In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral component of the dermal roof and is typically thin compared to other skull bones.
The squamosal bone lies ventral to the temporal series and otic notch, and is bordered anteriorly by the postorbital. Posteriorly, the squamosal articulates with the quadrate and pterygoid bones. The squamosal is bordered anteroventrally by the jugal and ventrally by the quadratojugal.
Function in reptilesEdit
Anatomy in synapsidsEdit
In non-mammalian synapsids, the jaw is composed of four bony elements and referred to as a quadro-articular jaw because the joint is between the articular and quadrate bones. In therapsids (advanced synapsids including mammal), the jaw is simplified into an articulation between the dentary and the squamous part of the temporal bone, and hence referred to as a dentary-squamosal jaw.
In mammals, the quadrate bone evolves to form the incus, one of the ossicles of the mammalian ear. Similarly, the articular bone evolves to form the malleus. The squamosal bone migrates and lengthens to become a new point of articulation with the lower jaw (at the dentary bone).
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- Roemer, A. S. (1956). Osteology of the Reptiles. University of Chicago Press. p. 772.
- Carr, Steven M. (2005). "Quadroarticular vs Dentary-Squamosal jaw". Memorial University of Newfoundland. Retrieved 2018-04-09.