xv. 9 LIZARDS 409 



Amblyrhynchus, found only in the Galapagos Islands, is remarkable 

 as the only existing marine lizard, though it spends much of its time 

 on shore, basking and feeding on the sea-weed left at high tide. Phryno- 

 soma, the horned toad, with spikes on the head and back, is found in 

 the deserts of North America and burrows in the sand. This is one of 

 the few ovoviviparous iguanids. 



The chameleons are highly modified arboreal lizards from Africa, 

 Madagascar, and India. Some species have casques on the head, or 

 one or more horns on the snout. The tail is prehensile and the digits 

 are arranged in groups of two and three so as to be opposable and 

 allow the grasping of branches. Chameleons live on insects, caught 

 by means of the very long tongue (Fig. 234), which has an adhesive 

 clubbed tip and is projected by a remarkable muscular mechanism. 

 Their movements are slow and deliberate, but they show considerable 

 care in stalking their prey; as they approach it their eyes, which 

 normally move independently, converge so as to bring the prey into 

 binocular vision, presumably serving to judge its distance. Their 

 powers of colour change are described on p. 410. 



The Scincomorpha are another large assemblage, including Lacerta, 

 common in Europe and North Africa, and the skinks, many of which 

 are modified for burrowing, sometimes in the sand. Many skinks 

 have well-developed limbs, but others show all degrees of limb reduc- 

 tion, either the fore- or hind-limbs, or both, being lost. The most 

 highly fossorial of all lizards, the worm-lizards or Amphisbaenidae, 

 may also belong to the Scincomorpha, though they show many 

 remarkable specializations. Their eyes are rudimentary, their tails are 

 blunt and resemble the head, and they are able to move freely in 

 either backward or forward direction. External limbs are usually 

 absent. 



The Anguimorpha contains the anguids, of which the European 

 slow-worm Anguis is a familiar limbless example, and the monitor 

 lizards (Varanus) and their allies, which are placed in the superfamily 

 Platynota. The monitors of the Old World and Australia include the 

 largest of existing lizards, one species, the Komodo Dragon, growing 

 to at least 10 ft long. They are carnivorous, killing vertebrates as well 

 as insects, and are often semi-aquatic. Three related groups, now 

 extinct, occurred in the Cretaceous. The aigialosaurs and dolichosaurs 

 were amphibious lizards of moderate size, but the later mosasaurs, 

 such as *Tylosawus, were huge creatures, sometimes 30 ft long, and 

 were highly adapted for marine life, with long jaws and paddle- 

 like limbs showing some hypcrphalangy. The strikingly coloured 



