A Comparison of Animal Jaws and Bite Mark Patterns

1. What they did

Deaths from wild animal attacks are rare, and the domestic dog causes most deaths from land animal attacks in the United States. Because such cases are rare, little has been written about animal bites. The authors set out to describe the jaws and bite mark patterns of the animals most likely to bite or kill a person in North America, the Order Carnivora, to help investigators work out what kind of animal made a bite. They also suggest the information could help in cases where an animal has scavenged a body.

• Measuring skulls. They examined 486 skulls of 12 species at the Field Museum of Natural History in Chicago: five from the dog family, four from the cat family, two bears and the wolverine. Juveniles were included, because juveniles can bite.
• A new way to measure the distance between the canines. With a dial caliper, they measured three points on the upper canines: the widest point (maximum canine width), the canine tips, and the bone next to the canine (mesial bone height). On the lower jaw they measured the tips and the bone. Measuring on the bone meant skulls with missing or broken teeth could still be used. The idea is that a shallow bite registers the canine tips, while a deep bite matches the wider measurements nearer the gum line.
• Recording bite patterns. They photographed one representative skull per species (three for domestic dogs, because breeds vary so much) with a forensic scale, and pressed the upper and lower teeth into foamed polystyrene to make sample bite marks, which were also photographed.

2. What they found

Jaw shape tells the family

• Cat family: the six front teeth (incisors) sit in a very straight line.
• Dog family: the front of the jaw is very deeply curved.
• Bears and wolverines: although not related, they have very similar jaw shapes, between the cat and dog families but closer to cats. The upper front is slightly curved and the lower front very straight.
• Jaw shape alone cannot tell apart members of the same family; size is needed.

Size separates species within a family

• Cats fall into three size groups: small (domestic cat), medium (bobcat and lynx) and large (mountain lion).
• The dog family also falls into three: small (foxes), medium (coyotes) and large (wolves). Domestic dogs span all three, from toy poodles to Great Danes.
• Wolverines and bears have similar bite patterns, with some overlap in size.
• The size groups overlap: the largest domestic cats match the smallest bobcats and lynx, and the largest bobcats and lynx match the smallest mountain lions. This is partly because juveniles were included.

Distance between the upper canines (range for each species)

• Domestic cat 0.7 to 2.2 cm; bobcat 1.1 to 3.1 cm; lynx 1.3 to 3.0 cm; mountain lion 2.1 to 4.5 cm.
• Gray fox 0.9 to 2.2 cm; red fox 1.1 to 2.7 cm; domestic dog 1.3 to 4.8 cm; coyote 1.5 to 3.6 cm; gray wolf 2.3 to 5.1 cm.
• Wolverine 1.8 to 4.3 cm; black bear 2.0 to 6.4 cm; grizzly bear 3.4 to 9.6 cm.

The paper gives lower-jaw ranges too, and the full measurements for every skull.

Compared with people

Carnivores have six incisors and two very large canines in each jaw; humans have four incisors and much smaller canines. Measured canine to canine, wolf and bear arches are much deeper from front to back than a human’s. The exemplars also support an earlier observation that grizzly bear and mountain lion bite marks look similar but differ by species.

3. What they concluded

• Jaw shape helps identify the family of the animal that made a bite, and size can sometimes separate species within a family.
• Because domestic dogs vary so much in size, when an unwitnessed bite fits the dog family, domestic dogs should be considered alongside wild canines.
• The polystyrene exemplars and photographs are still pictures of a dynamic action; real animal bites can be very violent, with deep gouges, tearing and loss of tissue, and need great skill to analyse.
• This is an initial study; more data and analysis are needed to understand this complex subject.

6. Other technologies, skills or innovations

• A modified way of measuring intercanine width at three points on the canine (widest point, tip and adjacent bone), to allow for bites of different depths.
• Foamed polystyrene bite exemplars, photographed with an American Board of Forensic Odontology (ABFO) No. 2 scale so they could be shown life size and compared in Adobe Photoshop.
• Mitutoyo dial caliper; Nikon CoolPix 5700 camera on a copy stand.