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The quadrate bone is a
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 and
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...
bone in most tetrapods
Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...
, including amphibians
Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arb ...
, sauropsids (reptiles
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephali ...
, birds
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
), and early synapsids.
In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper part of the jaw joint. The lower jaw articulates at the articular bone, located at the rear end of the lower jaw. The quadrate bone forms the lower jaw articulation in all classes except mammals.
Evolutionarily, it is derived from the hindmost part of the primitive cartilaginous upper jaw.
Function in reptiles
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 and spinosaurine
The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, inclu ...
dinosaurs.
In some lizards and dinosaurs, the quadrate is articulated at bot