TAPHONOMY AND PALEOECOLOGY OF A JURASSIC ICHTHYOSAUR: SIMILARITIES AND DIFFERENCES TO MODERN WHALE FALLS

Bones of an ichthyosaur (Ophthalmosaurus sp.) from the Oxfordian (Upper Jurassic) Sandsfoot Formation, UK, and the associated invertebrate fauna were investigated to test the hypothesis that carcasses of Mesozoic marine reptiles hosted similar communities to modern and fossil whale falls. Bite marks on the bone surfaces indicate initial scavenging by fishes. Echinoid grazing traces (Gnathichnus pentax) indicate colonisation of the defleshed bones by algal or microbial mats. This is confirmed by the presence of micro-borings in the bones and microbially induced carbonates on the bone surface (clotted micrite). Pyrite framboids and peloidal fabrics within the bone spaces possibly indicate microbial decay of the bone organic compounds by sulphate reduction. Finally, numerous suspension feeding macro-invertebrates, free living close by or directly attached to the bones, indicate prolonged exposure and colonization of the carcass on the sea floor prior to final burial. In this marine reptile fall, as in whale falls, we recognise an initial ‘mobile scavenger stage’ and a final ‘reef stage’. The microbial signatures (clotted micrite, pyrite framboids and peloids) may indicate development of a sulphophilic stage, as in modern whale falls, even though no direct evidence for a chemosynthetic-based ecosystem (e.g. chemosynthetic bivalves such as lucinids and thyasirids) was found.