CLAMS, WHELKS, AMPHIPODS, AND SHOREBIRDS: A NEOICHNOLOGICAL LOVE STORY

Neoichnology – the study of modern traces – is a wellspring of information for paleontologists seeking modern analogs of fossil behavior. However, modern trace assemblages showing behavioral interactions and responses between four or more species are relatively rare, let alone applicable to reconstructing local food webs. Therefore, I am pleased to share an example of how modern traces of intertidal bivalves, gastropods, and shorebirds from Jekyll Island (Georgia) can demonstrate such interactions while providing models for similar trace fossil assemblages.

The cast of trace-making characters are: dwarf surf clams (Mulinia lateralis); knobbed whelks (Busycon carica); amphipods (Acanthohaustorius spp.); sanderlings (Calidris alba); and laughing gulls (Leucophaeus altricilla). The chain of events connecting these species was started by the whelks, which buried themselves in saturated sands of a newly emergent intertidal zone. This burying liquefied sands around the large gastropods, which better allowed dwarf surf clams to burrow into these disturbed zones. Unfortunately for the clams, but fortunately for the sanderlings, this sedimentary situation concentrated them in visually prominent patches, which attracted roaming packs of sanderlings. Abundant beak-probe traces, vacant bivalve-shaped holes, and tracks around whelks attested to intense mining of the shallowly burrowed clams. Some whelk resting traces, though, lacked whelks. In these instances, laughing gulls further aided sanderling feeding. According to closely associated traces, gulls pried and pulled whelks from their hiding places to feed on them. These actions exposed infaunal amphipods underneath and around the whelks, which again attracted sanderlings, leading to dense concentrations of their beak-probe traces and tracks in and around whelk resting traces. In summary, trace fossils of similarly complicated relationships may be difficult to interpret at first, but are more likely clarified through neoichnology.