Evolution of Appendicular Specializations for Fossoriality in Euryzygomatomyine Spiny Rats across Different Brazilian Biomes (Echimyidae, Hystricognathi, Rodentia)

The evolution of subterranean and fossorial rodents has been linked to the Neogene climatic shift to xeric conditions leading to open vegetation, like prairies and grasslands; most modern subterranean rodents occur in arid and open areas. Among South American spiny rats (family Echimyidae), the subfamily Euryzygomatomyinae includes both fossorial (Clyomys and Euryzygomatomys) and ambulatorial (Trinomys) genera, some of them endemic to open vegetated areas and other ones restricted to forested regions. The closely related genus Carterodon is also a fossorial rodent endemic to open vegetated areas. If the open environments constitute a determinant factor triggering the evolution of fossoriality in these spiny rats, it is expected that the fossorial lineages evolving since the Miocene in open environments (Carterodon sulcidens and Clyomys laticeps) show morphologies more specialized for digging than those currently restricted to Atlantic Forest habitats (Euryzygomatomys spinosus). Moreover, it is likely that Trinomys species specialized for xeric environments (T. albispinus and T. yonenagae) show incipient adaptations for fossoriality. The appendicular skeleton of three fossorial and five ambulatorial echimyid species were morphometrically analyzed with multivariate statistical approaches in order to test these presuppositions. The analyses showed that the appendicular morphology of T. yonenagae and T. albispinus, in comparison with the Atlantic Forest Trinomys species, and of C. sulcidens and C. laticeps in relation to E. spinosus are more adapted to scratch-digging activities, corroborating the hypothesis that open environments favor the evolution of fossoriality in spiny rats.