1Department of Anthropology, University of Massachusetts, Amherst, 2School of Biomedical Sciences, The University of Queensland, Australia, 3Department of Earth Sciences, University of Hong Kong, China, 4Zoology, Field Museum of Natural History, Chicago, 5Department of Evolutionary Biology, Technical University of Braunschweig, Germany, 6School of Biological Sciences, The University of Queensland, Australia, 7Department of Anatomical Sciences, Stony Brook University
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Because there is virtually no Malagasy vertebrate fossil record between the Late Cretaceous and the Late Pleistocene, and because all but one of the vertebrate groups discovered in the island’s rich Mesozoic deposits have left no descendants, the colonization history of Madagascar’s vertebrates is knowable only indirectly. The number of vertebrate clades present on Madagascar during the Quaternary (excluding those that were introduced, deliberately or inadvertently, by humans) would have depended on (1) vertebrate clade survival across the K/T boundary, (2) rates of colonization during the Cenozoic, and (3) rates of clade extinction. Some vertebrate clades must have existed for which we have no fossil record, but their number can be estimated using models of island biogeographic turnover and equilibrium. Such models may be crude, but for any conclusion that depends on them, we can estimate reasonable boundary conditions. Analyses of phylogenetic topology, especially when coupled with estimates of divergence timing, allow us to reconstruct the timing and area(s) of origin for many known Late Pleistocene/Holocene vertebrate groups. Using these analytical tools, and considering 81 Late Pleistocene/Holocene clades most of which descended from Cenozoic colonizers, we infer significant changes in the temporal patterns of colonization of different groups of Malagasy vertebrates, and we interpret them in the context of key geological, geophysical and oceanographic information. Most notably, the rate of arrival of terrestrial (rafting) vertebrates declined dramatically after the mid-Miocene, when ocean currents became less conducive to their arrival from Africa.