NON-LETHAL TRACES OF PREDATION IN TESTS OF RECENT AND FOSSIL ECHINOIDS
This pilot study included 148 sand dollar specimens collected at four sites on the shallow shelf of the northeastern Gulf of Mexico and included three species: Encope michelini (n=33), Mellita tenuis (n=52), and Clypeaster subdepressus (n=63). Cuspate shaped marks along the ambitus of the tests, and on some specimens extending into the lunules, were observed on many specimens. We interpret these as traces produced by non-lethal triggerfish predation. The traces never extend into the petals, which suggests that bite marks involving petals are more likely to be lethal. There appears to be species selectivity, and traces were more frequent on the flatter sand dollars, Encope michelini (88%) and Mellita tenuis (65%), and rare on Clypeaster subdepressus (21%).
In addition, fossil sand dollars from the Pliocene portion of the Tamiami Formation were examined for marginal traces. Healed traces comparable in morphology to those observed on live-collected specimens were observed on fossils tests of Encope tamiamiensis, Mellita aclinensis, and Clypeaster sunnilandensis, which suggests the presence of non-lethal predation.
An expanded analysis including both recent and fossil echinoids will aid in the recognition of and development of protocols to identify non-lethal predatory traces, and better understand the relationship between the predators causing the traces and their echinoid prey in the fossil record.