Size, shape and development in the evolution of the domestic dog

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An explanation for the ubiquitous morphological changes during the evolutionary divergence of the domestic dog (Canis familiaris) from the wolf (Canis lupus) has proven elusive. These changes include size reduction, facial shortening and tooth crowding. The ubiquity of these changes suggests that they are unlikely to be direct products of human selection. In this paper explanation of morphological change is approached through allometric analysis of craniometric data from prehistoric domestic dogs from North America and northern Europe and from recent wild Canis. Results indicate that anterior cranial length dimensions are tightly scaled among all Canis, while the dogs show divergent allometries on cranial width dimensions. These patterns are consistent with previous allometric studies involving modern dog breeds. Morphological patterning in dogs is not reasonably explained solely as a by-product of biomechanical constraints associated with size reduction. Rather, morphology is constrained by developmental boundaries, reflecting heterochronic alterations produced by strong selection for size reduction and modified reproductive strategy. Unique dental allometries of dogs stem from lack of tight developmental integration between dental growth and overall somatic growth. Further analysis should focus on the relationship between ancestral ontogeny and adult morphology in dogs.