The structure of communities may be largely a result of evolutionary changes that occurred many millions of years ago. We explore the historical ecology of squamates (lizards and snakes), identify historically derived differences among clades, and examine how this history has affected present-day squamate assemblages globally. A dietary shift occurred in the evolutionary history of squamates. Iguanian diets contain large proportions of ants, other hymenopterans, and beetles, whereas these are minor prey in scleroglossan lizards. A preponderance of termites, grasshoppers, spiders, and insect larvae in their diets suggests that scleroglossan lizards harvest higher energy prey or avoid prey containing noxious chemicals. The success of this dietary shift is suggested by dominance of scleroglossans in lizard assemblages throughout the world. One scleroglossan clade, Autarchoglossa, combined an advanced vomeronasal chemosensory system with jaw prehension and increased activity levels. We suggest these traits provided them a competitive advantage during the day in terrestrial habitats. Iguanians and gekkotans shifted to elevated microhabitats historically, and gekkotans shifted activity to nighttime. These historically derived niche differences are apparent in extant lizard assemblages and account for some observed structure. These patterns occur in a variety of habitats at both regional and local levels throughout the world.

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Use of the tongue as a prehensile organ during the ingestion stage of feeding in lizards was studied cinegraphically in seven species. Within Squamata, lingual prehension is limited to a single clade, the Iguania (Iguanidae, Agamidae and Chamaeleontidae), which includes all ‘fleshy‐tongued’ lizards. All remaining squamates (Scleroglossa) use the jaws alone for prey prehension. Lingual prehension and a ‘fleshy’ tongue are primitive squamate characteristics. Kinematically, lingual ingestion cycles are similar to previously described transport cycles in having slow open, fast open, fast close and slow close‐power stroke phases. Tongue movements are sequentially correlated with jaw movements as they are in transport. However, during ingestion, anterior movement of the tongue includes an extra‐oral, as well as intra‐oral component. Tongue protrusion results in a pronounced slow open‐II phase at a large gape distance. A high degree of variability in quantitative aspects of ingestion and transport cycles suggests that modulation through sensory feedback is an important aspect of lizard feeding. Preliminary evidence indicates an important role for hyoid movement in tongue protrusion. Our results are consistent with the Bramble & Wake (1985) model generalized feeding cycle and support their contention that specialized feeding mechanisms often represent modifications of a basic pattern, particularly modification of the slow open phase.

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Recent advances in the field of squamate reptile chemoreception have been paralleled by the growth and preeminence of cladistics in the field of systematics, but for the most part, workers in the former have failed to incorporate the conceptual and informational advances of the latter. In this paper, I attempt a preliminary rapprochement by combining the methods of phylogenetic systematics and current hypotheses of squamate relationships with an overview of squamate chemosensory biology. This purely phylogenetic approach leads to a number of falsifiable generalizations about the evolution of chemoreception in squamates: 1) Evolution of this system is conservative rather than plastic, reflecting to a large extent suprafamilial attributes rather than adaptation to local conditions; Anguimorphs are highly chemosensory and teiids show convergence with this group; 3) Tongue-flicking, a bifurcated tongue tip, a vomeronasal (VNO) mushroom body, and a complete circular muscle system in the tongue are a correlated character complex associated with the attainment, in squamates, of a direct VNO-oral connection and the loss of a VNO-nasal connection; 4) There is little support for a visual-chemosensory dichotomy within Squamata; 5) Gekkotans are allied with Autarchoglossa, both phylogenetically and in terms of chemosensory biology; 6) Iguania are highly variable in chemosensory development; iguanids represent the primitive iguanian condition, while agamids and chamaeleonids have secondarily reduced or lost their chemosensory abilities; 7) Apparent contradictions in chemosensory behavior among iguanids probably represent intrafamilial divergence; 8) Ecological correlates within Iguanidae and other taxa might be spurious, resulting from historical factors unrelated to the adaptations in question; 9) The mechanical demands of lingual food prehension have constrained chemosensory evolution in Iguania; chemosensory evolution within Scleroglossa was permitted by the liberation of the tongue from this ancestral role.

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The morphology and mechanics of feeding in Demophzs mexicanus were studied using descriptive anatomical, cinematographic and electromyographic approaches. The lower jaw has a retroarticular process extending one-third of the total jaw length, and an articulation that restricts anteroposterior movements. Muscles from three anatomically distinct sites, the temporal fossa, the lateral surface of the neck, and the subvertebral region, act to execute the bite during feeding on earthworms. Muscles in the first of these sites are comparable to the jaw adductors of other vertebrates, while those in the second two represent morphological and functional departures. l'he large interhyoideus muscle and the elongate retroarticular process are modified to function in jaw closing. The longus capitis muscles appear to act to depress the cranium at the cranio-vertebral joint, a motion that occurs simultaneously with maximum jaw closing. The latter two muscles appear to have greater importance for feeding in Demophis than do the temporal adductors, and the evolution of this specialized arrangement may be related to the demands for a reduced cross-sectional area of the head in these burrowing vertebrates.

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