Float or sink: modelling the taphonomic pathway of marine crocodiles (Mesoeucrocodylia, Thalattosuchia) during the death–burial interval

Abstract

A taphonomic model is erected for a dataset of 19 Steneosaurus (Mesoeucrocodylia; Thalattosuchia) from the Toarcian Posidonienschiefer Formation (Lower Jurassic) of Germany. These were deposited in a quiet-water, marine, basin. Their taphonomy is compared with that of an additional seven thalattosuchians from other Jurassic localities (Peterborough and Yorkshire, UK; Nusplingen, Germany). The skeletal taphonomy of the specimens is assessed in terms of the articulation and completeness of nine skeletal units. Steneosaurus from the Posidonienschiefer Formation exhibit variable levels of articulation in the nine units. Completeness also varies but the head, neck and dorsal units are complete in all specimens. Carcasses reached the sediment–water interface shortly after death. Loss of fidelity occurred primarily as individuals lay on the sediment, and disarticulated elements tended to remain in the vicinity of the carcass. Those elements absent from specimens are the smaller, more distal, bones of the limbs and tail; these were removed preferentially by weak bottom currents. Smaller specimens are consistently less complete. Specimens from other localities broadly follow the same taphonomic pathway, suggesting a consistent pattern for the skeletal taphonomy of the carcasses of marine crocodiles. Loss of completeness in some specimens is more exacerbated, the result of stronger current activity at the sediment–water interface.