Distinctions between the Skulls of Coyotes and Dogs

1. What they did

Coyote and domestic dog bones are often found together at archaeological sites in the United States. The two are very similar in size and shape, but their relationship with people is very different, so it matters which is which. Archaeologists and museum preparators often lack clear guidance, especially for broken or incomplete skulls.

Krantz first compared the skulls of 11 coyotes from Utah with 35 domestic dogs of various breeds in 1949. He then examined several hundred more specimens from various collections, including coyotes from Montana, New Mexico and California. From these he built a checklist of traits for identifying most canine skull remains, illustrated with seven drawings.

2. What they found

General differences (best seen side by side)

• Coyotes have a longer, narrower muzzle.
• Coyote teeth tend to be longer, sharper-edged and more complex in their cusps.
• Coyote skull bones are thinner, crests sharper, and the whole skull lighter than a dog skull of similar size.
• The coyote’s lower tooth rows are nearly straight; the dog’s bend outwards more, “as though to make room for a larger tongue.”
• Coyote teeth are rarely worn down or missing and their skull sutures are rarely fused. Both are common in dogs, perhaps because dogs more often live to an older age.

Coyotes from the western states were remarkably alike. Dogs varied widely in proportions but were quite constant in the important traits.

Fourteen traits that work on a single specimen

• Frontal sinus: much smaller in the coyote, so the skull profile is an almost even curve; the dog has a pronounced bulge above the eye sockets.
• Cheekbone suture: the lower half of the suture between the zygomatic and maxillary bones is S-shaped in the coyote, nearly straight in the dog.
• Lower jaw: the back edge of the coronoid process is vertical in the coyote; in the dog it sweeps backwards at the tip.
• Sagittal crest: an adult coyote has a crest about 1 cm tall over the back third of the braincase, with the muscle lines not meeting further forward. A dog with a 1 cm rear crest has a front part at least half as tall.
• Palate: extended backwards, the coyote’s palate would miss the base of the skull; the dog’s would meet the braincase. Very short-muzzled dogs show the coyote trait.
• Auditory bullae: much larger in the coyote; the gap between them is narrower than either bulla. In the dog, the gap is wider than either bulla.
• End of the hard palate: in line with the centres of the second molars or slightly forward in the coyote; usually behind the second molars in the dog.
• Anterior palatine foramen: 3 to 4 times as long as wide in the coyote; about twice as long as wide in the dog.
• Premaxilla: in the coyote it tapers to a long narrow point about 7 or 8 mm beyond the foramina; in the dog it usually ends bluntly no more than 5 mm beyond.
• Nose opening: taller than wide in the coyote; roughly circular in the dog.
• Upper molars: the inner (medial) cusps are much more prominent in the coyote. Krantz calls this the most reliable single trait; he saw no exceptions.
• Lower first molar: the rear third has two low cusps of equal size side by side in the coyote; in the dog the inner one is only half the size of the outer.
• Lower fourth premolar: three distinct cusps plus the basal ridge in the coyote; only the larger two in the dog.
• Lower second, third and fourth premolars: seen from above, three times as long as wide in the coyote, twice as long as wide in the dog.

3. What they concluded

• Each trait has occasional exceptions, where a dog skull shows the coyote trait (rarely the reverse).
• A skull fragment should show at least two of the traits, and preferably more, for a positive identification.
• All 14 traits can be seen on a single specimen, without needing comparison skulls.

6. Other technologies, skills or innovations

• A practical identification checklist with seven labelled side-by-side drawings: side view of the skull, side view of the lower jaw, an approximate lengthwise section of the skull, the base of the skull, the upper molars, the lower first molar and the lower fourth premolar.