Evolution of morphological adaptations for digging in living and extinct Ctenomyid and Octodontid rodents (Caviomorpha: Octodontoidea).

ENRIQUE P. LESSA; ALDO. I. VASSALLO; DIEGO H. VERZI; MATÍAS S. MORA

University of Massachusetts Amherst.

Congreso; The American Society of Mammalogists: 86th Annual Meeting.; 2006

The American Society of Mammalogists (ASM).

In order to examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha) we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We surveyed morphological specializations and mapped them onto our resulting phylogenetic hypothesis. Finally, we attempted to match morphological diversity with information on the ecology and behavior of octodontoid taxa. Burrowing for sheltering and rearing is the rule within octodontids and ctenomyids. Digging adaptations developed since the Late Miocene, presumably in association with the climatic deterioration and development of open habitats characteristic of that period. However, only a few taxa evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages. Consequently, morphological changes of the forelimb associated with scratch-digging, including elongated olecranon processes, distally placed and expanded deltoid processes, and enlarged teres major processes, are not restricted to subterranean lineages. Adaptations related to chisel-tooth digging involve changes in the skull and dental characters, such as an increase in incisor procumbency and, in some cases, cross-sectional area, and expansions of the masseteric crest and angular process in the lower jaw. These features have evolved independently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Our phylogenetic approach shows that some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Adaptations for digging among ctenomyids have evolved in a mosaic fashion since the mid Miocene. In contrast, the numerous structural modifications observed in Spalacopus relative to its close relative Aconaemys are estimated to have evol.