Contrasting Phylogenetic and Diversity Patterns in Octodontoid Rodents and a New Definition of the Family Abrocomidae

Abstract

Octodontoidea is the most species-rich clade<br />among hystricomorph rodents. Based on a combined parsimony<br />analysis of morphological and molecular data of extinct<br />and extant species, we analyze the history of South<br />American octodontoids and propose ages of divergence older<br />than interpreted so far. Early Abrocomidae are recognized for<br />the first time, and a new definition of the family is provided.<br />Traditionally accepted fossil-based times of origin for the<br />southern clades are reinterpreted as later stages of differentiation<br />markedly uncoupled from the origin, differentiation implying<br />specializations for open environments as shown in a<br />morphospace of skull variation. Origin of crown groups is also<br />strongly uncoupled from origin of clades as a consequence of<br />extinction of deep lineages. In the resulting diversity pattern of<br />modern southern clades of octodontoids, the combination of<br />greater disparity, less content of evolutionary history, and lower<br />taxonomic diversity, compared to their northern counterparts,<br />appears at first counterintuitive.We propose that primary<br />components of diversity derived from evolutionary transformation<br />or anagenesis, on the one hand, and from cladogenesis<br />and extinction, on the other, should not be considered<br />associated, or at least not necessarily. Certain patterns of<br />relationships between these distinct components could be<br />driven by environmental dynamics. Like environments,<br />octodontoid diversity would have been more stable in northern<br />South America, whereas in the south, both strong adaptive<br />change and extinction would have been triggered by emerging<br />derived environments.