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Testing hypotheses of the evolution of encephalization in the Canidae (Carnivora, Mammalia)

¹ John A. Finarelli. Committee on Evolutionary Biology, University of Chicago, 1025 East Fifty-seventh Street, Chicago, Illinois 60637
² Present address: Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, 1100 North University Avenue, Ann Arbor, Michigan 48109. john.finarelli{at}umich.edu

Evolutionary trends observed over large clades have the potential to mask underlying trends that occur within their constituent subclades. A recent study of encephalization in the Caniformia (Carnivora, Mammalia) found evidence for an abrupt increase in median log-encephalization quotients (logEQs), indicating higher brain volume relative to body mass, at the end-Miocene, but gradual increase in the variance of logEQs. In this study, new endocranial volume estimates for fossil taxa in the well-sampled caniform subclade Canidae are reported. Using the encephalization data for the Canidae, hypotheses of evolution in encephalization allometries were tested with respect to canid phylogeny. The Akaike Information Criterion and likelihood ratios recovered support for a preferred hypothesis of the evolution of canid encephalization, which proposed two distinct allometric relationships: (1) a plesiomorphic grade of encephalization in the subfamilies Hesperocyoninae and Borophaginae and the paraphyletic canine genus Leptocyon, and (2) an apomorphic grade in the crown radiation of Caninae. This defines a shift in to higher encephalization, but without an associated change in the variance around the allometry. Increased canid encephalization coincides with a reorganization of the brain and the observed trend may reflect the evolution of complex social behavior in this clade.