EXTANT AND EXTINCT CORALS ON A LATE PLIOCENE REEF TRACT FROM JAMAICA

Caribbean reef coral communities reach a diversity peak in the Plio-Pleistocene with a species pool 60% larger than that found in the modern Caribbean. Late Pliocene faunas include a mixture of regionally extinct species that co-existed with most of the species that persist to the present day. These mixed faunas contain the Stylophora and Caulastraea spp. that dominate earlier Neogene reefs as well as species of Acropora and Montastraea that are the key structuring species on modern Caribbean reefs. While the fact that these corals co-occur in Caribbean Plio-Pleistocene aged sediments is well known, the detailed ecological relationships between these extant and extinct forms is poorly understood.

We studied extensive new exposures in the Late Pliocene (~2 mya) Hopegate Formation of northern Jamaica. This unit is a well-dated, shallow water carbonate unit composed of coral-rich back reef, reef crest and fore reef facies and thus is ideal for an examination of coral associations in the Late Pliocene. We collected approximately 1500 specimens from localities across a 15 km outcrop belt and identified 64 species from the Hopegate Formation, including 25 extinct and 39 extant species.

Examination of species distributions and relative abundance reveals that the mean number of localities per species is significantly lower for the extinct forms, and a significantly higher proportion of the extinct species are rare in those samples in which they occur. Extinct species are also under-represented in localities containing abundant in-place reef corals. Thus, the extant portion of the Hopegate coral fauna was more widely distributed and abundant in our Late Pliocene collection localities. Among the extinct species, only Caulastraea is found in most sites collected. In the late Pliocene of Jamaica, Stylophora and most of the other corals that would become extinct in the Caribbean Pleistocene were comparatively rare and living in environments marginal to reefs dominated by essentially modern Caribbean reef communities.