In bony fish, the quadrate and articular bones replaced the cartilage and several dermal bones covered the jaw cartilages. In tetrapods, the upper jaw alone suspends the lower jaw. This condition is metautostylic. This frees the hyomandibular of the hyoid arch from jaw suspension and it is incorporated into the ear. The number of upper and lower jaw bones progressively becomes reduced.
Mammals have only one paired bone, the dentary, in the lower jaw.
The articular and quadrate bones are jaw joints in most vertebrates but are moved to the ear in mammals.