4 Morphological Variation in the Dog

Abstract

From the diminutive Chihuahua to the giant Irish wolfhound, the diversity of canine sizes and shapes has fascinated humans for thousands of years. This chapter aims to catalog the wide array of morphological variation in the purebred dog in a qualitative manner. The physical characteristics that define a breed can be summarized into a handful of categories that allow judges, breeders, and veterinarians to recognize hundreds of different breeds. These categories are based on morphology-altering mutations that have been fixed within breeds. The diversity of morphological variation that exists in domestic dogs makes them an excellent model for understanding human morphological variation. Human congenital malformations are important medical problems that are studied in great detail, particularly craniofacial changes, limb formation, and height, all of which vary in dog breeds. Virtually any and all combinations of traits have been created and fixed within particular breeds. In addition, although not addressed in this chapter, coat patterns and colors abound in the domestic dog. These colors and patterns, combined with variation in morphology and behavior, provide the framework for the greatest diversity recognized within any single species. HISTORY OF MORPHOLOGICAL TYPES It is widely thought that dogs were domesticated from wolves. However, the location, timing, and number of domestication events remain controversial. Bones of wolves, dating from the Middle Pleistocene epoch (~500,000 years ago), have been found in association with early hominid sites (Olsen 1985). Changes in skeletal anatomy, an indication of domestication, are not evident in these remains, suggesting that humans and...