"Dental features suggestive or indicative of high-fiber herbivory include dentitions adapted for crushing and grinding, or marginal teeth with labiolingually compressed, leaf-shaped, and cuspidate crowns suit- able for puncturing and shredding plant fodder. Features of the skull and mandible variously associated with feeding on plants, especially in mammals, include short tooth rows (along with foreshortening of the snout and mandible), elevation/depression of the jaw joint relative to the occlusal plane for increased mechanical advantage of the adductor jaw muscles, enlargement of the adductor chambers and temporal openings as well as deepening of the zygomatic arches and mandibular rami for the origin and insertion of substantial adductor jaw muscles, and jaw joints suitable for complex mandibular motion (Maynard Smith and Savage 1959; Turnbull 1970; Rensberger 1986; Janis 1995). Finally, plant-eating tetrapods typically have longer and/or bulkier digestive tracts, and a longer and/or broader trunk region, than related faunivorous forms (Schiek and Millar 1985; Dearing 1993) because part of the gut is modified to form a reservoir housing and creating suitable pH conditions for the endosymbiotic micro-organisms involved in the fermentative break- down of the cellulose from the ingested plant fodder. Passage of food through longer intestinal tracts also allows for longer periods of time for processing of resistant materials. Thus the rib cages of many herbivorous tetrapods are either much wider and more capacious (‘barrel-shaped’) than those of their closest faunivorous relatives, or the trunk region is elongated to accommodate a longer digestive tract. This is reflected in overall body proportions as well as in the structure of the vertebral column."
- Hans-Dieter Sues. Herbivory in terrestrial vertebrates: an introduction. In: Evolution of herbivory in terrestrial vertebrates perspectives from the fossil record / edited by Hans-Dieter Sues. Cambridge, U.K. ; New York : Cambridge University Press, 2000.