Tropical and western influences in vertebrate faunas from the Pliocene and Pleistocene of Florida

Abstract

Extralimital and extinct species of birds and mammals with either tropical or western affinities are characteristic of numerous Florida Pliocene and Pleistocene vertebrate faunas. These sites document nonanalog or disharmonious faunas, recording the association of certain genera or species that are no longer sympatric, in particular taxa now restricted to drier habitats in western North America or tropical habitats in Middle America occurring together with species still found in Florida and the southeastern United States. Extralimital or extinct taxa of western origin in Florida Plio-Pleistocene nonanalog faunas include: the mammals Antrozous, Lepus, Spermophilus, Thomomys, and Baiomys; and the birds Gymnogyps californianus, Teratornis merriami, Aquila chrysaetos, Tympanuchus cupido, two species of Glaucidium, and Pica pica. A large influx of tropical species occurred in Florida late Blancan and early Irvingtonian sites, primarily consisting of taxa of South American origin involved in the Great American Biotic Interchange. Besides large Interchange mammals, other mammals with tropical affinities now extinct or extralimital to Florida include: the bats Desmodus archaeodaptes, Desmodus stocki, Mormoops megalophylla, Pteronotus pristinus, and Eumops underwoodi, the carnivores Leopardus pardalis, Leopardus wiedii, Panthera onca, two species of Conepatus, and Tremarctos floridanus, and the peccary Pecari. Tropical birds in Florida Plio-Pleistocene faunas include the extralimital Tachybaptus dominicus, Laterallus exilis, Jacana spinosa, Buteogallus urubitinga, Milvago chimachima, Vanellus chilensis, and Ceryle torquata; as well as several extinct species including Titanis walleri, a chachalaca (Family Cracidae), Amplibuteo concordatus, Spizaetus grinnelli, and Cremaster tytthus. These tropical and western taxa indicate the presence of biogeographic corridors during Plio-Pleistocene glacial intervals that connected the Florida peninsula to both the arid western United States and tropical Middle America. A mosaic of desert grassland and savanna habitats intermixed with wetlands apparently extended eastward from the arid Southwest through Texas and along a southeastern corridor to the Florida peninsula. A Gulf Coast savanna corridor supporting savanna and thorn scrub habitats probably existed during glacial low sea level stands on the exposed continental shelf and coastal plain along the northern margin of the Gulf of Mexico, connecting the Florida peninsula with Mexico and Central America. The occurrence of both tropical and western taxa in some of the same faunas strongly indicates that these distributional patterns were contemporaneous and corresponded to climatic conditions and vegetational associations that no longer exist in Florida.