ABSTRACT
Variations in levels of gastropod predation on the rich Australian Tertiary echinoid fauna have been studied to assess the impact of predation on patterns of evolution and extinction. Variations in predation levels were examined between major taxonomic groups; between species within faunas; between species in individual clades; and between shallow and deep water faunas. Also, the distribution of incisions on the test was examined to determine the diversity of cassid predators.
Paleocene to Early Oligocene echinoid faunas show little evidence of gastropod predation. The first substantial evidence of such predation occurred in the Late Oligocene. The appearance of gastropod predation correlates with the appearance of cassid gastropods in the Australian fossil record. A substantial increase in gastropod predation occurred in the Early Miocene, with some groups exhibiting greater than 50% mortality. There were high levels of predation on the spatangoid Eupatagus, but different species exhibit marked variations in the areas of the test that were preferentially attacked, suggesting predation by more more than one species. Clypeasteroids at this time show virtually no evidence of gastropod predation. A Late Oligocene to Late Miocene Lovenia lineage shows a progressive decrease in predation over time. This is attributed to evolution of successive species into deeper water habitats, which were regions of lower predation pressure. Deep water echinoid faunas, such as that from the Middle Miocene Rutledge Marl, show no evidence of gastropod predation. It is suggested that the decline in diversity of holasteroids and cassiduloids can be attributed directly to the high levels of predation. Niche replacement of cassiduloids by clypeasteroids may have arisen from lower levels of gastropod predation on clypeasteroids.
