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| Dianmeisaurus mutaensis Hu, Li & Liu, 2024 |
Abstract
After the devastating Permo-Triassic Mass Extinction, several new groups of large reptilian predators invaded the sea in the early part of the Triassic. Among these predators, sauropterygians, consisting of placodonts, pachypleurosaurs, nothosaurs and pistosaurs (including the iconic plesiosaurs), displayed the greatest diversity at both the generic and species levels, and persisted from the Early Triassic to the Late Cretaceous. Here, we report a new species of Pachypleurosauria, Dianmeisaurus mutaensis sp. nov., from a recently discovered Lagerstätte in the Upper Member of the Anisian Guanling Formation. The only known specimen of the new species was collected from a quarry near Muta village, Luxi County, Yunnan Province, South China. Our new phylogenetic analysis based on a novel data matrix recovered the new taxon as a sister group to Dianmeisaurus gracilis—a small pachypleurosaur from the Middle Triassic Luoping biota. The new phylogenetic analysis also collapsed the monophyly of the traditionally recognized Eusauropterygia. Pistosauroidea, Majiashanosaurus, and Hanosaurus comprise the consecutive sister groups to a new clade including Pachypleurosauria and Nothosauroidea. A monophyletic Pachypleurosauria, within which the clade consisting of Dianmeisaurus and Panzhousaurus occupies the basal-most position, is recovered by this study. The clade consisting of Dawazisaurus and Dianopachysaurus forms the sister group to the remaining pachypleurosaurs included in this study. Since Dianmeisaurus, Panzhousaurus, Dawazisaurus, and Dianopachysaurus are all exclusively known from South China, our study provides further evidence to the hypothesis that pachypleurosaurs had a palaeobiogeographic origin in the eastern Tethys.
Keywords: Marine reptiles, Pachypleurosauria, Dianmeisaurus, Phylogeny, Palaeobiogeographic origin
Systematic palaeontology
Sauropterygia Owen, 1860
Eosauropterygia Rieppel, 1994
Pachypleurosauria Nopcsa, 1928
Dianmeisaurus Shang & Li, 2015
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| The holotype of Dianmeisaurus mutaensis sp. nov. (HFUT MT-21-08-001). A the skeleton in dorsal view; B the counterpart of A (natural mold). Scale bars equal 1 cm |
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| The skull of Dianmeisaurus mutaensis sp. nov. (HFUT MT-21-08-001). A photo; B, interpreted drawing. an, angular; ar, articular; ata, atlas arch; atc, atlas centrum; axc, axial centrum; bo, basioccipital; c3, 3rd cervical centrum; d, dentary; eo-op, exoccipital-opisthotic complex; f, frontal; fo, fontanelle; j, jugal; m, maxilla; n, nasal; p, parietal; par, prearticular; pm, premaxilla; po, postorbital; pof, postfrontal; prf, prefrontal; q, quadrate; r3, 3rd cervical rib; sa, surangular; so, supraoccipital; sq, squamosal. The red arrow marks the pit on the premaxilla-maxilla suture. Scale bars equal 1 mm |
Dianmeisaurus mutaensis sp. nov.
Type locality: Muta Village, Luxi County, Yunnan Province, China.
Type horizon: Upper Member of Guanling Formation, Anisian, Middle Triassic.
Etymology: Named after Muta village where the holotype was collected.
Diagnosis: A pachypleurosaur with following autapomorphies among pachypleurosaurs: 23 cervical vertebrae, 20 dorsal vertebrae, and two sacral vertebrae; postfrontal extending posteriorly to a level beyond the middle of parietal; last dorsal rib stout and shorter than the first sacral rib; phalangeal formula of manus and pes 2-3-4-4-2 and 1-2-3-4-3 respectively. In addition to the above-mentioned autapomorphies, Dianmeisaurus mutaensis also differs from D. gracilis in the following morphological characters: maxilla enters the external naris; anterior process of the frontal does not extend beyond the anterior margin of the orbit; postfrontal excluded from the upper temporal fenestra; coronoid process absent.
Yi-Wei Hu, Qiang Li and Jun Liu. 2024. A New pachypleurosaur (Reptilia: Sauropterygia) from the Middle Triassic of southwestern China and its phylogenetic and biogeographic implications. Swiss Journal of Palaeontology. 143. DOI: doi.org/10.1186/s13358-023-00292-4
