The crania of Canis latrans (coyote) and Canis familiaris (dog) are morphologically similar and can be confusing when trying to differentiate between the two. Dogs and coyotes have similar origins that go back into the Oligocene. The hespaeocyon is the extinct creature that gave rise to all canids (Colbert 1958:68). Hence, many canid skulls look very similar in structure. There is a definite distinction between dogs and other canids. In compared patterns of intracranial allometry and morphological diversity between domestic dog and wild canid species, domestic dogs were shown to be morphologically distinct from all others except wolf like canids (Wayne 1985:247). Dogs having a similarity to wolflike canids can be explained by the theory that dogs are descended from wolves. Some of the morphological changes that occurred in the domestication are size reduction, shortening of facial region, and paedomorphism (retention of juvenile characteristics) (Morey 1992:182). Coyotes evolved separately from wolves and dogs. Coyotes are more related to foxes than wolves and a have a more generalized biology than the other canid counterparts. They have narrower skulls than wolves and the jaws have not developed as wide as the wolves, which, in the case of dogs compromises gripping power (Nowak 1978:5). In his paper "Distinction between the skulls of coyotes and dogs," Krantz (1959) gives an excellent description of gross morphological differences between dogs and coyotes. The Coyote has the following characteristics -- A longer narrower muzzle, small frontal sinus, s-shaped zygo-maxillary suture, a vertical posterior border of coronoid process, a plane of palate that would miss skull if extended, the space between the auditory bulla is narrower than either bulla, internal nares are in line or slightly forward of second molars, the anterior palatine foramen is three or four times long as it is wide, the lower first molar rear cusp is the same size as the other two, the second, third, and fourth premolars are three times long as they are wide, and the coyote has a straight tooth row. The dog has a shorter wider snout, tooth row that bends outward, often has teeth missing, pronounced bulge over occipital orbits, straight zygo-maxillary suture, the posterior coronoid process extends backwards at the tip, the plane ofthe palate would hit the skull, the space between the auditory bulla are wider than the bulla, internal nare usually extend to a point behind second molars, anterior palatine foramen two times as long as it is wide, lower first molar rear cusps differ in size, and the second, third, and fourth premolars are three times long as they are wide. Craniometric differences exist as well. If the molar tooth row is 3.1 or more times that of a palatal width, the specimen is a coyote. If the molar tooth row is 2.7 times or less, the specimen is a dog. (Howard 1949:170) Despite all these differences confusion may still arise when differentiating between the two species, especially if the cranium is incomplete, or if the characteristics look like they could belong to dog or coyote. More craniometric evaluations may be utilized to establish mathematical guidelines for distinguishing the two species and the evolutionary processes. Additional indexes would be helpful in defining the correct species and establishing evolutionary relationships.