The chewing cycle in the herbivorous lizard Uromastix aegyptius (Agamidae)

The chewing cycle was examined using cinematography at 32 frames per second (fps) and simultaneous electromyography of selected jaw muscles. Three types of food of various sizes were fed to the animals. Seven feeding behaviours were distinguished and comparisons between the chewing cycles in these behaviours made. The basic chewing cycle consisted of 4 phases: (1) slow opening, (2) fast opening, (3) closing and (4) stationary. The timing of these phases, the maximum gape angle used and the action of the tongue varied with each type of behaviour. Differences in the timing of the chewing cycle were related to both the size and texture of the food and to tongue position. The jaw adductor muscles were active only during closing, but opening muscles were active during fast opening and occasionally also during closing. Some behaviours showed differences in the level of muscle activity. Thus, Uromastix has a complex chewing cycle similar to the mammalian one. It is suggested that the mammalian chewing cycle developed from the reptilian chewing cycle by the addition of transverse movements of the lower jaw.