Sunday, November 30, 2014

Intramandibular joint

Basal paraves and pterosaurs do not have a intramandibular joint. 
Dinosaurs do have a intramandibular joint.

The unusual intra-mandibular joint described above is found only in herrerasaurids and theropods among dinosaurs. Dinosaurian outgroups (pterosaurs, crurotarsal archosaurs) also lack an intra-mandibular joint.


Page 21:
[Archaeopteryx] does not appear to have had an intramandibular joint
.....intramandibular articulation something that is actually absent in Archaeopteryx, but found in many of its theropod relatives.[2]


It would not tax the imagination to engender a long list of obstacles for the now dominant model of a theropod origin of birds, including....the sliding lower jaw joint [sliding intramandibular joint] of theropods (absent in birds)
The traits uniting Theropoda seem to include:
An intramandibular joint between the dentary and post-dentary bones: this may have served as a shock absorber while feeding on live prey. (Herrerasaurs have a slightly different configuration of the intramandibular joint, and thus may be convergent.)
the analysis of Benton (2004) demonstrated that the only unequivocal synapomorphy diagnosing Theropoda is the presence of an intramandibular joint.
intramandibular joint absent


  1. For future reference:
    Page 135
    Symmetric feathers twist.

    In the mid-length, the mandible is divided by the intramandibular joint. The articular, angular, surangular and coronoid are incorporated into the caudal structural unit, while the splenial and dentary form the rostral one.

    In theropods and Archaeopteryx (both mandibles of JM2257) the long, slender but strong anterior process of the angular lies in a long, subhorizontal groove of the splenial. The action of this joint has not been analyzed in detail, but vertical rotation of the dentary-splenial unit upon the posterior mandible appears to be favored.