Evolution and development of the mammalian jaw joint: Making a novel structure

Abstract

A jaw joint between the squamosal and dentary is a defining feature of mammals and is referred to as the temporomandibular joint (TMJ) in humans.Driven by changes in dentition and jaw musculature, this new joint evolved early in the mammalian ancestral lineage and permitted the transference of the ancestral jaw joint into the middle ear. The fossil record demonstrates the steps in the cynodont lineage that led to the acquisition of the TMJ, including the expansion of the dentary bone, formation of the coronoid process, and initial contact between the dentary and squamosal. From a developmental perspective, the components of the TMJ form through tissue interactions of muscle and skeletal elements, as well as through interaction between the jaw and the cranial base, with the signals involved in these interactions being both biomechanical and biochemical. In this review, we discuss the development of the TMJ in an evolutionary context. We describe the evolution of the TMJ in the fossil record and the development of the TMJ in embryonic development.We address the formation of key elements of the TMJ and how knowledge from developmental biology can inform our understanding of TMJ evolution.

Repair and remodeling of the mandibular head of the condylar process in four immature dogs

“…There are notable similarities between regeneration of the mandibular head of the condylar process and the evolutionary development of the TMJ in mammals (41). The development of the TMJ appears to be linked with the preceding evolutionary modifications in the dentition of early mammals (41).…”

“…There are notable similarities between regeneration of the mandibular head of the condylar process and the evolutionary development of the TMJ in mammals (41). The development of the TMJ appears to be linked with the preceding evolutionary modifications in the dentition of early mammals (41). These alterations in the dentition imposed added stress on the primary jaw joint, leading to the emergence of supplementary bone structures designed to provide support for the mandible during mastication (41), culminating in the formation of the TMJ.…”