THE TRACE FOSSIL DACTYLOIDITES OTTOI IN LATE PLEISTOCENE MARINE CALCARENITES OF THE BAHAMAS: PALEOENVIRONMENTAL AND PALEOECOLOGICAL IMPLICATIONS

The rosetted trace fossil Dactyloidites ottoi (Geinitz, 1849) recently was reported and described for the first time from late Pleistocene (MIS 5e) marine, shelly calcarenites on Great Inagua and Great and Little Exuma islands of the Bahama Archipelago. At all three sites, D. ottoi specimens are present on bedding planes at the top of shallowing upward successions that are capped by either late 5e eolianites or a hard caliche layer formed during the Last Interglacial.

While not common and not preserved in fine detail, the distinctive, fan-shaped morphology of the Bahamian specimens with radiating elements that commonly branch makes D. ottoi easily recognized and identified. Radial structures or “arms” likely emanated from a central shaft, as reported in previous studies, but examples of shafts were not found at our sites, probably because the Bahamian specimens are on bedding planes with minimal vertical exposure. In all other respects, these examples compare favorably in shape and size with D. ottoi specimens from other localities around the world, including the oldest well-documented specimens from the Jurassic of Argentina.

The tracemaker was most likely a polychaete, such as a lugworm, with the trace fossil interpreted as a fodinichnion formed by deposit-feeding activity. We favor the model of Wilmsen & Niebuhr (2014) for generation of D. ottoi-like traces by facultative feeding on marine-plant remains buried within the host sediment. The late Pleistocene paleodepositional environment of these carbonate sediments is interpreted as within the lower foreshore to upper shoreface zone in full marine, tropical waters supporting seagrasses and likely with marine algae washing in from offshore. This discovery of D. ottoi marks an addition to the Bahamian shallow-marine ichnocoenose within the Skolithos ichnofacies.

Given the young age of these Bahamian deposits, there is good reason to think that the tracemaker organism of Dactyloidites ottoi is alive and active today within the shallow-marine environments of the Bahamas and other similar settings of the wider Caribbean region. This provides opportunity for future discoveries, both of more examples of D. ottoi in the rock record and of its tracemaker organism(s).