Abstract

The land snail fauna from cave sediments in wet tropical lowland forest in central Jamaica was analyzed with regard to their implications for the biogeographic history of the late Quaternary. Eight radiocarbon dates on the shells range from 600 to 45,000 yr B.P. and show a close relationship to amino acid epimer ratios (D-alloisoleucine/L-isoleucine, or A/I, values). A/I values of individual shells indicate that the faunas span a continuous time sequence but that a significant mixture of ages occurs within each level of the cave sediments. The chronologies of individual species were therefore determined by A/I values of individual shells, calibrated against radiocarbon ages. The land snail fauna consists of 40 species (all endemic to the island) and shows remarkable stability over the span of time covered by the deposit, indicating the continuous persistence of forest. The much lower epimerization rate for the late Pleistocene compared to the Holocene indicates much cooler late Pleistocene temperatures, but this appears to have had little effect on the fauna. Many species that are presently endemic to restricted regions, which include the area of the cave, are present throughout the sequence. No changes are detected at the last glacial maximum, but some changes are seen in the Holocene. At 3000-4000 yr B.P., two species disappear from the sequence (one lives nearby at present, whereas the other presently has a distribution farther to the west). The first records of one species in the sequence occurs at this time, and for another species at ca. 10,000 yr B.P. No extirpations of species occur at the site following European settlement. Relatively stable climatic gradients, rather than climatic change, may be an important cause of the evolution of faunas endemic to different parts of the island.

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