MEYERS, J.J.*; HERREL, A.; NISHIKAWA, K.C.: Morphological Specializations of the Feeding System in Horned Lizards (Phrynosoma)

Lizards of the genus Phrynosoma have long been noted as dietary specialists, feeding predominately on various species of ants. Several studies looking at the diet of the fourteen different species of Phrynosoma have noted that there appears to be a gradation in the percentage of ants eaten by each species. As part of study looking at the form and function of the feeding system in Phrynosoma we compared the relative masses of all the jaw and hyolingual muscles in several species. A strong correlation exists between the relative mass of the jaw adductors and depressors and volume of ants eaten. Species such as P. douglassi, which have large adductor mass, have a larger percentage of other insects in their diet. Whereas species with a higher percentage of ants in the diet have smaller adductors but larger jaw openers. This transition appears to be a trade-off between between a generalist and specialist diet. Larger adductors may allow generalists to process larger, harder prey items. Ant specialists do not need to crush prey and it may be more important to open the mouth quickly when capturing small, fast prey. These observations are supported by some preliminary kinematic and bite force data in two species.