Geographical heterochrony: Comtemporaneous coexistence of neogene and recent molluscan faunas in the Americas
Abstract Geographical heterochrony is a biogeographical pattern that, within a single faunal province, represents the contemporaneous coexistence of newly-evolved faunas and those which have persisted, unchanged, from earlier geological ages. This array of discrete, adjacent, and asynchronous faunules produces a mosaic pattern in both time and space. Based on the faunas of three anachronistic subregions within the Recent Caribbean Molluscan Province, one off the Yucatan Peninsula, one off Roatan Island, and one near the Gulf of Venezuela, this geographically heterochronous province is shown to contain two types of relict pockets. The term “primary relict pocket” is proposed for a faunule that contains the same genera and species as the older, more extensive parent fauna, and differs only in being reduced spatially. The term “secondary relict pocket” is proposed for a faunule that contains relict genera that were once widespread but have persisted and speciated within the boundaries of the pocket. Based on the faunas of the Caribbean relict pockets, on patterns seen in the fossil record, and on the unusual ecological conditions of the Gulf of Venezuela area, a new reconstruction of Neogene Caribbean molluscan provinciality is proposed and two new Neogene molluscan provinces, the Caloosahatchian and the Gatunian, are described. To explain the existence of the Caribbean relict pockets and their affinities to the Recent Panamic and Neogene Floridian faunas, a new interpretation of Upper Pliocene biological catastrophism and extinction is proposed, incorporating aspects of the effects of the closing of the Isthmus of Panama and glacially-induced sea level fluctuations and temperature changes. A new scheme of Recent tropical American marine molluscan provinciality is presented, taking into account the two paleoprovinces and the distribution of the post-Pleistocene Caribbean fauna.