Domestic dogs (Canis lupus familiaris) exhibit a wide range of cranial morphologies. This diversity in skull shape is largely the result of modern selective breeding practices. This project investigates the impact of selection for facial reduction on canine neuroanatomy. Previous research has indicated that the breeding for reduced faces in dogs has led to global impacts in the shape of their skull and mandible. This previous research has largely failed to consider, however, the impact of these breeding practices on the soft neuroanatomical tissue. We generated endocasts from an existing set of clinically‐obtained CT scans. This sample consists of a variety of dogs with various cranial morphologies representing four known breeds as well as a comparative sample of dogs of unknown breed. We recorded three‐dimensional coordinate data for 31 landmarks representing various gyri, sulci, and other neuroanatomical landmarks. Placing landmarks at these locations allowed us to analyze differences in shape of the endocasts. Using geometric morphometric analysis, we found that the endocast shape variance in this sample is correlated with cephalic index and as a result, it is clear that selection for facial reduction has caused a perceivable effect on canine neuroanatomy. Furthermore, we found that the majority of the shape variance in the sample was associated with olfactory anatomy. Despite this fact, when the olfactory anatomy‐associated landmarks were excluded from the sample, the rest of the brain morphology was also correlated with cephalic index. The results of this project indicate that modern breeding practices, specifically the selection for dogs with squished faces, have significantly impacted canine neuroanatomy.

The range of cranial morphology seen in domestic dogs (Canis lupus familiaris) is a direct result of thousands of years of selective breeding. This article is the first to investigate how selection for reduced faces in brachycephalic dogs impacted the neuroanatomy of the canine brain through the analysis of endocasts. Previous research has demonstrated global effects on the shape of the bony cranium as the result of these breeding practices; however, these studies have largely focused on the bony structures of the skull and failed to consider the influence of facial reduction on the soft tissues of the brain. We generated endocasts from an existing set of clinically‐obtained CT scans representing a variety of dogs with various cranial morphologies. These dogs represented four breeds as well as a comparative sample of dogs of unknown breed. We recorded three‐dimensional coordinate data for 31 landmarks representing various gyri, sulci, and other neuroanatomical landmarks that allowed us to analyze differences in shape of the endocasts. Through geometric morphometric analyses, we determined that the endocast shape variance in this sample is correlated with cephalic index, and thus the selection for facial reduction has caused a perceivable effect on canine neuroanatomy. Additionally, we found the majority of the shape variance in the sample to be associated with olfactory anatomy; however, the rest of the morphology also correlates with cephalic index. The results of this article indicate that modern breeding practices and the selection for dogs with short faces have significantly influenced canine neuroanatomy.

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Postorbital septation is a character that unites haplorhine primates. As a result, evidence of postorbital septation is expected for fossil primates that may be ancestral to both modern tarsiers and modern anthropoids. Our previous work on newborn primates has indicated that postorbital septation in tarsiers is secondary to growth of their large eyes. If this is the case, postorbital septation is convergent in tarsiers and anthropoids, and therefore should not be expected in their fossil ancestors. Here, we used morphometric analysis of the cranium and endocast of newborn and adult primates to show that postorbital septation in the order Primates may be explained by shape of the brain. We used a sample of over thirty species of modern primates representing all major clades, with individuals representing both newborn and adult stages. The newborn stage is most informative for understanding spatial relationships of soft tissues during formation of the skull. MicroCT image data were used to create virtual reconstructions of the cranium and endocast as an estimate of brain shape. Fixed landmarks were used to capture the shape of the cranium, and sliding semilandmarks represented the contour of frontal and temporal lobes on the endocast. As expected, morphometric analysis showed a significant effect of phylogeny on cranial and endocast shape in both newborns and adults. Notably, the phylogenetic effect was apparent in only the contours of the frontal and temporal lobes, independent of cranial shape. We present 3D models of the endocast and cranium of newborn primates to illustrate the spatial relationship of brain and facial structures as a mechanism for postorbital septation in anthropoid primates.