Paleontology, Evolution and Systematics of Capybara

Abstract

A revision of evolutionary history of the capybaras (Rodentia, Hystricognathi, Cavioidea, Hydrochoeridae) is given. Caviomorph rodents arrived in South America probably during the Late Eocene from Africa by rafting. For the Early Oligocene they had already undergone the first important radiation with the differentiation of the four superfamilies in which they are classically divided. The earliest cavioids are recorded in the Late Oligocene, Deseadan South American Land-Mammal Age (SALMA) in Patagonia with the eocardiids, considered the ancestors of the families Caviidae and Hydrochoeridae. The oldest hydrochoerids, Cardiatherium chasicoense, have been recorded in the Upper Miocene (Chasicoan SALMA) of central Argentina. This species displays all the dental characters diagnostic of the family. The absence of hydrochoerids in the Middle Miocene suggests a rapid diversification of this family between 13.5 and 15.5 Ma. For the latest Miocene at least, capybaras inhabited up to northern South America, and by the Pliocene, they entered North America and the Antilles. Systematics of the fossil capybaras is mostly based on tooth morphology especially in the number and depth of re-entrant folds. Capybaras have a very peculiar cheek tooth ontogenetic development that was originally misunderstood. This fact together with a typological criterion led to a complicated systematics that included an extremely high number of 1 nominal genera and species, grouped in four subfamilies. A new criterion of cheek tooth development and evaluation of individual morphological variation led to a substantial reduction of genera and species and a new approach to the systematics of the subfamily. We group all fossil and extant capybaras in the subfamily Hydrochoerinae. Besides, we add to the Hydrochoeridae the Cardiomyinae, a group of extinct relatively large cavioids, with multilaminar last lower and upper molar that have been usually considered as caviids. By means of morphometrical (dos Reis 1994) and molecular analyses (Rowe and Honeycutt 2002) Kerodon was included within the hydrochoerids, but if it were so, its divergence should have taken place more than 10 million years ago. The fossil record suggests that capybaras developed some of their basic morphological and ethological characteristics early in their history: large size, semiaquatic habits and probably, congregation in herds.