Topic summary
Lower jaw
Extracted from the Wikipedia article Mandible.
Phylogeny
The mandible of vertebrates evolved from Meckel's cartilage, left and right segments of cartilage which supported the anterior branchial arch in early fish. Fish jaws surface in species of the large arthrodire genus Dunkleosteus (fl. 382–358 million years ago), which crushed prey with their quickly articulating mouths. The lower jaw of cartilaginous fish, such as sharks, is composed of a cartilagenous structure homologous with Meckel's cartilage. This also remains a significant element of the jaw in some primitive bony fish, such as sturgeons. In reptiles, Meckel's cartilage ossifies into the (multiple) bones of the lower jaw, while mammals of the Cretaceous (145–66 Mya) had both Meckel's cartilage and a mandible.