lizard that specializes in preying on ants and is 

 so unusually shaped and well camouflaged 

 that even experienced lizard biologists have 

 difficulty spotting them. 



Of the insect-eaters, chameleons have 

 adopted the most extreme form of the am- 

 bush lifestyle. Chameleons have nearly elimi- 

 nated pursuit; instead, they have a propulsive 

 tongue that is often longer than their body 

 [see photograph on pages 34-35]. A chameleon 

 creeps within range of its insect prey, then 

 hurls its tongue explosively at it. The prey 

 sticks to the tongue, then gets rapidly pulled 

 into the chameleon's mouth. All the while, 

 the chameleon remains otherwise immobile, 

 hidden by its cryptic shape and coloration. 

 One of the main advantages of that strategy is 

 that it reduces risk: when an animal moves, 

 potential predators may see it. The strategy 

 also saves energy: shooting forth the tongue 

 "costs" less than chasing down prey. 



If there is a downside to the iguanian life- 

 style, it is being tied down to real estate that 

 matches the animal's camouflage. A lizard that 

 looks like a leaf can be nearly invisible in a 

 bush, but it stands out on a rock. So the need 

 for camouflage has doubtless played an impor- 

 tant role in the evolution of iguanian social be- 

 havior. Most iguanians are territorial, fiercely 

 defending areas where they blend in. There 

 they remain unless another of their species 

 usurps the favored place. 



Rigid skull 



Rhynchocephalian 

 (tuatara) 



quadrate bone 



quadratojugal bone 



Streptostyly 



Squamate 

 (chameleon) 



Mesokinesis 



Scleroglossan 

 (gecko) 



Prokinesis 



Serpentes 

 (puff adder) 



In sharp contrast to iguanians, scleroglossans 

 evolved in ways that enabled them to cap- 

 ture and manipulate prey with their jaws, an 

 ability that Schwenk calls jaw prehension. 

 That strategy freed up the tongue for tasks 

 other than capturing prey, and the tongue be- 

 came firmer as a result (scleroglossa means 

 "hard-tongued"). Among the early adapta- 

 tions in this group was the addition of a joint 

 in the top center of the skull that enabled the 

 upper jaw to bend upward and downward (try 

 doing that with your upper jaw!). The flexible 

 movement in the middle of the skull, known as 

 mesokinesis, greatly increased biting efficiency by 

 allowing the upper jaw to move downward as the 

 lower jaw closes from the bottom up [see illustration 

 on this page]. Snakes have a similar hinge, but it is in 

 front of their eyes (a condition known as prokinesis). 

 They also have additional flexible joints, such as one 

 at the front of the muzzle that enables the left and 

 right bones of the upper jaw and palate to move in- 

 dependently (that is what makes it possible for a 



Joints of the skull and jaws (arrows) help distinguish members of the 

 order Squamata (lizards and snakes) from one another and from 

 members of the closely related order Rhynchocephalia. Skull of a tu- 

 atara (a), a member of the order Rhynchocephalia, is relatively rigid. 

 The lower jaw pivots from the lower end of the quadrate bone 

 (green) and the adjacent quadratojugal bone. In skulls of squamates, 

 including chameleons (b), the jaw pivots from the lower end of the 

 quadrate. The upper end of the quadrate bone also enjoys some 

 freedom of movement, a condition known as streptostyly, making it 

 possible for the animal to move the rear of the lower jaw more 

 freely in manipulating prey. Many squamates have an additional joint 

 in the skull that enables the muzzle to flex upward and downward. 

 In most lizards (c), that joint is behind the eyes (mesokinesis), but in 

 snakes (d), it lies in front of the eyes (prokinesis). Snakes have other 

 flexible skull and jaw joints; the viper (d), for instance, can also ro- 

 tate its upper jaw bones that hold the fangs. 



snake to "walk" its head down over a large item of 

 prey). Another important innovation in snakes is a 

 loose, stretchable cartilaginous ligament that joins 

 the front tips of the right and left lower jawbones: 

 that allows the bones to move apart, enabling snakes 

 to swallow exceedingly large prey (recall the draw - 

 ing of a snake in The Little Prince). 



Switching from tongue to jaws for capturing prey 

 might not seem groundbreaking. The change freed 

 the tongue for other functions, however, and likely 



July/August 2006 NATURAL HISTORY 



31 



