Taphonomic losses become taphonomic gains: an experimental approach using the rocky shore gastropod, Tegula funebralis

The gaps in the fossil record are not liabilities for paleontologists but rather assets for evolutionary and paleoecological studies. The fossil record of rocky shore invertebrates is deemed poor, resulting from the bias of a high energy (physical) environment. The poor fossil record of the Pleistocene rocky shore gastropod Tegula funebralis appears to be no exception to this rule. However, field studies, including experimentally deployed shells in two habitats, reveal five important taphonomic processes that affect the resultant fossil resource for these gastropods: (1) the predilection for Tegula shells by the intertidal hermit crab, Pagurus samuelis, affects the longevity of the shells, (2) hermit crab-occupied shells of Tegula have a distinct array of bionts distinguishable from the living snail and empty, experimentally tethered shells, (3) biont types on tethered shells differ between two habitats (mudflat and rocky intertidal), and are thus useful for paleoenvironmental determinations, (4) physical processes greatly affected intact shell longevity of experimental shells at the rocky intertidal site, whereas at the mudflat site, mistaken predation by durophagous crabs was the most important agent of shell destruction, and (5) despite these taphonomic losses, the Pleistocene fossil record of Tegula retains a good record of the biological factors that affect its preservation, that of pagurid crustaceans and their gastropod shell-associated bionts. Taphonomic losses when viewed from a hierarchy of shell users, then, are gains in biological information that indicate the level of complexity within the shell-using community, and this record is not completely lost in high energy regimes.