Forelimb proportions and fossorial adaptations in the scratch-digging rodent Ctenomys (Caviomorpha)

ELISSAMBURU ANDREA; DE SANTIS LUCIANO

La Plata

Jornada; XXIV Jornadas Argentinas de Mastozoología, SAREM; 2011

SAREM

Ctenomys (tuco-tuco; Rodentia, Caviomorpha) is a South American rodent genus of the family Octodontidae (sf. Ctenomyidae). Ctenomys is considered a “scratch-digger”. We compared the forelimbs of Ctenomys azarae to species of caviomorph rodents to identify morpho-functional variation in osseous elements related to fossorial habits. Eighty-eight adult specimens of caviomorph rodents belonging to 13 extant species were studied. Eight measurements of the humerus and ulna were used to construct five functional indices that were subjected to principal components analysis and simple comparisons among means. Ctenomys has a general morphology similar to that of terrestrial caviomorph rodents, but exhibits some features that reflect its specialized fossorial condition. Ctenomys has large epicondyles, even compared to other digging forms. These features indicate greater muscular development and capacity for force production in the pronators and supinators of the forelimb and hand, and flexors of the hand. Another exceptional characteristic of Ctenomys is the development of its deltoid complex, indicating a large moment arm for the deltoid and latissimus dorsi muscles, which increases the capacity for force production on humeral flexion. Humeral indices are the best variables for differentiating fossorial forms from diggers, occasional-diggers, generalized, and cursorial forms. Fossorial forms differ principally in functional specializations of the humerus and the hand for digging. Limb segments may be used differently by highly fossorial, scratch-digging forms.