Grazing activity as taphonomic record of necrobiotic interaction: A case study of a sea turtle carapace from the Upper Jurassic of the Prebetic (south Spain)

Abstract

Bioerosion trace fossils can shed light on the ecological interactions between species. Here we describe an unusual case of bioerosion on a turtle carapace of Hispaniachelys prebetica from the Oxfordian (around 155 Ma, Upper Jurassic) of the Prebetic (Betic Cordillera, South Spain). The specimen was found in a limestone bed of a marl-limestone rhythmite. Morphological analysis of the bioerosive structures reveals the dominance of epigenic traces produced by the grazing activity of regular sea urchins (ichnospecies Gnathichnus pentax). No other bioerosion structures are present. From an ethologic point of view only epigenic traces (pascichnia) are present. Gnathichnus pentax records short-term bioerosion produced exclusively on the carapace before its burial. The ichnological assemblage recorded herein typifies the Gnathichnus Ichnofacies. The carapace was the most favourable hard substrate for grazers in comparison to the surrounding muddy soft bottom. The carapace was oriented convex-down when found in the rock. Therefore, pascichnial activity probably occurred early after the death and accumulation on the sea floor of the turtle remains, but before the carapace was overturned by large scavengers. The low degree of fragmentation and the low dispersion of skeletal components indicate a low-energy environment and early burial in the sea bottom.