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 (Phrynosoma). 
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-Pacific belt of land which was 
joined to south-western North America (Fig. 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 an 
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 biporus. It is a significant fact 
that two peculiar genera of that ancient family occur in the 
* Coe, W. R., and B. W. Kunkel, “ Californian Limbless Lizard,” 
pp. 350—351. 
