RYBCZYNSKI, Natalia; Canadian Museum of Nature, Ottawa: Behavioral evolution in fossil castorids (beavers)

Castorids present an unusual opportunity to study behavioral evolution because their robust fossil record includes numerous behavioral artifacts. For some castorids the behavioral evidence indicates a close correspondence between behavioral and morphological specialization, but in other cases the behavioral trait appear unassociated with any morphological traits. Thus castorids may represent an excellent case study for examining the evolutionary relationships between morphology and behavior. Toward this end I have begun by examining patterns of behavioral evolution in a phylogenetic context. Within castorids two types of behavioral specialists were recognized, tooth-diggers and wood-cutters. These behavioral specialists were identified using morphological (quantitative comparative) and/or behavioral evidence. I conducted a series of cladistic analyses (36 taxa, 89 morphological characters) that varied in the exclusion and inclusion of various taxa and character weighting regimes. Mapping characters onto all the most parsimonious cladograms yielded similar patterns of behavioral evolution. The results suggest that fossoriality arose primitively within castorids, whereas tooth-digging, a fossorial specialization, arose at least twice. Assuming parsimony, wood-cutting appears to have evolved only once from a morphologically �unspecialized�, common ancestor that lived at least 20 million years ago. At least six genera descended from this ancestor, suggesting that the acquisition of wood-cutting behavior may have been associated with an adaptive radiation. Supported by NSF DIG grant IBN-0073119.