PMJs and TMJs: convergence in the craniomandibular joints of crocodilians and mammals

Crocodyliforms evolved a series of key features responsible for their Mesozoic adaptive radiation. Among these is the pterygoid buttress, the characteristic hypertrophied pterygoid flange in the skull. Although historically approached simply as a palatal element, the buttress forms a prominent articulation with the mandible here referred to as the pterygomandibular joint (PMJ). The joint bears the necessary anatomical features, such as a capsule and fibrocartilage, to be considered an enthesis organ. Biomechanically, the joint acts as a fulcrum between the dentary and jaw muscle attachments and stabilizes the mandible from medial bending and long axis rotation during orthal and twist feeding. Although all jaw muscles act about the jaw joint (i.e., the quadratoarticular joint), they also create strong mediolaterally and vertically‐oriented moments about the pterygomandibular joint such that this secondarily‐acquired craniomandibular joint is heavily loaded during most feeding behaviors. The joint originates early in pseudosuchian evolution prior to the evolution of an akinetic skull, laterally‐wrapping pterygoideus muscles, sutured mandibular symphysis, secondary palate, and skull flattening suggesting it was the key factor that stabilized the mandible and released the lineage to evolve high bite forces and robust skulls. Finally, the crocodyliform pterygomandibular joint bears resemblance to the eutherian temporomandibular joint as both joints possess sesamoid‐like fibrocartilages, such as the TMJ articular disc, within evolutionarily conserved muscle attachments. Thus, crocodyliforms and mammals convergently evolved dual craniomandibular joint systems with similar joint morphologies albeit at different locations. These new findings enable significant new insights into cranial biomechanical modeling, skeletal development and vertebrate evolution.