The Origin of the Caviomorph Rodents from a Source in Middle America

Abstract

It has long been recognized that the mammalian fauna of South America consists of three distinct parts—an ancient fraction, that reached South America in an unknown manner and from an unknown source or sources, but at least as early as the Paleocene; a modern fraction, that arrived on the continent from North and Middle America at the end of the Pliocene or the beginning of the Pleistocene, when the Panama land bridge was formed; and a third group, of intermediate age, that arrived in South America by rafting some time between the Mustersan, of probable middle Eocene age, and the Deseadan of early Oligocene age (Simpson, 1950, pp. 368–376). This last fraction includes the caviomorph rodents and the platyrrhine primates, both restricted to South America and the Antilles until Middle and South America were connected at the end of the Tertiary. Both have been postulated as having come either from Africa or from Middle America.