The norian Plateosaurus bonebeds of central Europe and their taphonomy

Abstract

Plateosaurus is probably the single most common dinosaur in the Late Triassic, known from over 40 localities in the Norian Knollenmergel mudstones of central Europe. In addition, it is also one of the best known Triassic dinosaurs due to the discovery of many complete skeletons. These complete skeletons as well as the majority of all other material are actually derived from only a handful of localities, three of which are compared here to one another in detail. Frick (northern Switzerland), Trossingen (southwestern Germany), and Halberstadt (central Germany) are recognized as the result of the same taphonomic processes and can all be described with the term “ Plateosaurus bonebed”. This type of bonebed is characterized by its large size, measured in thousands of square meters, the large number of incomplete and complete Plateosaurus skeletons, and the lack of other vertebrate fossils, with the exception of the primitive turtle Proganochelys. The uniformly upright carcass position precludes post mortem transport and strongly argues for in situ death. Shallow depressions in the thick floodplain muds of the Knollenmergel must have formed efficient traps for the heaviest animal at that time, Plateosaurus. The animals became mired and were scavenged upon by small theropods whose shed teeth are always present in Plateosaurus bondebeds. Miring explains the deep position of the feet and hindquarters and, in combination with scavenging and weathering, the bias towoards bones of the posterior body region. The lack of juvenile individuals is due to their lower foot pressure, which was below the threshold for becoming mired.