Postcranial material of Nothosaurus marchicus from the Lower Muschelkalk (Anisian) of Winterswijk, The Netherlands, with remarks on swimming styles and taphonomy

Abstract

The postcranial morphology of Nothosaurus from Winterswijk is described on the basis of three partially preserved skeletons. Because of the association with a diagnostic cranium, two of these can be confidently assigned to N. marchicus. Preserved humeri are recognized as morphotype II, which confirms the relationship between this humeral morphotype and N. marchicus. The occurrence of an additional nothosaur taxon in the Lower Muschelkalk, strong sexual dimorphism, or a broader size range of N. marchicus is evidenced again. The postcranial morphology of Nothosaurus is compared to published and new data on the basal pistosauroid (cf. Cymatosaurus) from the same locality. Numerous shared morphological characters of N. marchicus, Nothosaurus sp., and the basal pistosauroid from Winterswijk hamper assignment of isolated bones, which is presently only possible if a combination of features on multiple bones from a single individual can be assessed. Ontogenetic stage of the described skeletons is discussed as well. Differences between N. marchicus, the basal pistosauroid, and the morphologically similar, but smaller pachypleurosaur A. heterodontus are mainly related to the morphologies of the humerus, ulna, and the clavicle-interclavicle complex, and thereby indicate different modes of locomotion i.e., swimming styles. The pachypleurosaur and the basal pistosauroid were most likely anguilliform swimmers, whereas Nothosaurus also employed its forelimbs during swimming (paraxial swimming). Taphonomical observations on material of the Winterswijk locality indicate the presence of scavengers, although most disarticulated skeletons were transported by water and decayed and disintegrated in shallow water.

Diverse Aquatic Adaptations in Nothosaurus spp. (Sauropterygia)—Inferences from Humeral Histology and Microanatomy

“…Morphological details of nothosaur humeri were summarized by Rieppel, [ 1 ], Rieppel and Wild [ 9 ], Bickelmann and Sander [ 13 ], and Klein [ 12 ]. Specific taxonomic assignment of isolated Nothosaurus humeri is often impossible due to incompletely known association with diagnostic skulls and strong morphological variability, possibly involving sexual dimorphism as well [ 1 , 9 , 14 , 15 ]. Large Nothosaurus -type humeri also may belong to the large-bodied taxon Germanosaurus , which is based on two skulls but lacks associated humeri [ 1 ].…”

Conflicting evidence for the use of caudal autotomy in mesosaurs

“…The tail of pachypleurosaur nothosauroids is about the same length as the rest of the body and is not particularly dorsoventrally expanded 37 . Interestingly, nothosaurs are interpreted as utilizing both their tail and webbed limbs during aquatic locomotion 38 . The overall tail and limb morphology of nothosaurs is similar to what is observed for mesosaurs, which may suggest that mesosaurs may have also employed a type of locomotion similar to nothosaurs.…”

First Triassic tetrapod (Sauropterygia, Nothosauridae) from Castilla y León: evidence of an unknown taxon for the Spanish record

“…The non-pachyostotic centra and neural arches in UPUAM 14072 are shared with the genus Nothosaurus within the clade Nothosauria, as well as the presence of platycoelous centra (Bickelmann and Sander, 2008). Nothosaurus is a sauropterygian taxon known by several species, whose fossils have been found in the Middle and lower Upper Triassic of Europe, China, Israel and Tunisia (Rieppel and Wild, 1996;Rieppel et al, 1997;Rieppel, 2000;2001;Albers and Rieppel, 2003;Li and Rieppel, 2004;Albers, 2005;Jiang et al, 2006;Shang, 2006;Bickelmann and Sander, 2008;Klein and Albers, 2009;Liu et al, 2014;Klein et al, 2015). Within this genus, the species Nothosaurus giganteus Münster 1834, presents autapomorphic neural arches according to Rieppel and Wild (1996) and Rieppel et al (1999).…”