In the past decades, many different hypotheses were made on the possible function of the postorbital bar.
Three of them are commonly cited.
External trauma hypothesis Prince and Simons offered the external trauma hypothesis, where the postorbital bar protects the orbital contents from external trauma. However, a few years later Cartmill offered a new view on this bone and came up with the
mastication hypothesis. Greaves suggests that the bar strengthens the relatively weak
orbital area against
torsional loading, imposed by bite force in species with large
masseter and
temporalis muscles. However the orientation of the
postorbital process does not match the direction of the forces mentioned by Greaves.
Position hypothesis Cartmill suggests that in small mammals with large eyes and relatively small temporal fossae, where the
anterior temporal muscle and the
temporalis fascia are pulled to a more lateral position with increasing orbital convergence (front-facing eyes), the tension caused by the contraction of these muscles would distort the orbital margins and disrupt
oculomotor precision. Heesy shows that the postorbital bar stiffens the lateral orbit. Without a stiffened lateral orbit, deformation would displace soft tissues, when contraction of the anterior temporalis muscle takes place, thus impeding eye movement. == Occurrence ==