Shifting paradigms: Herbivory and body size in lizards

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Abstract
Many lizards frequently eat fruits and flowers, but few are strictly herbivorous (1, 2). For >30 years, biologists have perpetuated the notion that herbivory in lizards required large body size, based largely on a set of physiological arguments centered on thermal requirements for digestion of plants and the observation that the few studied herbivorous lizards were relatively large in body size (3). From the outset, the argument was fundamentally flawed, because most known large-bodied herbivorous lizards are members of a strictly herbivorous clade, the Iguanidae. Consequently, a single origin of herbivory from a large-bodied ancestor accounts for much of the association between herbivory and large size in lizards. Within other lizard clades, herbivorous species are not among the largest (e.g., Teiidae, Cnemidophorus murinus, Cnemidophorus arubensis, and Dicrodon guttulatum; and Varanidae, Varanus olivaceus). Even when the few noniguanian origins of herbivory are added, the number of origins pales in comparison with those identified in this issue of PNAS by Espinoza et al. (4) in a single iguanian clade, the Liolaemidae. More importantly, the multiple origins identified by Espinoza et al. derive from small-bodied ancestors in relatively cool environments, running counter to the notion that herbivory in ectotherms requires large body size and warm environments. Why is this such an important finding, and how does it change the way we think about the evolution of feeding and diets in lizards? To fully appreciate the significance of this finding, it is necessary to recount the evolution of feeding strategies in squamate reptiles (Fig. 1). Squamate ancestors used visual cues to detect and discriminate prey, the tongue to capture and manipulate prey (lingual prehension), and an ambush …