Endocranial Development in the Coyote (<b><i>Canis latrans</i></b>) and Gray Wolf (<b><i>Canis lupus</i></b>): A Computed Tomographic Study

Abstract

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.

Global elongation and high shape flexibility as an evolutionary hypothesis of accommodating mammalian brains into skulls

“…Such partitions are only approximate representations of brain regions because they do not allow for internal brain boundaries. However, this method has been successfully used as a general indicator of overall brain proportions (Bertrand et al 2019a;Sakai et al 2016;Sakai et al 2018) and is used with this caveat here. A log-shape ratio approach was used to standardize the partition volumes with respect to scale (Mosimann 1970).…”

Digital Endocasting in Comparative Canine Brain Morphology

“…Computed tomography (CT), which is a significant exploratory tool in biology ( 9 , 10 ), is one of the most useful techniques for digitizing bone structures and making endocranial models from them ( 11 ). The resulting digital endocasts reflect the morphology of the brain ( 12 – 16 ) and the associated structures, such as the vascular system ( 17 ) and the cranial nerves ( 18 ). Mammals and birds are generally considered to be highly encephalized taxa ( 19 – 21 ), and, as their brains fill their cranial cavities, there is a strong correlation between the volume and the morphology of the endocasts and the brains in these species ( 20 ).…”

Ontogenetic origins of cranial convergence between the extinct marsupial thylacine and placental gray wolf

“…The thylacine and wolf exhibit lineage-specific developmental patterns, exhibiting distinct heterochrony in their cranial ontogeny. Wolves are born after a gestation of~65 days in a relatively altricial state but possess a largely ossified skull 50,51 (mean skull length 54.3 mm; n = 4, Supplementary data 1), with closure of all major cranial sutures except between the parietal and occipital, which remains partially open. At birth the wolf is substantially larger and more developed than the hyper-altricial thylacine, which by 1.5 weeks after its~21-35 day gestation 52 had a total skull length of 12 mm (n = 1, Supplementary data 1) and retained open sutures between all major cranial bones 49 .…”

“…Sampling. Three-dimensional digital cranial models for seven species of mammals, including the thylacine and gray wolf, were acquired from published studies 7,[49][50][51]62,68 , public repositories (Digimorph, MorphoSource, Digital Morphology Museum), or newly generated using X-ray CT on museum specimens (Supplementary data 1). Five marsupial species were chosen for comparison with the thylacine, subject to their availability.…”