Predatory Bore Holes
Predatory boreholes, which record the activity of naticid gastropods, were stereotypically located in the center of both left and right valves of C. cancellata. Boring frequencies varied widely from sample to sample. However, the distribution of boring frequencies in each paleoenvironmental setting are not significantly different. There is not a significant difference in the boring frequency between the paleocommunities even though the population sizes varied greatly between the two zones.
In the upper facies, which had more abundant C. cancellata, the larger valves were more likely to be bored than in the lower facies, where all size classes were bored equally.
Red: Samples in which bored C. cancellata were significantly larger than unbored C. cancellata
Black: Samples in which bored C. cancellata were larger than unbored C. cancellata, but not signficantly
White: Samples in which bored C. cancellata were smaller than unbored C. cancellata, but not signficantly
Epibionts
Modern C. cancellata are shallow burrowers, and usually have the posterior part of their shell protruding above the sediment. These exposed areas can often be found with algae or sea whips attached to them. Fort Thompson C. cancellata also have epibionts attached in life position, including corals and barnacles (above). Some were clearly post mortem infestations (e.g., the epibiont grew on the hinge teeth). The position of others indicate that both epibiont and clam lived together.
Barnacles
Red: Samples in which barnacles were found attached to C. cancellata
Black: Samples in which barnacles were not found attached to C. cancellata
Corals
Red: Samples in which corals were found attached to C. cancellata
Black: Samples in which corals were not found attached to C. cancellata
There were not any corals or baracles present on C. cancellata specimens from the lower zone (above), even though both corals and barnacles were found both loose and attached to other shells in that zone.
There could be a number of explanations for this pattern. One simple explanation could be that of since there are about ten times more C. cancellata in the upper zone, there is a greater chance for these rare occurrences to happen in that zone than in the lower zone. Dead C. cancellata valves were more common in the upper zone which could allow them to serve as a substrate for post-mortem infestations of epibionts. However, since there were not any coral infestations on C. cancellata in the lower zone, even after hundreds of valves were examined, this pattern is probably not just a chance happening.
Another explanation could be that under different paleoenvironmental conditions the burrowing behavior of C. cancellata was different. For instance, if lower zone clams burrowed slightly deeper into the sediment, the epibionts would be less likely to attach.
Other paleoenvironmental conditions could have altered the relation between C. cancellata and its epibionts. For instance if the bottom was choked with sea grass, or fouled with algae, the otherwise exposed posteriors of the C. cancellata would be covered. There is evidence that there were large, open bare sand patches during the time of upper zone deposition, and these more energetic bottom conditions could expose C. cancellata posteriors due to scouring.