Evolution and development of the skull morphology of canids: An investigation of morphological integration and heterochrony
This dissertation's primary objective was to test for heterochronic patterns and processes, specifically paedomorphism and neoteny within a putative ancestral-descendant pair the wolf, Canis lupus and the dog, Canis familiaris . In addition, patterns of developmental and morphological integration were investigated. Three dimensional landmark-based data were collected on an ontogenetic series of over 700 crania belonging to Canis familiaris (100 breeds) and 310 Canis lupus. Morphometric data analysis was accomplished by the following methods: cranial shape centroid and geometric mean differences, ontogenetic allometric regression, common principal component analysis (Flury, 1988), shared correlation matrix structure (SCMS), and Heterochronic Prediction and Diagnosis (Williams, 2001, Williams et al., 2003).
Heterochronic processes, including neoteny, do not describe the evolution of most dog breeds examined, although adults of a few breeds are paedomorphic, meaning they exhibit cranial morphology similar to juvenile wolves. However, there is a wide diversity of skull shapes within the globally paedomorphic breeds. Not all dog breed crania conform to the predicted cranial shape expected from a heterochronically derived descendant of Canis lupus. Some breeds' crania are indeed morphological snapshots from wolf ontogeny, having the same shape and size as a juvenile or an adult wolf. Other breeds may have a cranial shape similar to a particular stage in the wolf's ontogeny but, because of the dissociation of size and shape, their crania are not similar in size to those of the wolf at that ontogenetic stage. Still other breeds are neomorphic, i.e. similar to no stage along the wolf ontogenetic trajectory. The evolution of Afghans, Appenseller Sennenhunds, Bernese Mountain Dogs, German Shepherds, Labradors and Newfoundlands is best modeled via the heterochronic process proportioned dwarfism. Chihuahuas are the only small breed well modeled by a heterochronic process of proportioned dwarfism. St. Bernards as well as Fox Terriers, French Bulldogs, and Pugs were not well described by any heterochronic model.
During canid ontogeny, pattern and intensity of integration among cranial elements varies and adult and neonatal patterns are each unique. Ancestral patterns of developmental integration do not predict Canis familiaris integration.
Anatomy & physiology
0287: Anatomy & physiology