304 ORIGIN OF LIFE IN AMERICA 



belonging to the two genera Gonatodes and Phyllodactylus. 

 The single species of Gonatodes is most closely allied to a 

 species found in the West Indies, while the genus also occurs 

 along the coast of Ecuador and Peru. Of the five species 

 of Phyllodactylus, four are peculiar to the Galapagos archi- 

 pelago and more or less nearly related to P. tuberculosus, the 

 non-peculiar species being distributed along the west coast 

 of Mexico, Central and South America as far as Ecuador. 

 All the species of Tropidurus, a genus belonging to the family 

 Iguanidae, are peculiar and closely related forms, most of 

 them being confined to different islands. The genus is prin- 

 cipally found in Peru and Ecuador. The two very large lizards 

 which Darwin observed really belong to distinct genera. Two 

 species of Conolophus are now recognised, while the aquatic 

 form still retains the original name of Amblyrhynchus cris- 

 tatus. , Both genera of Iguanidae are quite peculiar to the 

 archipelago and distantly related to a South American genus. 

 Finally, the snake Dromicus biserialis, which is met with on 

 seven of the islands, is nearly akin to D. chamissonis of Chile 

 and Peru. 



The reptiles thus exhibit affinity with those inhabiting 

 western South America, Central America and the West Indies. 

 If they had reached the Galapagos islands by means of marine 

 currents, as has been alleged, one may be tempted to ask the 

 same question as I put before Why should practically all the 

 species belong to ancient types ? Giant tortoises seem to have 

 become extinct on the continents in Miocene times, while the 

 lizards of the archipelago belong to the two families Gecko - 

 nidae and Iguanidae. Although no fossil representatives of the 

 Geckonidae are known, the resemblance of their vertebrae to 

 those of the Palaeozoic Microsauri has been commented upon 

 as indicating their ancient lineage. The genus Phyllodactylus 

 occurs in tropical America, in Africa, Madagascar, Australia 

 and on Norfolk and Lord Howe's islands in the Pacific. A 

 single species inhabits the western Mediterranean region. The 

 distribution of the genus, therefore, is suggestive of a very 

 remote origin. Of the Iguanidae, as I have already pointed 

 out, (p. 127), we know that they lived in America in Creta- 

 ceous, and in Europe in Eocene times, while at present they 

 are confined to North and South America with the outlying 



