EXPERIMENTAL TAPHONOMY OF DECAPOD CRUSTACEANS: ASSESSING THE EFFECTS OF PRE-BURIAL PROCESSES

The extent of the fossil record varies between different groups of decapod crustaceans, extending back to the Cretaceous for marine crabs and to the Pleistocene for terrestrial crabs. Previous studies of fossilization processes have focused on long-term taphonomic filters and on the effect of burial in sediments. However, many processes (e.g., waves, bioturbation) affect decapod remains on the surface before they are incorporated into the sediment. This study used gecarcinid (land) crabs in a series of experimental studies to elucidate how pre-burial processes control the disarticulation of decapods.

A total of 36 Gecarcinus lateralis and 12 G. ruricola specimens were deployed for two weeks at three localities along the north coast of San Salvador Island and in a controlled laboratory setting. The field sites differed in water depth, wave energy, vegetation density, and bioturbation intensity. Rates of disarticulation varied significantly across the three localities: highest rates were observed at the deepest, most densely vegetated locality and lowest at the shallow sandy flat. Minimum time for full disarticulation was two days, but crabs in the shallow sandy flat retained limbs for thirteen days. Scavenging and bioturbation were more important than wave/current energy in influencing the rate of disarticulation. Specimens in the lab remained completely articulated for up to 12 days, although they disarticulated when disturbed.

Legs were the first part to both separate and disarticulate at all localities. The lab experiments and the field observations consistently show that claws remained articulated for longer than either the carapace or the legs, an observation that is consistent with the relative overrepresentation of claws reported in the fossil record. Carapaces, important to crab taxonomy, became brittle and thin and were often fragmented and/or removed entirely due to scavenging and wave energy. The results of this study show that crabs, particularly claws, can survive the early phase of pre-burial processes. Fossilization of the more fragile elements, such as the carapace, however, may require rapid burial to ensure preservation.