2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 166-7
Presentation Time: 3:15 PM


GRUN, Tobias B., University of Tübingen, Department of Geosciences, Sigwartstraße 10, Tübingen, 72076, Germany, tobias.grun@uni-tuebingen.de

Although most sand dollars live their entire live burrowed in the sand and are completely covered by spines, they are subject to numerous lethal and sub-lethal predatory attacks. Well-known predators of these clypeasteroid echinoids include crabs, echinoderms, fish as well as predatory snails. Since these predators can leave distinct predation traces on the echinoid test, they can potentially be recognized in both modern and ancient environments while other predation events remain undetected due to the lack of distinct traces. In this study, numerous dead tests of the six-hold sand dollar Leodia sexiesperforata from San Salvador Island, The Bahamas are analyzed for changing predatory pressures during its life history. Test size range from 0.52 cm to 8.43 cm and show non-allometric growth with respect to test length and test width. The insertion of lunulae during growth can be clearly seen with the anal lunula always present.

Change in predatory pressure can be observed during sand dollar ontogeny. Dead denuded juvenile individuals were often found in high numbers lying directly on the sediment surface and mostly lacked any predatory traces which can result from crushing and drilling predation. Sub-adult and adult tests from the same area, however, often showed distinct crushing patterns which can be interpreted as fish predation. Juvenile tests also rarely feature predatory drillholes as produced by snails which can also be seen in larger individuals. 76 % of the tests larger than 3 cm show predatory drillholes, 50 % of the tests larger than 3 cm additionally show healed predatory activity on the test margins, produced by either fish or crab predation. Echinoids can suffer and survive a variety of these non-lethal predatory attacks. Predatory drillholes, however, never showed any evidence of healing and even unfinished drillholes can lead to the death of the individual.