15.1. Supporting structure

With the exception of birds, teeth are of primary importance for biting and chewing in most species of vertebrates. The arrangement of number, size and position of teeth in a species is called dentition. An amazing diversity of dentitions emerges as one compares animals of different groups.

Supporting bones

In humans, teeth are supported by the maxillary bone and the mandible. The alveolar processes of these bones form multiple alveoli, which are the sockets that fit the teeth. In other mammals and reptiles, the maxillary bone is not fused to the premaxillary bone. The maxillary bone supports the molar, premolar and canine teeth, whereas the premaxillary bone supports the incisors.

In lobe-finned fishes and the early fossil tetrapods, the bone homologous to the mandible of mammals is merely the largest of several bones in the lower jaw. It is called dentary bone and it forms the body of the outer surface of the jaw. It is bordered below by a number of splenial bones, while the angle of the jaw is formed by a lower angular bone and a suprangular bone just above it. The inner surface of the jaw is lined by a prearticular bone, while the articular bone forms the articulation with the skull proper. Finally a set of three narrow coronoid bones lie above the prearticular bone. As the name implies, the majority of the teeth are attached to the dentary, but there are commonly also teeth on the coronoid bones, and sometimes on the prearticular as well

This complex primitive pattern was simplified in modern vertebrates. In teleost fishes, only the dentary, articular, and angular bones remain. In amphibians, the dentary is accompanied only by the prearticular and in salamanders, by one of the coronoids. The lower jaw of reptiles has only a single coronoid and splenial, but retains all the other primitive bones except the prearticular and the periosteum.

While, in birds, these various bones have fused into a single structure, in mammals most of them have disappeared, leaving an enlarged dentary as the mandible. Finally, the lower jaw of cartilaginous fishes, is not homologous to the bones found in other vertebrates. It is composed of a cartilaginous structure homologous with the Meckel's cartilage of other groups.

Figure credits

Figure 1 by OpenStax College – Anatomy and Physiology. Chapter 7.2 Fig. 12.

Figure 2 by OpenStax College – Anatomy and Physiology. Chapter 7.2 Fig. 13.

Figure 3 by AS - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4743700