| Summary: | Chiari malformation is a cerebellar pathology characterized by a congenital reduction in posterior fossasize causing a downward displacement of part of the cerebellum through the foramen magnum. A recentstudy has hypothesized that this syndrome may be one resulting remnant of hybridization within the last1.7 million years between species of Homo with variable cranial capacities and morphology. In thiscontext, this study uses geometric morphometrics to analyze the morphological effect of hybridization onforamen magnum variation in a mammalian model hybrid population, specifically the eastern coyote(Canis latrans var.), a hybrid of coyotes (Canis latrans) and grey wolves (Canis lupus). Canids providean ideal model to evaluate these morphological changes as they too exhibit instances of Chiarimalformation, and have differential body sizes. A generalized Procrustes analysis was conductedfollowed by a series of principal component analyses (PCA) to delineate the shape variation associatedwith each group. Wireframe visualizations of Procrustes shape space were then analyzed to evaluate theshape of the foramen magnum in the hybrids compared to their parental taxa. Results show that thevariation of the hybrids was intermediate to the parents along both PC1 and PC2, with no significantchange observed in the shape of the foramen magnum between groups. This study concludes thatmorphological resistance to change during hybridization may cause the foramen magnum to beconstrained, which can potentially have an impact on the severity of Chiari malformation due to anundersized cranium.
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