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).

Figure 2. The mechanics of suction feeding in an aquatic larval salamander. The generation of suction requires very rapid expansion of the mouth and throat (pharynx) cavities by retraction and depression of the hyobranchial skeleton (shaded). This creates a negative pressure within the mouth. When water rushes in to equilibrate inside and outside pressures, small prey items are drawn in along with it. After capture, the mouth is closed and the pharynx compressed so that water is expelled either posteriorly through open gill slits, or anteriorly through the teeth. A very similar system is used by all suction feeding tetrapods. (a) The skull and hyobranchial apparatus in lateral view, at rest on the left and retracted on the right; (b) the skull and hyobranchial apparatus shown as mechanical units connected and moved by muscles (black lines); (c) oblique view from below showing the movements of the hyobranchial apparatus in three dimensions. Reproduced with permission from Deban and Wake (2000), copyright Academic Press/Harcourt, Inc.

Figure 3. Hyolingual projection in a salamander, Hydromantes supramontis (Plethodontidae). The projectile includes the tongue pad (enveloping a fly on the rock) as well as the hyobranchial apparatus and retractor musculature. Tongue projection has evolved several times independently in salamanders and in frogs and also in chamaeleonid lizards. In chameleons, the tongue is projected off an extended hyobranchial skeleton and in frogs the tongue is attached at the front and flipped over the lower jaw; the hyobranchial apparatus does not participate directly in projection. Photograph by Stephen M. Deban. Reproduced with permission from Wake and Deban (2000), copyright Academic Press/Harcourt, Inc.

Figure 4. Three stages of feeding in a small crocodile, Caiman crocodilus, based on X-ray movies. The prey item is shown as a stippled oval and the hyolingual apparatus (tongue plus hyobranchial skeleton) is shaded. Frames 1 to 4 for each sequence show the slow-opening phase, frame 5 is maximum gape, and frame 6 is the following jaws closed position. Frame 7 shows the crushing phase in the killing/crushing sequence and the beginning of the next jaw-opening cycle in the other two sequences. The numbers represent elapsed time in milliseconds. Note that all stages of feeding require coordination of jaw and hyolingual movements, as is typical for most tetrapod feeding. Reproduced with permission from Cleuren and De Vree (2000), copyright Academic Press/Harcourt, Inc.

Figure 5. Tongue protrusion and lingual prey capture in an iguanian lizard (Pogona barbata, Agamidae). During prey capture (ingestion), the tongue is protruded beyond the lower jaw and curled downward so that its dorsal (top) surface is presented toward the prey item. Long, sticky papillae provide an adhesive surface to which the prey adheres for rapid retraction into the mouth. Reproduced with permission from Schwenk (2000b), copyright Academic Press/Harcourt, Inc.

Figure 6. A python (snake) skull showing adaptations for swallowing large prey. Most important is the ability of the mandibles to separate at the front. Unlike most tetrapods in which each half of the mandible is fused to the other by a tight joint called a symphysis, in snakes the halves remain unfused and joined only by soft, elastic tissue (S_im). The effective length of the mandibles, and therefore the size of the gape, is also increased by adding to it mobile and elongate bones of the upper jaw, the quadrate (Qu) and supratemporal (St). These traits permit the jaws of ‘advanced’ snakes to spread very wide, enabling them to swallow large-diameter prey (D_p). In addition, left and right upper jaw bones are independently mobile, so that the snake can literally ‘walk’ its head over the prey item (a form of cranial kinesis). Reproduced with permission from Cundall and Greene (2000), copyright Academic Press/Harcourt, Inc.