Death, decay and disarticulation: Modelling the skeletal taphonomy of marine reptiles demonstrated using Serpianosaurus (Reptilia; Sauropterygia)

Taphonomic models for fossil vertebrates are designed to reconstruct processes that affected carcasses during the transition from biosphere to geosphere, in particular in the interval between death and burial. To circumvent various limitations in existing methodologies, a new taphonomic method, assessing vertebrate skeletons as nine anatomical units (the head, neck, dorsal, tail, ribs and four limbs) scored independently for two characters (articulation and completeness), was developed. The potential of the method is demonstrated using the Triassic marine reptile Serpianosaurus from Monte San Giorgio, Switzerland. Specimens are preserved in alternations of black shale and dolomite, representing normal background sediment and event beds respectively, deposited into a shallow, intra-platform basin. All specimens exhibit disarticulation of skeletal elements though loss of completeness varies considerably. Minor loss of fidelity occurred during the ‘floating phase’, but individuals reached the sediment-water interface relatively soon after death, and largely intact, where they decayed during the ‘residence phase’. Carcasses allowed to reach extensive states of decay became prone to the effects of weak bottom currents, resulting in removal of elements. The episodic deposition of event beds rapidly buried individuals at various stages of decay, inhibiting further disarticulation and loss of completeness.

► We model vertebrate taphonomy using an innovative new method.
► The method identifies the ‘phases’ responsible for loss of fidelity after death.
► The intrinsic and extrinsic processes causing variation can thus be investigated.
► Minor loss in Serpianosaurus was whilst floating, but most was in situ on the seabed.