Editing Synapsida (section)

===Jaw===
The jaw transition is a good [[Scientific classification|classification]] tool, as most other fossilized features that make a chronological progression from a reptile-like to a mammalian condition follow the progression of the jaw transition. The [[mandible]], or lower jaw, consists of a single, tooth-bearing bone in mammals (the dentary), whereas the lower jaw of modern and prehistoric reptiles consists of a conglomeration of smaller bones (including the dentary, [[articular]], and others). As they evolved in synapsids, these jaw bones were reduced in size and either lost or, in the case of the articular, gradually moved into the ear, forming one of the middle ear bones: while modern mammals possess the [[malleus]], [[incus]] and [[stapes]], [[Basal (phylogenetics)|basal]] synapsids (like all other tetrapods) possess only a stapes. The malleus is derived from the articular (a lower jaw bone), while the incus is derived from the [[quadrate bone|quadrate]] (a cranial bone).<ref name="Salentijn">Salentijn, L. ''Biology of Mineralized Tissues: Prenatal Skull Development'', [[Columbia University College of Dental Medicine]] post-graduate dental lecture series, 2007</ref>

Mammalian jaw structures are also set apart by the dentary-squamosal [[temporomandibular joint|jaw joint]]. In this form of jaw joint, the dentary forms a connection with a depression in the [[squamosal]] known as the [[glenoid cavity]]. In contrast, all other jawed vertebrates, including reptiles and nonmammalian synapsids, possess a jaw joint in which one of the smaller bones of the lower jaw, the articular, makes a connection with a bone of the [[skull|cranium]] called the [[quadrate bone]] to form the articular-quadrate jaw joint. In forms transitional to mammals, the jaw joint is composed of a large, lower jaw bone (similar to the dentary found in mammals) that does not connect to the squamosal, but connects to the quadrate with a receding articular bone.