopingosaurus imparilis gen. et sp. nov., based on an exceptionally preserved skeleton from the early Middle Triassic Luoping Lagerstätte in Yunnan, China. The discovery documents the f ...[more]

PMID: 36604433

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Project description: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 Testudines 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.

Dataset Information

A new long-snouted marine reptile from the Middle Triassic of China illuminates pachypleurosauroid evolution.

Publications

A new long-snouted marine reptile from the Middle Triassic of China illuminates pachypleurosauroid evolution.

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