The Nothosaurs of the Southern German Lettenkeuper (Triassic, Late Ladinian)

Abstract

The order of Nothosauria belongs to the superorder of Sauropterygia, a group of extinct marine reptiles. Nothosaurs formed, together with ichthyosaurs, the top of the food chain of Triassic marine ecosystems. Except for two sauropterygian species from North America, the distribution of sauropterygians in general and nothosaurs in special was limited to the coastlines of the Tethys sea and the Germanic Basin, which formed one of the main habitats of nothosaurs. Until now, it was assumed that the main diversification of nothosaurs in the Germanic Basin took place during the fully marine Muschelkalk (Anisian) and that the diversity of this group decreased during the Lettenkeuper (Ladinian) due a regressive trend leading to sea-level lowstands and a subsequent drying up of the Germanic Basin beginning in the northern part of the basin. In this work, new nothosaur finds from the from the Lettenkeuper are presented. They shed a new light on the diversity and temporal distribution of nothosaurs in southern Germany. During own excavations in the Lettenkeuper sediments of Vellberg-Eschenau close to Schwäbisch Hall in 2017, a completely preserved skull of a new Nothosaurus species was discovered. In a detailed publication, the new find was described as Nothosaurus cristatus. Detailed drawings as well as an own phylogenetic analysis were made and N. cristatus was embedded in the existing phylogenetic tree of nothosaurs. This find is of great relevance because it shows that the diversity of Nothosaurus species during the Lettenkeuper was higher than previously expected. In a second publication, the occiput of a Nothosaurus skull was described. It was recovered during a salvage excavation in the Lettenkeuper of Kupferzell in 1977 and erroneously described as skull part of the archosaurian reptile Batrachotomus kupferzellensis in 1999. This publication contains the re-description of the occiput as Nothosaurus giganteus based on comparisons with other nothosaurs, detailed comments about the stratigraphy of the find location, and drawings of the found skull elements. This find underlines that large nothosaurs still existed in the already strongly regressionally affected Germanic Basin during the time of the Lettenkeuper and that the marine influence in present-day southern Germany was bigger than previously expected.