Amazing graze – Grazing traces of sea urchins on turtles – An example from the Late Jurassic of Switzerland

Carapaces of marine turtles from the Late Jurassic Solothurn Turtle Limestone (Reuchenette Formation, Late Kimmeridgian) commonly yield rounded pits that may have resulted from epibionts or ectoparasites, although a conclusive interpretation has not yet been presented. Out of a large collection, only very few specimens of carapaces display areas that are more or less densely covered by stellate v-shaped grooves. These are attributed to the ichnotaxon Gnathichnus pentax Bromley and are interpreted as gnawing and rasping traces of the teeth of hemicidaroid sea urchins. The size of the traces suggests that Hemicidaris mitra (Agassiz) which is a very frequent and autochthonous part of the fauna was the producer of these stellate grooves. The grazing traces suggest the presence of a post-mortem dense algal cover and indicate an extended exposure time of the carapaces at the sediment-water interface.