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ABSTRACT Microvertebrate remains from a dolomitic fissure in the Middle Silurian Engadine Dolomite, Mackinac County, Michigan, represent at least 9 species of Late Holocene (Little Ice Age Interval) vertebrates. These [...]

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. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine developmental and individual variation in total endocranial volume and regional brain volumes, including the anterior cerebrum, posterior cerebrum and cerebellum/brain stem, in the spotted hyena (Crocuta crocuta). The spotted hyena is a highly gregarious animal noted for living in large, hierarchically organized groups. The social lives of male and female spotted hyenas do not differ until after puberty, when males disperse from the natal group, while females remain philopatric. Here we sought to determine whether the divergent life histories of male and female spotted hyenas are linked to differences in brain size or organization. Three-dimensional virtual endocasts were created using computed tomography from 46 spotted hyenas skulls (23 females, 22 males, 1 unknown sex) ranging in age from 1 day to 18 years. Brain volume and skull length were highly correlated (r = 0.91), and both reached asymptotic values by 34 months of age. Analyses of total endocranial volume (relative to skull length) and cerebellum/brain stem volume (relative to total endocranial volume) revealed no sex differences. However, relative anterior cerebrum volume, comprised mainly of frontal cortex, was significantly greater in adult males than adult females, and relative posterior cerebrum volume was greater in adult females than adult males. We hypothesize that the demands of neural processing underlying enhanced social cognition required for successful male transfer between matriarchical social groups at dispersal may be greater than cognitive demands on philopatric females. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Over eight kilobases (kb) of sequence from eight genes including two mitochondrial loci, Cytband 12S, and six nuclear loci,B2m,Zp3,Tcp1, Sry, SmcxandSmcy, were used to investigate phylogenetic relationships among 11 taxa representing eight species within the rodent genusMus. Particular attention was given to discerning relationships among species within the subgenusMusincluding members of a Palearctic clade (M. musculus,M. spicilegus,M. macedonicusandM. spretus) and members of an Asian clade (M. caroli,M. cookiiandM. cervicolor), as previous studies using different datasets have produced different topologies for taxa within these two groups. While parsimony analyses of the combined eight-gene dataset yielded a single, fully resolved tree, support values were lower for nodes resolving relationships within the Palearctic and Asian clades than they were elsewhere in the tree. In addition, a maximum likelihood analysis of the same eight-gene dataset yielded different topologies for both the Palearctic and the Asian clades. Both observations are indicative of clade instability. The nature of this instability was explored through a comparison with our previous study in which we included the two mitochondrial loci and only four of the six nuclear genes, and through an analysis of partitioned data, specifically mitochondrial vs. nuclear genes. This study underscores the importance of considering among-site rate variation in phylogeny reconstruction.© 2005 The Linnean Society of London,Biological Journal of the Linnean Society, 2005,84, 653–662. [ABSTRACT FROM AUTHOR]

Weaning represents a challenging transition for young mammals, one particularly difficult for species coping with extreme conditions during feeding. Spotted hyenas (Crocuta crocuta) experience such extreme conditions imposed by intense feeding competition during which the ability to consume large quantities of food quickly is highly advantageous. As adult spotted hyenas have massive skulls specialized for durophagy and can feed very rapidly, young individuals are likely at a competitive disadvantage until that specialized morphology is completely developed. Here we document developmental changes in skull size, shape, and mechanical advantage of the jaws. Sampling an ontogenetic series of Crocuta skulls from individuals ranging in age from 2 months to 18 years, we use linear measurements and geometric morphometrics to test hypotheses suggesting that size, limited mechanical advantage of the jaws, and/or limited attachment sites for jaw muscles might constrain the feeding performance of juveniles. We also examine skull development in relation to key life history events, including weaning and reproductive maturity, to inquire whether ontogeny of the feeding apparatus is slower or more protracted in this species than in carnivores not specialized for durophagy. We find that, although mechanical advantage reaches maturity in hyenas at 22 months, adult skull size is not achieved until 29 months of age, and skull shape does not reach maturity until 35 months. The latter is nearly 2 years after mean weaning age, and more than 1 year after reproductive maturity. Thus, skull development in Crocuta is indeed protracted relative to that in most other carnivores. Based on the skull features that continue to change and to provide additional muscle attachment area, protracted development may be largely due to development of the massive musculature required by durophagy. These findings may ultimately shed light on the adaptive significance of the unusual "role-reversed" pattern of female dominance over males in this species.