202 ORIGIN OF LIFE IN AMERICA 



of being the only poisonous lizard in existence. The genus 

 Heloderma, to which it belongs, ranges from Mexico, through 

 Arizona, to western Texas. No near relations of the Gila 

 monster are known, but it possesses some distant affinity to 

 a lizard living in Borneo. 



Better known probably are the horned toads (Phrynoisoma)'. 

 Owing to their greater activity they have been able to spread 

 much further north and east of their original centre of dis- 

 persal. The horned-toads are lizards belonging to the large 

 and important family Iguanidae which has a peculiar dis- 

 tribution suggestive of great antiquity, as I have already indi- 

 cated (p. 126). I mentioned that the family lived in America 

 as far back as Cretaceous times, and that beyond that con- 

 tinent it was only known from the Fiji Islands and Mada- 

 gascar. Leaving the latter out of consideration for reasons 

 stated (p. 126), we have only to discuss the origin of the Fiji 

 members of the family. The geological history of the Poly- 

 nesian fauna will be fully dealt with in a subsequent chapter. 

 I may mention, however, that I believe in the former exist- 

 ence of an ancient circum-Paciflc belt of land which was 

 joined to south-western North America (Pig. 14), and that 

 the Iguanidae passed across this land during their wanderings 

 from America to Fiji or vice versa. 



Let us turn from the active Iguanidae, and take, as ah 

 example, a slowly-moving creature such as the Californian 

 limbless lizard Anniella. It inhabits barren sand-dunes, lying 

 buried in the sand and exposing only the anterior part of the 

 head.* Not only is it a reptile which spreads very slowly, but 

 it is eminently an animal requiring a continuous land surface 

 for its dispersal. As might be expected, the genus Anniella 

 is quite peculiar to the south-western States. No other 

 member of the family Anniellidae is known, though it is 

 closely related to the Anguidae, which are almost confined in 

 their distribution to America and Europe. 



We also possess a single species of that remarkable family 

 of burrowing lizards, the Amphisbaenidae, in lower California 

 and Mexico, viz., Euchirotes biporua. It is a significant fact 

 that two peculiar genera of that ancient family occur in the 



* Coe, W. E., and B. W. Kunkel, " Californian Limbless Lizard," 

 pp. 350—351. 



