288 ANNALS NEW YORK ACADEMY OF SCIENCES 



LACERTILIA 



Lizards arc the largest group of the Eeptilia, comprising over 1800 

 species, mostly of small size. Most of them are active animals, and a 

 large proportion are adapted to rocky and desert habitat and arid climate. 

 They are more dependent on external warnith than mammals and birds, 

 and consequently are excluded from the colder regions; their means of 

 dispersal are perhaps less limited than with mammals, if we may judge 

 from their wider distribution, for they do not appear to be of more 

 ancient origin. Unfortunately, the rarity and fragmentary nature of 

 their fossil remains stands in marked contrast with those of mammals, 

 and our evidence as to their evolution and dispersal is chiefly indirect, 

 based upon the modern distribution, and is neither conclusive nor con- 

 vincing. Such as it is, it compares fairly well with corresponding dis- 

 tribution features among the smaller Mammalia and points to the same 

 conclusions. But it emphasizes the importance of occasional over-sea 

 transportation as a factor in distribution. Gadow observes"^ in regard 

 to the Geckos, the most cosmopolitan of all lizards : 



"Although not at all aquatic, they are particularly fit to be transported acci- 

 dentally on or in the trunks of floating trees, to which they cling firmly, and 

 they can exist without food for months." 



Other groups are somewhat less easily transported in this way, and to 

 quote the same authority: 



"It is a most suggestive fact that most of those families of Reptiles, and 

 even of other vertebrates which have a wide distribution and are apparently 

 debarred from transgressing Wallace's line, are also absent from Madagascar." 



The iguanas are chiefly Neotropical, but they occur also in Madagascar, 

 in the Fiji and Friendly Islands and in the West Indies and Galapagos 

 Islands, as well as on the American continent. Fossil iguanas are re- 

 corded from the Upper Eocene and Oligocene of Europe and from the 

 Upper Cretaceous and Middle Eocene of the western States. If these 

 determinations be correct, they must formerly have been more cosmo- 

 politan. Their presence in Madagascar is most reasonably explained by 

 their former presence in Africa, which is rendered probable by the fact 

 that they occur in the early Tertiary of Holarctica, along with various 

 mammalian groups which certainly did reach Africa. Their disappear- 

 ance from the mainland of Africa may be coupled with the invasion of 

 other later developed groups, Zonurida^, VaranidiB, Lacertida^, which 



"1 Hans Gadow : Cambridge Natural History, vol. vlll, Amphibia and Reptiles. 1901. 

 The distribution data for lizards and amphibians are mostly based upon this authority. 



