Postcranial morphology of the extinct caviine rodent Microcavia criolloensis (late Pleistocene, South America)

A comparative study of the appendicular skeletal morphology, with a particular emphasis on the autopodial elements (manus and pes), of the extinct caviine rodent Microcavia criolloensis (Late Pleistocene, Uruguay), together with that of living species of Microcavia and some allied caviines is performed. Burrow-digging and above-ground behaviour by M. criolloensis could have evolved in the Late Pleistocene, as with its relative M. australis in the Recent. This is suggested based on the morphology of preserved articulated skeletons along with fossil burrow-like structures. The most remarkable features are: in its forelimb, where the humerus has a structure that would have allowed it to perform similar activities to M. australis, based on humeral width across the epicondiles relative to total humerus length index and a good resistance as indicated by high values relating the diameter of the diaphysis to its total length. Qualitative comparison shows that M. criolloensis had a stout, wide manus with relatively short digits including short, wide phalanges, despite its large size. In its hind limb there is a stout hind-foot with relatively short and wide metatarsals and phalanges, as compared with those of the recent species, that could arguably be considered a useful tool for shovelling out displaced soil. The generalized morphology suggests above-ground behaviour together with digging ability. The environmental adaptations of M. criolloensis are also briefly discussed, which seem to differ from those of its extant relatives. (C) 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 795-806.