EVOLUTIONARY MORPHOLOGY OF THE GENUS CTENOMYS: REVIEW AND PROSPECT

VASSALLO, ALDO IVÁN

Mendoza

Simposio; International Theriological Congress; 2009

International Federation of Mammalogist

The study of digging adaptations in the subterranean rodent Ctenomys is straightforward because there is well preserved fossil record of Ctenomyidae, which allowed the characterization of early stages of adaptation. Further, species belonging to the sister family Octodontidae encompass a broad array of behavioural/structural adaptations, from surface dwelling to subterranean forms, which provides a useful comparative framework. Fossorial habits independently evolved in many mammalian lineages in association with the emergence of open environments during the Cenozoic. This is an explanation mostly based on external factors, i.e. environmental conditions. We may also ask: what internal/organism factors have triggered the emergence of this novel niche? The functional analysis of Ctenomys and its living and extinct relatives yields a remarkable result: some species within Octodontidae are capable of digging complex burrows even in the virtual absence of morphological adaptations. This notion is consistent with early ideas by Ernst Mayr, who had claimed that the shifts into novel niches are almost without exception initiated by a change in behaviour that preceded and canalised subsequent structural change. The status of some characters differing in Ctenomys species of contrasting size, such as the width of the mandible across de angle, and incisor cross-section, are the outcome of the extension of the ontogenetic trajectory, which do not differ in either slope (allometric coefficient) or intercept. This fact indicates an evolutionary ontogenetic scaling associated with skull shape variation within the limits of a genus. New data coming from in vivo estimation of biting forces might be useful to characterise more deeply one striking feature of the dual masticatory-excavatory apparatus of Ctenomys: the hypertrophy of the masseteric musculature and jaw. This information, in conjunction with previous osteological and myological analysis concerning lever arms relationships of the skull will help to understand the performance of dentoexcavation in different soil conditions.