Abstract

A detailed analysis of 813 tests of the irregular echinoid Fibularia sp. collected from multiple depositional horizons at a single Oligocene locality on South Island, New Zealand revealed 57 specimens with drill holes, representing a 7% drilling frequency (57 drilled individuals). Among those drilled, 38% (22 individuals) had multiple drill holes with up to four holes present. Most holes were complete, circular to sub-circular in outline, averaging 0.5 mm in diameter, and belong to the ichnospecies Sedilichnus simplex. The distribution of holes on the test was non-random: 1) the aboral surface was drilled preferentially, and 2) the central region of the aboral surface had a significantly higher number of holes (p < 0.005) than expected. No evidence of size selectivity was detected: the relationship between drill hole size and test size of Fibularia was not significant (p > 0.1). The distribution of drill holes as well as their shape and size make it likely that they were produced by a predatory gastropod, such as the cassid Galeodea that is known from the Oligocene of New Zealand. However, the high frequency of multiply drilled Fibularia allows for the possibility of a parasite, such as the eulimid Niso, another New Zealand gastropod coeval with Fibularia. This study adds to the growing body of literature on the drilling of echinoids, shedding light on the ecology of this group.

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