Abstract
An important component of the Alpine vertebrate record of Late Triassic age derives from the Kössen Formation, which crops out extensively in the eastern Alps. Here, we present an isolated and only partially preserved large rib, which carries an osteoderm on a low uncinate process. Osteological comparison indicates that the specimen likely belongs to a small clade of marine reptiles, Saurosphargidae. Members of the clade are restricted to the western (today Europe) and eastern margins of the Tethys (today China) and were so far known only from the Anisian stage of the Middle Triassic. The assignment of the new find to cf. Saurosphargidae, with potential affinities to the genus Largocephalosaurus from the Guanling Formation of Yunnan and Guizhou Provinces, China, would extend the occurrence of the clade about 35 million years into the Late Triassic.
Highlights
The Upper Triassic Kössen Formation is a lithostratigraphic unit at the western end of the Austroalpine, the uppermost tectonic unit of the eastern Alps in Switzerland and adjacent areas in Germany, Austria, and Italy
Duffin & Furrer, 1981; Kühn, 1940), and a diverse marine reptile fauna including large to giant ichthyosaurs (Furrer, 1993; Karl et al, 2014; Zapfe, 1976), thalattosaurs (Müller, 2007), and sauropterygians; the latter mainly represented by placodont remains (e.g., Broili, 1920; Grüter, 2006; Kühn, 1940; Neenan & Scheyer, 2014; SchubertKlempnauer, 1975)
Based on a general curvature with a gentle concave and opposite convex margin, the larger bone fragment conforms to a thoracic rib, which would indicate that the articulation surface constitutes the gently expanding proximal end of a holocephalous thoracic rib
Summary
The Upper Triassic Kössen Formation is a lithostratigraphic unit at the western end of the Austroalpine, the uppermost tectonic unit of the eastern Alps in Switzerland and adjacent areas in Germany, Austria, and Italy. The lower part of the formation (the basal Alplihorn Member and the overlying Schesaplana Member), is highly fossiliferous. The shallow marine limestones and shales of late Norian to Rhaetian age yielded, besides many invertebrate fossils, a diverse vertebrate fauna (Furrer, 1993; Furrer et al, 1992). The latter are usually represented as isolated or mostly disarticulated skeletal remains (teeth, bones, scales), whereas articulated remains are overall rare (e.g., Grüter, 2006; Neenan & Scheyer, 2014). Phytosaurs (Furrer, 1993), pterosaurs (Fröbisch & Fröbisch, 2006; Stecher, 2008), and temnospondyl amphibians (HF, pers. obs.) are rare terrestrial faunal elements
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