The fidelity of the fossil record for paleoecological studies often is questioned. This investigation attempted to determine how well communities of living benthic organisms are represented by the assemblages of dead remains accumulating in the sediment, i.e., future fossil assemblages.

Fifty quantitative samples were collected with a diver-operated suction dredge from various shallow-marine environments near Isla Cancun and Isla Contoy, Quintana Roo, Mexico. Virtually all the geologically preservable megafaunal remains in the sediment consisted of mollusks, and 290 molluscan species were identified in the samples. Although nearly three fourths of the species were collected only as dead shells, almost all live individuals were represented by dead shells of their species in the same sample.

A series of Q-mode and R-mode cluster analyses, utilizing 5 different similarity coefficients and data based on the presence or absence and relative abundances of species, demonstrates that the same general associations of samples and organisms occur, whether living animals or dead remains only are considered. Chi-square association tests between pairs of samples collected 5 m apart reveal that the death assemblages in both samples of each pair are similar, whereas the living communities are not.

The death assemblages apparently reflect the in-place accumulation of remains of living benthic communities during sedimentation as patchily distributed populations of organisms migrate across the bottom, leaving a record of their mortality behind them in the sediment.

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