Ingestion in Reptiles and Amphibians Kiisa Nishikawa, Northern Arizona University, Flagstaff, Arizona, USA Kurt Schwenk, University of Connecticut, Storrs, Connecticut, USA The feeding stages of prey capture, ingestion, processing, intraoral transport and swallowing are accomplished in different ways in different species of amphibians (caecilians, salamanders and frogs) and reptiles (crocodilians, turtles, tuatara, lizards, amphisbaeneans and snakes – birds have diverged so much from other reptile groups that they can be considered separately). The structural and ecological diversity of amphibians and reptiles is reflected in the diversity of their feeding systems. Introduction Approximately380millionyearsago,thepiscineancestors of terrestrial vertebrates began a slow transition to life on land. Among the many challenges facing early tetrapods was how to capture and manipulate prey in the new environment.Theancestralmechanismofsuction-feeding, effective within the viscous and supportive medium of water, was unworkable in air. A mobile, muscular tongue evolved in association with the hyoid and gill arch (hyobranchial) skeleton, and was used by tetrapods to captureandswallowfoodonland.Thetongueremainsan essential part of the feeding apparatus in most terrestrial vertebrates, including living amphibians and reptiles (Figure 1), although its specific role varies from group to group. In general, feeding involves a coordinated series of cyclical movements of the tongue, jaws and hyobranchial skeleton. Some amphibians and reptiles have returned to life in water, where they have evolved suction-feeding mechanisms secondarily. In order to facilitate study and comparisons among species, scientists recognize several distinct feeding stages. Not all stages are present in every species, and one stage sometimes blends into the next, but each represents a potentially different mechanical ‘task’ performed by the feeding apparatus, involving different parts and move- ments: (1) Prey capture is the initial seizure and immobi- lization of a food item. In amphibians and reptiles, it is nearlyalwayscoincidentwith(2)ingestion,movingafood item from the environment into the mouth, usually after capture with the tongue or the jaws. (3) Processing is the mechanical reduction of a food item, usually by chewing. (4) Intraoral transport refers to the movement of the foodintothepharynxand(5)swallowingisthepassageof food from the pharynx into the oesophagus where peristalsis takes over the task of moving food through the gut. Feeding in Amphibians Amphibians include three living orders: frogs (Anura), salamanders (Urodela) and caecilians (Gymnophiona). With only a few exceptions, all species possess a tongue that is used to varying degrees during feeding. The morphology and function of the jaws and tongue vary widely,andeachgrouphasevolveduniqueadaptationsfor capturing, processing and swallowing prey. Article Contents Introductory article . Introduction . Feeding in Amphibians . Feeding in Reptiles Frogs Caecilians Salamanders Turtles Alligators and crocodiles Birds Tuatara Lizards and snakes Monotremes Marsupials Placentals REPTILIA AMPHIBIA MAMMALIA TETRAPODA Figure 1 Evolutionary relationships among terrestrial vertebrates (tetrapods). The ancestors of tetrapods were a now-extinct group of fish that probably used suction to capture and manipulate prey. Feeding form and function of the various amphibian and reptile groups are discussed in the text. Scientific names for the amphibian and reptile groups shown in the figure are as follows: frogs (Anura); caecilians (Gymnophiona); salamanders (Urodela); turtles (Testudines); alligators and crocodiles (Crocodylia); birds (Aves); tuatara (Rhynchocephalia); lizards and snakes (Squamata). 1 ENCYCLOPEDIA OF LIFE SCIENCES / & 2002 Macmillan Publishers Ltd, Nature Publishing Group / www.els.net