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.

RAREIN SITUPRESERVATION OF ADULT CROCODYLIAN WITH EGGS FROM THE MIDDLE EOCENE OF GEISELTAL, GERMANY

“…The articulation and completeness of the adult skeleton of GMH 6074, and indeed many of the crocodylians of Geiseltal, are reminiscent of wellpreserved skeletons of marine crocodyliforms of the Jurassic Posidonienschiefer Formation of Germany (Beardmore et al 2012). An assessment of the completeness and articulation of GMH 6074 following the standards created for these crocodyliforms has been provided in Table 1.…”

“…The heavy amount of dermal armor in the dorsal and anterior caudal sections of the body prevents full assessment of completeness and articulation of these portions of the axial skeleton. Further classification of taphonomy has been designated in a study of carcass decay in modern Crocodylus (Syme and Salisbury 2014), following the units established by Beardmore et al (2012). This classification defines inter-unit articulation, presented for GMH 6074 in Table 2.…”

Revision of Saurorhynchus (Actinopterygii: Saurichthyidae) from the Early Jurassic of England and Germany

“…Sedimentation rates for the serpentinum Zone are estimated at an average of 2 mm compacted sediment / kyr at the Holzmaden locality (Martill 1993), an order of magnitude less than that of the Besano Formation and potentially explaining the much lower frequency of complete specimens and skull units associated with opercles, or even mandibles, in the Posidonienschiefer Formation. Additional loss of completeness may be related to current activity (Hofmann 1958;Brenner & Seilacher 1978;Kauffman 1978Kauffman , 1981Riegraf et al 1984;Beardmore et al 2012;Reisdorf et al 2012;Beardmore & Furrer 2016a).…”

The Slottsmøya marine reptile Lagerstätte : depositional environments, taphonomy and diagenesis

“…Bottom currents can be responsible for the disarticulation of skeletons and loss of skeletal elements (Beardmore et al 2012a), and the position of skeletal elements can be used to evaluate water movement and direction of flow (Barnes & Hiller 2010). Small light bones have the highest potential to be moved by currents.…”