Phylogenetic position of Abalosia and the evolution of the extant Octodontinae (Rodentia, Caviomorpha, Octodontidae)

South American octodontid rodents of the subfamily Octodontinae currently s how low species richness but great morphological and chromosomal diversity. This diversity is interpreted alternatively as the remnant of a wider past radiation or as the result of saltational evolution, These hypotheses are discussed in relation to a phylogenetic analysis of the Late Pliocene octod ontine Abalosia castellanosi. My results suggest that Abalosia, together wi th Tympanoctomys and Octomys, is part of a clade of desert specialist propa linal octodontids, which would have differentiated east of the Andes in the emergent semi-deserts of western Argentina. The presence of Abalosia in th e coastal region of central Argentina during the Upper Marplatan Age (Late Pliocene) suggests a pulse of expansion of such and environments, probably coeval with the global climatic deterioration detected around the transitio n Gauss-Matuyama magnetic ages. The phylogenetic position of A. castellanos i suggests that extinction events affected the clade of the octodontine des ert specialists. Accordingly, regardless of how rough or gradual the differ entiation of the octodontine's diversity has been, the living representativ es seem to be remnants of a wider radiation.