The Great American Biotic Interchange in Florida

Abstract

Late Neogene vertebrate faunas from Florida provide the most complete record of South American mammals and birds that arrived in temperate North America during the Great American Biotic Interchange (GABI). The first major pulse of the GABI began in the early Hemphillian (late Miocene, ~9 Ma), defined in part on the first appearance of two sloths of South American origin, the megalonychid Pliometanastes and the mylodontid Thinobadistes. The type localities of Pliometanastes protistus (McGehee Farm) and Thinobadistes segnis (Mixson’s Bone Bed) are both earliest Hemphillian (8-9 Ma) sites from northern Florida. Pliometanastes evidently gave rise to Megalonyx in the late Hemphillian. The latest Hemphillian (~5 Ma) Palmetto Fauna documents the earliest occurrence of Megalonyx in Florida. The second major pulse of the GABI occurred during the late Pliocene and early Pleistocene, from 2.7 to1.5 Ma. The late Blancan is defined by the first appearance in temperate North America of a diverse assemblage of vertebrates from South America, including ten genera, all of which occur in Florida during the late Blancan: the giant flightless bird Titanis, the glyptodont Glyptotherium, the armadillos Dasypus and Pachyarmatherium, the pampathere Holmesina, the mylodontid Glossotherium, the megatheriid Eremotherium, the porcupine Erethizon, and the capybaras Hydrochaeris and Neochoerus. During the late Blancan, Titanis, Dasypus, Pachyarmatherium, Holmesina, Eremotherium, and Hydrochaeris are primarily restricted to Florida, whereas Glyptotherium, Glossotherium, Erethizon, and Neochoerus are more widespread, occurring in Florida as well as the western United States. These ten genera have their earliest occurrence in early late Blancan (2.2-2.7 Ma) sites from Florida and/or the southwestern United States. Four genera of South American mammals arrived in temperate North America somewhat later: Paramylodon and Desmodus in the latest Blancan (1.8-2.2 Ma), Nothrotheriops in the early Irvingtonian (1.6-1.8 Ma), and Didelphis in the medial Irvingtonian (~0.8 Ma).