AN APPRAISAL OF THE VICARIANCE HYPOTHESIS OF CARIBBEAN BIOGEOGRAPHY AND ITS APPLICATION TO WEST INDIAN TERRESTRIAL VERTEBRATES

Pregill, G. K. (Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560) 1981. An appraisal of the vicariance hypothesis of Caribbeain biogeography and its application to West Indian terrestrial vertebrates. Syst. Zool., 30:147-155.-Antillean land vertebrates came from North and South America sometime in the past, but the question of when and by what means continues to segregate zoogeographers. The recently advocated vicariance hypothesis of Caribbean biogeography assumes a "proto-Antillean" archipelago that contained the antecedents of the modern West Indian biota. This hypothesis, however, is contradicted by current knowledge of Caribbean tectonics, the composition of the fauna itself, and the fossil record of North and South America. The evidence is more accurately interpreted as indicating that the Antilles are oceanic in origin, and modern terrestrial vertebrates probably began arriving by overwater dispersal during the Oligocene and continued to do so through the Quaternary. [Caribbean; vicariance; dispersal; tectonics; Greater Antilles; vertebrates; fossil record.] The origin of the West Indian terrestrial vertebrate fauna is one of the more conjectural issues in biogeography, mostly because of the virtual absence of Tertiary fossils there, and the fact that many systematic questions remain unanswered about modern genera and species. Most of the hypotheses invoked to explain vertebrate biogeography were proposed prior to the publication of plate tectonic theories of the Caribbean basin during the last decade. Earlier in this century, the debate between proponents of a land-bridge connection versus those favoring over-water dispersal was quite intense. Indeed, in his later review of West Indian land mammals, Simpson (1956:7) was obliged to state that, "When I first drafted the present paper it seemed useless to reopen a question that had been so thoroughly discussed and had, I felt, been settled." Simpson affirmed Mathew's assessment that certainly for land mammals, over-water dispersal was more consistent with the evidence. Then as now, the origin of the Antillean vertebrate fauna remains a subject of interest. After the initial burst of data on Caribbean tectonics in the early 1970's, the origin of West Indian vertebrates was reexamined by Rosen (1975) using the principles of vicariance biogeography (Croizat et al., 1974). Recently, MacFadden (1980) applied the same approach in attempting to explain the origin of West Indian insectivores (Mammalia). Rosen's ideas provoked considerable discussion about the philosophical aspects of the method, which were argued at length in the pages of Systematic Zoology. The critical discussions pertaining to the islands and animals themselves have been conducted mainly through informal conversations, seminars and annual meetings; there has been little follow-up in print (see Lillegraven et al., 1979:297). The purpose of this essay is to review the existing evidence bearing on the origin of West Indian land vertebrates, and to show how this evidence may be interpreted other than by the vicariance hypothesis, my specific criticsm being that the "proto-Antillean" archipelago envisioned by the model's proponents has little basis in fact. The scope of this paper is limited by its restriction of examples to land vertebrates, and amphibians and reptiles in particular, but the conclusions