Ecomorphological diversification among South American spiny rats (Rodentia; Echimyidae): a phylogenetic and chronological approach.

The phylogeny of South American spiny rats (Rodentia; Echimyidae) was studied using the exon 28 of the von Willebrand Factor nuclear gene (vWF). Sequences were analysed separately and in combination with a mitochondrial dataset (cyt b, 12S and 16S rRNAs) used in previous publications. The basal polytomy of echimyids was partially resolved and unexpected intergeneric clades were recovered. Thus, the intimate nested position of Myocastor within echimyids is evidenced. A well-supported clade is identified, including all the arboreal genera, and a group formed by Myocastor, Thrichomys, and Proechimys+Hoplomys. The clustering of Euryzygomatomys+Clyomys with Trinomys is also suggested. On the opposite, the phylogenetic position of Capromys as well as the relationships among arboreal genera remain unclear. Molecular divergence times were estimated using a Bayesian relaxed molecular clock and suggest a Middle Miocene origin for most of modern genera. The ecomorphological diversification of echimyids is discussed in the light of these new results and past environmental modifications in South America.