The paleoecology and extinction of endemic tortoises in the Bahamian Archipelago

Abstract

No native species of tortoises ( Chelonoidis spp.) live today in the Bahamian (Lucayan) Archipelago (= The Bahamas + The Turks and Caicos Islands), although a number of species inhabited these islands at the first human contact in the late-Holocene. Until their extinction, tortoises were the largest terrestrial herbivores in the island group. We report 16 accelerator mass spectrometer (AMS) radiocarbon (14C) dates determined directly on individual bones of indigenous, extinct tortoises from the six Bahamian islands (Abaco, Eleuthera, Flamingo Cay, Crooked, Middle Caicos, Grand Turk) on five different carbonate banks. These 16 specimens probably represent six or seven species of tortoises, although only one ( Chelonoidis alburyorum on Abaco) has been described thus far. Tortoises seem to have survived on most Bahamian islands for only one or two centuries after initial human settlement, which took place no earlier than AD ~700–1000. The exception is Grand Turk, where we have evidence from the Coralie archeological site that tortoises survived for approximately three centuries after human arrival, based on stratigraphically associated 14C dates from both tortoise bones and wood charcoal. The stable isotope values of carbon (σ13C) and nitrogen (σ15N) of dated tortoise fossils show a NW-to-SE trend in the archipelago that may reflect increasing aridity and more consumption of cactus.