Curiosity about Bones


Ever been curious about what type of animal a particular skull belongs to? A person can study a skull and its features to learn about the animal’s behavior, diet, habitat, and relation to other animals. Studying a skull to determine different things about the animal involves using one’s eyes, hands, and brain.

In the process of inferring information about an animal from the animal’s skull, one can understand the relationship between the skeletal structure and the animal’s environment. An animal’s environment influences how the animal develops based on the adaptations and structures that the animal requires to survive. Animals develop into three environmental categories of lifestyle: carnivore, herbivore, and omnivore. Two indicators of each of these lifestyles are the shape and arrangement of the teeth, and the structures of the jaw.

Animals have two jaws: the mandible (the movable, lower part of the jaw that is attached to the rest of the skull with muscles that help with chewing and strengthening of the jaw), and the maxilla (the upper, immovable part of the jaw that is fused to the main portion of the skull). The jaws provide stability and leverage for the teeth to hold, tear, and grind food. Jaw shape is a good indicator of the type of environmental lifestyle that an animal exhibits.

The jaws of a carnivore are designed to eat insects and animal flesh. Carnivores are adapted to catch prey using their speed, strength, and special appendages like claws used for hunting and killing. Carnivorous jaws have a curved mandible so that there is more strength at the front of the jaw for the incisors (front teeth) and canines to hold prey and tear flesh.

Try the “roll test” to determine if the skull is carnivorous: rest the skull on the mandible, on a flat surface. Place your hand flatly on the dome of the cranium and push the skull forward and backward in the plane of the nose. If the skull roles, it is most likely carnivorous. If it does not roll easily then it is the skull of an omnivore or an herbivore.

Carnivorous teeth are also specially adapted for chewing animal products. Carnivorous teeth have sharp points and serrated edges used for tearing and cutting flesh, because animal tissue is softer than plant tissue and tears more easily. The incisors are sharp and effective at cutting and piercing.


Animals that lack pointy teeth and curved jaws are built for eating other types of foods: plant material. These roughage-seeking animals are called herbivores, and they subsist mostly on plants. One of the herbivore’s major physical characteristics is the design of their teeth. Herbivores have flat molars and a typical absence of canine teeth and bicuspids. Three groups compose the category of herbivore, all of which possess special adaptations. The groups are rodents, ruminants, and perissodactyls.





Rodents, such as chipmunks, rats, and mice, wear a single pair of long, flat incisors in the mandible and maxilla.

Ruminants, such as cows and moose, have incisors on the mandible but not the maxilla. Their molars are flat and slant inward with ridges on the grinding surfaces. The final group belongs to the perissodactyls, which include animals like horses. These animals boast wide, sharp-edged incisors on the mandible and maxilla, unlike the ruminants and rodents. Flat and ridged molars slant inward for better use of grinding plant material.


All of the herbivores have flat-bottomed jaws. The mandible tapers from wide near the ears, to narrow at the nose. This arrangement allows for more strength to be exerted on the rear portions of the jaw, where herbivores are grinding plants. Some herbivores’ jaws, like those of the rodents, do not follow this model. Rodents’ mandibles are curved, which allows for increased strength in the incisors and molars, as rodents need to gnaw hard foods and then grind them.

The herbivores and carnivores compose the extremes of the animal kingdom with respect to environmental lifestyle categories. The animal group that resides in the middle belongs to the omnivores. Omnivores are a variable, blended group. They are designed to eat any kind of food depending on what is available: vegetation, animals, or left over meat from a recent kill. Omnivores can adapt their diet easily depending on the food that is available, which lends them a versatile skull. Tooth characteristics are a good indicator of an omnivorous animal because these animals share a lot of common skull features with their herbivorous and carnivorous counterparts, as they eat components of both types of diet. Omnivores have a well developed set of teeth: incisors, canines, bicuspids, and molars, on the mandible and maxilla.



Omnivore jaws also share characteristics of herbivorous and carnivorous mandibles. There are three shapes that omnivorous mandibles occupy: short and flat (for example, humans), long and flat or slightly curved (for examples, bears and pigs), and long and curved (for example, dogs and opossums).



The animal’s jaw structure and tooth arrangement can be used to distinguish animals in each environmental lifestyle category, and further research can be conducted about the specific diet and behaviors that the animal exhibits. For further information about an animal and its classification, one can also study other skull structures, like the nasal cavity, the orbits or eye sockets, and the cranium, which is the dome portion of the skull that protects and secures the brain.

Animals are innovative, independent, unique, and widespread. Have fun appreciating their features and learning about relationships between animals by observing their skulls and bones!


Sources:

Searfoss, Glenn. Skulls and Bones. Mechanicsburg: Stackpole Books, 1995

White, R. S. Animal Skulls. A guide for Teachers, Naturalists, and Interpreters. Tucson: International Wildlife Museum, 2002.

Meaghan Murphy
AMC Naturalist