SEQUESTRICHNIA IN COMPLEX <i>OPHIOMORPHA</i> ISP. FROM LATE PLEISTOCENE GRAINSTONES IN THE BAHAMAS, WITH MODERN ANALOGUE COMPARISONS

Abstract An important scientific contribution of ichnological research is to expand knowledge of animal behavior through the study of trace fossils. Ophiomorpha isp. is the dominant trace fossil preserved in Late Pleistocene shallow-marine grainstones throughout the Bahama Archipelago. These large, distinctive, and complex burrows commonly display elements reflecting specialized activities. Pouchlike structures of Ophiomorpha from two Exuma sites are interpreted as sequestrichnia—in this case, chambers constructed by callichirid shrimp specifically for storage of seagrasses and algae as food resources. Two morphologies are recognized: structures with radiating arms and blunt endings, and rectangular forms with pairs of arms separated by a short tunnel. These morphologies compare closely with structures present in modern burrow casts of Neocallichirus maryae from shallow-marine sands in Graham’s Harbour, San Salvador Island. Additional structures, termed loops and nodes, were recognized in both modern casts and as trace fossils from the Harry Cay study site on Little Exuma. Previously reported carbon and nitrogen stable isotope analyses of callichirid soft tissues from San Salvador indicated that seagrass is a major food source for Bahamian callichirids, providing strong evidence for interpretation of the pouchlike Ophiomorpha structures as sequestrichnia. Establishing the presence of seagrass beds in Late Pleistocene shallow-marine grainstones from the Exumas provides useful supplemental information for more detailed paleoenvironmental interpretations. Finally, the literature on modern callichirids and other shallow-marine decapod crustaceans includes numerous burrow diagrams illustrating structures that presumably were constructed for food storage. Additional sequestrichnia and other structures reflecting specialized activities within fossilized callichirid burrow systems likely will be discovered in the future.