Patterns of gastropod predation on middle Eocene echinoids from the western Eucla Basin, Western Australia

WA Museum Records and Supplements | Updated 6 months ago

ABSTRACT – Modern echinoids are known to suffer predation from a range of organisms, from fishes to gastropods and sea otters to birds. One of the most common evidence for such predatory behaviour in the fossil record comes from the ichnospecies Oichnus simplex Bromley, 1981, a small, straight-sided, circular hole which in the test of echinoids is interpreted as having been made by cassid gastropods. Such trace fossils provide good evidence for the temporal and geographical distribution of these gastropods in the past. Here we report such gastropod predation on a diverse middle Eocene echinoid fauna from bryozoal limestones in southwestern Australia. Of the 14 species of echinoids recorded, half show evidence of such predation. All are irregular echinoids that burrowed in the sediment to varying degrees. The percentage of echinoid specimens that suffered gastropod predation is 8.3%, varying between 6% and 16% of those echinoids for which there are statistically significant samples. The presence of what is interpreted as cassid predation on these middle Eocene echinoids is the earliest record in Australia and one of the earliest known in the evolutionary history of the group, marking the beginning of the expansion of this form of gastropod predation on echinoids.