Domination by Reptiles in a Terrestrial Food Web of the Bahamas Prior to Human Occupation
Human activities in the Bahamas and other oceanic islands have damaged terrestrial ecosystems irreparably through the extinction of indigenous species. Tortoise and crocodile bones from Abaco Island in the Bahamas sampled for 14C-dating revealed a small overlap between the last occurrence of these large reptiles and early human settlement in the Bahamas. Before their extermination approximately 1,000 years ago, the dominant herbivore and carnivore on Abaco Island were the endemic Albury's Tortoise (Chelonoidis alburyorum) and the formerly widespread Cuban Crocodile (Crocodylus rhombifer). Stable isotope data from carbon (δ13C) and nitrogen (δ15N) in bone collagen from Late Holocene fossils suggest that these large reptiles were part of a terrestrial rather than marine or estuarine food web. Our proposal that Cuban Crocodiles were once the apex terrestrial predator in the Bahamas is supported by comparisons with published δ13C values for modern marine/estuarine crocodylians as compared to those of nonmarine reptilian and mammalian carnivores. For reptiles to occupy terrestrial trophic roles distinguishes Bahamian Islands from nearby Greater Antillean Islands (Cuba, Jamaica, Hispaniola, Puerto Rico) where endemic mammals represent the largest herbivores and carnivores in prehuman times. This distinction is even greater when compared with Late Quaternary mammals of prehuman vertebrate communities in neighboring North America.Abstract
Western portion of the Bahamian Archipelago, with fossil sites noted. Thin gray line represents the 200-m isobath.
Exterior of Sawmill Sink, Abaco, Bahamas. Diver Brian Kakuk stands on the dive platform.
Fossils of the Cuban Crocodile, Crocodylus rhombifer, and extinct tortoise, Chelonoidis alburyorum, from Abaco, Bahamas. (A–D) NMB.AB50.021, adult skull of C. rhombifer in dorsal view (A), ventral view (B), lateral view with mandible (C), and lateral view without mandible (D). (E–G) NMB.AB50.0007, adult complete shell of C. alburyorum (with healed bite marks from the Cuban Crocodile) in lateral view (E, F) and dorsal view (G). (H) NMB.MY11.0001, adult partial carapace of C. alburyorum, with fully penetrating bite marks from the Cuban Crocodile. Scale bars = 10 cm.
Subset of representative bones from Sawmill Sink, Abaco, Bahamas, sampled for stable isotope collagen analysis. (A) Homo sapiens, NMB.AB50.0691, tibia. (B) Crocodylus rhombifer, NMB.AB50.0048, ulna. (C) Crocodylus rhombifer, NMB.AB50.0698, humerus. (D) Chelonoidis alburyorum, NMB.AB50.0008, humerus. (E) Crocodylus rhombifer, NMB.AB50.0029, radius. Scale bar = 10 cm.
δ 15N and δ13C isotopic values derived from collagen of 14 bone samples (Crocodylus rhombifer, Chelonoidis alburyorum, and Homo sapiens) from blue holes on Abaco and Andros, Bahamas (see data in Table 2).
Bahamian bone collagen isotopic values plotted against established guidelines for terrestrial- versus marine-derived food sources (Richards and Hedges, 2003).
δ 13C and δ15N-isotopic values derived from bone collagen plotted against known bone collagen isotopic values for terrestrial and marine organisms, including early human data from Puerto Rico. Isotopic data were compiled from three literature sources (Schoeninger and DeNiro, 1984; Keegan and DeNiro, 1988; Stokes, 2005). Values for crocodiles, tortoises, and Bahamian humans are all from this study.
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