INFORMATION LOSS IN THE ROCKY INTERTIDAL: THE IMPACT OF TAPHONOMY ON PALEOECOLOGICAL METRICS

Taphonomic processes are fundamentally processes of loss. Post-mortem, organisms experience constant attrition of information, such as loss of soft parts, loss of shell material, mechanical breakage, dissolution, and so on. Many of these processes reduce the amount of information that can be gathered from an organism’s remains. The recognition of when taphonomic damage has occurred as well as recognition of whether taphonomic processes lead to any systematic biases in paleoecological metrics is therefore critical.

This study quantifies changes to shell measurements (specifically length, thickness, width, dissolution, bioerosion, and encrustation) occurring as a result of taphonomic processes for the rocky intertidal snail Littorina littorea. We also assessed changes in our ability to recognize repair scars. We examined unmanipulated samples to determine whether there was a consistent relationship between increasing taphonomic scores and repair frequencies, calculated as the number of individuals with at least one repair scar. Repair scars form when organisms experience sublethal predation, and they are important tools for interpreting predatory regimes in both fossil and Recent assemblages. We also experimentally manipulated shells to quantify how shell measurements and repair scar recognition changed through time. We predicted that increasing taphonomic scores for dissolution, bioerosion and encrustation would correlate with:

1. Decreased repair frequencies as a result of a reduced ability to recognize repair scars
2. Reductions in shell length, width and thickness due to loss of shell material

We also predicted that changes would be progressive with increasing exposure to taphonomic processes. As anticipated, shells experienced significant loss of material. The relationship between repair scars and taphonomy, however, was less clear: increasing taphonomic damage may either obscure or reveal repair scars. Our study suggests that organisms showing evidence of transport should be excluded from paleoecological studies, as many metrics presumed to be ecologically important are likely to have changed post-mortem.