Simosaurus gaillardoti (von Meyer 1842) was recognized as the sister taxon to the eusauropterygians (Nothosaurus, Lariosaurus, Pistosaurus). Here, derived from a sister to Lariosaurus and Nothosaurus, Simosaurus phylogenetically preceded Pistosaurus and Plesiosaurus.

Distinct from Lariosaurus, the skull of Simosaurus had a wider rostrum and was not so flat. The cheek area was more robust with a relatively smaller orbit. An elongated premaxillary ascending process separated the nasals from each other and contacted the frontals. The postorbital did not contact the parietal. The internal naris were circular. There were more cervicals and dorsals. The forelimbs were longer than the hind limbs. The radius, ulna and hand were relatively longer.

Paludidraco multidentatus (Chaves et al. 2018) is a sister to Simosaurus with a smaller, shorter and narrower skull, smaller and more numerous teeth, larger ribs and smaller limbs.

Wangosaurus brevirostris (Ma et al. 2015) originally Wangosaurus nested as a sister Yungisaurus (Figs. 2, 3) and both were considered pistosaurids, the clade transitional between nothosaurs and plesiosaurs, despite their morphological differences. Here Wangosaurus nests close to Simosaurus and Paludidraco, taxa that also have small teeth and a curved rostrum.

Chaves C de M, Ortega F and Pérez-García A 2018. New highly pachyostotic nothosauroid interpreted as a filter-feeding Triassic marine reptile. Biology Letters. 14 (8): 20180130

Ma L-T, Jiang D-Y, Rieppel O, Motani R and Tintori A 2015. A new pistosaurid (Reptilia, Sauropterygia) from the late Landinian Xingyi marine reptile level, southwestern China. Journal of Vertebrate Paleontology 35(1): e881832.

Meyer H von 1842. Simosaurus, die Stumpfschnauze, ein Saurier aus dem Muschelkalke von Luneville. Neues Jahrbuch fur Mineralogie, Geognosie, Geologie und Petrefakten-Kunde 1842:184-197.

Rieppel O 1994. Osteology of Simosaurus gaillardoti and the Relationships of Stem-Group Sauropterygia. Fieldiana Geology New Series No. 28. online pdf

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