SNAILS EATING SEA-URCHINS – PREDATION PATTERNS ON THE ECHINOID ECHINOCYAMUS FROM THE OLIGO-MIOCENE OF EUROPE

Predation by cassid gastropods on echinoids is known to occur commonly in Recent environments. These gastropods produce a distinct borehole which potentially can be recognized in fossil echinoid assemblages. Echinocyamus, a minute clypeasteroid echinoid less than 1 cm in size, is a common member of Recent and Cenozoic shallow water echinoid assemblages. They can be very numerous, occur in a very wide variety of depths and habitats, and often show signs of predation.

In this study, fossil Echinocyamus assemblages from the Oligo-Miocene of Europe are studied with respect to population dynamics and predation patterns and are compared with data from Recent settings. Numerous fossil Echinocyamus specimens show holes passing through the test. These interpreted boreholes rarely reach sizes larger than 1 mm. They are slightly irregular in shape corresponding to the presence of minute plates and numerous pores in the skeleton of the echinoid prey. The holes are most often restricted to the top side of the test with a clear accumulation in the structurally weaker central area.

The large number of predated specimens allow for detailed statistically analysis within populations and among different localities. This study encompasses the morphology of boreholes, predation frequencies, site selectivity patterns and the prevalence of multi-predatory attacks. Predation patterns are also analyzed with respect to general population structures, depositional environments and stratigraphic age. The results are compared to predation data on echinoid predation through time and substantiate an increasing rate of predation rates on sea-urchins from the Cretaceous to the Recent.