COMPARISON OF PLEISTOCENE AND MODERN ROOT TRACES ON MAN HEAD CAY, SAN SALVADOR ISLAND, BAHAMAS, AND IMPLICATIONS FOR PLANT BIOGEOGRAPHY OVER TIME

The main objective of this research is to describe and interpret root traces in the Cockburn Town Member of the Grotto Beach Formation (Pleistocene) located on Man Head Cay, a small island (150 X 400 m) off the east coast of San Salvador Island, Bahamas. One of the methods used to achieve this objective was to compare these trace fossils to exposed root structures of modern plants in the same area, both on Man Head Cay and the northeast coast of San Salvador. Because root trace fossils represent the only fossil record for terrestrial plants on San Salvador, this study should give unique insights on how plant assemblages changed through time in this part of the Bahamas. Previous researchers documented abundant and well-preserved root traces in Pleistocene deposits on San Salvador, but in most instances these trace fossils have not been allied with specific tracemakers. Moreover, root trace fossils on San Salvador have not been described in accordance with botanical categories of roots (e.g., seminal, adventitious, first-order lateral, and so on); this procedure is done for the first time here. Through a comparison of ancient and modern root morphology using botanical descriptive methods, interpretations regarding the origins of the root trace fossils allow for more accurate determinations of the probable tracemakers. As a result, this study will examine the possibility of whether root traces on Man Head Cay can be attributed to modern species of plants that currently inhabit either Man Head Cay or nearby North Point. Alternatively, root trace fossils could have been made by species similar to those that are now extinct in this part of the Bahamas. North Point has been separated from Man Head Cay by shallow-marine shelf environments since the Holocene transgression began, disconnecting them for at least the past 5,000 years. This situation means that plant species were isolated well before human habitation, and thus trace fossils should represent species that were originally native to the main part of San Salvador but later became restricted to Man Head Cay.