Paleoecology of Extinct Xenarthrans and the Great American Biotic Interchange

Abstract

The Xenarthra were the most successful South American mammals to participate in the Great American Biotic Interchange (GABI) and representatives of each family dispersed to at least the middle latitudes in North America. The ability of xenarthrans to insinuate themselves into the North American fauna suggests their ecology was sufficiently different from endemic North American taxa to avoid direct competition and sufficiently different amongst themselves to avoid competition with each other. Despite the diversity of xenarthrans in South America at the time of the interchange only one member of each major xenarthran group (roughly equivalent to a family) reached temperate North America. The morphological diversity displayed by ground sloths, glyptodonts, pampatheres, armadillos and anteaters, indicates that no single ecological explanation can account for their successful dispersal into North America as each represents a distinct ecological adaptation, including a variety of feeding strategies such as omnivore/insectivore, specialized myrmecophage, and herbivory including low browser, high browser, aquatic grazer, intermediate feeder on coarse vegetation/grazer, and large grazer/intermediate feeder. Despite this ecological diversity there do seem to be some trends common to the group. Ecologically the dispersing member was more of a generalist than other members of the family and dispersing members tended to be small with a subsequent increase in size following their entry into North America.