Eodicynodon was a medium-sized dicynodont, at about 450 mm long and 150 mm high. While it had many features common to all dicynodonts, such as canine tusks and jaw structures related to the "cheek pivot system" of mastication, it also displayed a number of ancestral features more similar to some of its primitive therapsid relatives, which are listed below.
Palate/snout While the
premaxillary bones are fused in more derived dicynodonts, a thin suture extending dorsally up from the palatal facet reveals that they are paired in
Eodicynodon, an ancestral feature they share with their primitive relatives
Venyukovia,
Otsheria, and
Pelycosauria.
sphenacodont pelycosaurs,
cotylosaurs, and Venyukovia.
Mastication Dicynodonts were specialized herbivores that employed a unique “cheek pivot system” of mastication that created powerful shearing action upon closure of the jaw and subsequently ground mouth contents through a system of interlocking ridges and grooves formed from the palate and dentary. Two morphological features, present already in
Eodicynodon, made this motion possible. The first was a double convex jaw joint, wherein both the quadrate and articular formed convex condyles. As the jaw closed, the articular condyle of the lower jaw slid anterio-dorsally along the quadrate condyle, resulting in closure of the mouth from back to front as the posterior end of the mandible was elevated dorsally relative to the anterior end. Forward slide of the lower jaw was limited by the second morphological feature unique to dicynodonts, a pivot point created between the dentary groove and palatal notch upon closure of the jaw. The lower jaw would then move so that the articular condyle slid anterio-ventrally along the quadrate condyle, which would cause the mandible to pivot in such a way that the front of the mouth closed and the back opened. == Discovery and geology ==