PALEOGEOGRAPHIC VS BIOGEOGRAPHIC HYPOTHESES FOR THE ORIGIN OF THE CARIBBEAN BIOTA: THE DEBATE CONTINUES

In this presentation we consider some issues concerned with recent efforts to divine the history of the Caribbean realm and its biota via biogeography and paleogeography. A frequent form of argumentation in the biogeographical literature is to hold that, because some particular set of biological or paleontological data (including molecular clock dating) does not agree with a particular paleogeographical reconstruction, then the reconstruction must be wrong. The point that is missed in this line of argument is that paleogeography and biogeography are interrelated but independent sciences, each with its own merits and deficiencies, and each based on its own source of data. Paleogeography is the outcome of combining plate tectonics (time vs positioning of terranes) and stratigraphy (time vs environmental reconstruction, as in terrestrial, lacustrine, marine, etc.). The notion of “time” in plate tectonics is based on data sets (paleomagnetics, radiometric dating, paleontology of ocean sediments) that are usually different from those used to identify the age of constituent strata (which are instead stratigraphic position, paleontology, and, to a lesser degree, radiometric dating). Consequently, arguments against a given paleogeographical reconstruction ought to derive from a scrutiny of the validity of the specific data and interpretations involved. Furthermore, in order to avoid a circular argument, the dating tool used for the rocks should not be the same as the set of fossils used for biogeographical analysis. Another major problem is the poor understanding of paleogeography. Currently, plate tectonic reconstructions are focused on understanding the relative positions of tectonic plates, microplates and terranes at some moment in the past. Only rarely do plate tectonic maps display emergent or submerged environments, even when the data are easily acquired, and thus this information is unavailable for biogeographical purposes. Only special paleogeographic maps, designed for biogeographic purposes, can be of any use to this end. The debate over the GAARlandia hypothesis provides several examples of the difficulty of melding and testing biogeographical and paleogeographical hypotheses.