Evolution and systematics

The family Caviidae first appears in the fossil record during the middle Miocene of South America. The family is a member of the monophyletic Cavioidea, a superfamily containing three additional families, Agoutidae, Dasyproctidae, and Hydrochaeridae. Traditionally, the Caviidae has been subdivided into two subfamilies, with Galea, Cavia, Microcavia, and Kerodon placed in the subfamily Caviinae and Dolichotis and Pediolagus in the subfamily Dolichotinae. Based on morphological studies, capybaras of the family Hydrochaeridae are considered to be the closest relative to the Caviidae. A molecular phylogenetic study by Rowe and Honeycutt in 2002 suggests considerable modification of the current phyloge-netic arrangements of both genera in the Caviidae and relationships among families in the superfamily Cavioidea. Cavids appear most closely related to the family Agoutidae, and rather than being a separate family, these molecular data suggest that the Hydrochaeridae is related to Kerodon, and these two lineages are most closely aligned with Dolichotis and Pe-diolagus, members of the subfamily Dolichotinae. Therefore, the Caviinae is confined to three genera, Cavia, Microcavia, and Galea, with the first two genera being more closely related. Assuming that Kerodon was a member of the Caviinae,

Lacher in 1981 suggested that similarities in the social system seen in Kerodon and members of the Dolichotinae provided evidence of convergence in response to similar habitat constraints and the distribution of resources. The molecular phylogenetic arrangement has implications for understanding the evolution of life history traits, especially those related to mating systems and resource availability. The placement of the rock cavy, Kerodon and Hydrochaeris, as members of the Dolichotinae suggests that shared ancestry, rather than similarities in ecological constraints, best explains the evolution of social behavior in these rodents. In this regard, both the rock cavy and the capybara have a harem-based polygynous breeding system and are habitat specialists. If the molecular data are correct, then the ancestor to capybaras, rock cavies, maras, and salt-desert cavies may have been highly social. This complex social system may very well be associated with patchily distributed resources.

The genus Cavia is the most diverse in terms of species and overall geographic distribution. Although as many as eight species have been recognized, Wilson and Reeder in 1993 listed five species. The other Caviinae genera, Micro-cavia and Galea, each contain three species, whereas Kerodon

A rock cavy (Kerodon rupestris) resting its front paws on a branch. (Photo by © Frank W. Lane; Frank Lane Picture Agency/Corbis. Reproduced by permission.)

is represented by one species with a restricted distribution. Although Pediolagus salinicola was considered a species within the genus Dolichotis, recent treatments based on morphology and nucleotide sequences suggest that it represents a genus separate from the currently recognized Dolichotis patagonum.

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