Supplementary Material for: Endocranial Development in the Coyote (Canis latrans) and Gray Wolf (Canis lupus): A Computed Tomographic Study

The purpose of this study was to examine the pattern of postnatal brain growth in two wild canid species: the coyote (Canis latrans) and gray wolf (Canis lupus). Adult regional and total brain volume differences were also compared between the two species as well as within each species by sex. Three-dimensional virtual endocasts of endocranial airspace were created from computed tomography scans of 52 coyote skulls (28 female, 24 male; 1 day to 13.4 years) and 46 gray wolf skulls (25 female, 21 male; 1 day to 7.9 years). Age was known in coyotes or estimated from dentition patterns in wolves. The 95% asymptotic growth of the endocranium is completed by 21 weeks in male and 17.5 weeks in female coyotes and by 27 weeks in male and 18.5 weeks in female wolves. These ages are well before age at first reproduction (coyote – 40.4 weeks; wolf – 91.25 weeks). Skull growth as measured by centroid size lags behind endocranial growth but is also completed before sexual maturity. Intra- and interspecific comparisons of brain volumes in the adult wolves and coyotes revealed that relative anterior cerebrum (AC) volume was greater in males than females in both species. Relative brain size was greater in the coyote than in the wolf as was relative cerebrum volume. However, relative AC volume and relative cerebellum and brainstem volume was greater in the wolf than coyote. One explanation for the increased AC volume in males compared to females may be related to the role of social information processing. However, additional data are needed to determine the correspondence between regional volumes and functional differences either between or within these species. Nonetheless, these findings provide important baseline data for further studies on wild canid brain variations and development.