Functional and evolutionary morphology of lingual feeding in squamate reptiles: phylogenetics and kinematics

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.