Quadrate bone

The quadrate bone forms the lower jaw articulation in all classes except mammals.

In certain extinct reptiles, the variation and stability of the morphology of the quadrate bone has helped paleontologists in the species-level taxonomy and identification of mosasaur squamates [2] and spinosaurine dinosaurs.

[citation needed] In snakes, the quadrate bone has become elongated and very mobile, and contributes greatly to their ability to swallow very large prey items.

[4] In mammals, the articular and quadrate bones have migrated to the middle ear and are known as the malleus and incus.

[5][6] Along with the stapes, which is homologous to some reptilian and amphibian columellae, these are known as the ossicles and are a defining characteristic of mammals.

A schematic of an anapsid skull showing the location of major dermal bones of the upper skull, including the quadrate bone (q).
An exploded python skull with disarticulated upper and lower jaws. The quadrate bone (c) is particularly elongated in snakes, to facilitate cranial kinesis . Courtesy of the Peabody Museum of Natural History, Division of Vertebrate Zoology, Yale University.