13 



It seems to us that the common ancestors of the Scincogekkonomorpha and 

 the Iguanomorpha had a special type of locomotion, not observed in its 

 entirely in any modern groups of lizards: they had terrestrial mode of life, 

 while moving the the body was held high above the substrate (as in the Iguano- 

 morpha and the Gekkota), the proximal segments of the limbs moved in an 

 almost horizontal plane (as in Gekkota and Scincomorpha) . Locomotion was 

 slow and clumsy. The body and tail of these animals were relatively short, 

 but the limbs comparatively long. Individual features of this original 

 pattern of locomotion have been largely retained in extant terrestrial geckos. 

 As a whole the Gekkota underwent specializations in parallel with the Iguano- 

 morpha toward adaptation for climbing (an arboreal or saxicolous form of 

 life). All Iguanomorpha in the course of evolution probably passed through 

 an arboreal stage and only secondarily gave rise to desert terrestrial forms 

 such as Sceloporus and Phrynocephalus . As a result of this their pectoral 

 girdle and forelimbs were strongly modified. 



The method of movement of Scincomorpha is, perhaps, the most biologi- 

 cally progressive among the modern lizards and arises from a locomotion 

 pattern similar to that which is observed in terrestrial geckos. 



Figure 8. Phylogenetic tree (after Camp, modified by V. B. Sukhanov) 



It has already been said that the above facts do not agree with Camp's 

 classification of lizards. We feel it is necessary to modify his phyloge- 

 netic tree (Fig. 8). Dividing the lizards into the Ascalabota and the 

 Autarchoglossa must be considered wholly artificial. The Gekkota and Scinco- 

 morpha are different branches of one evolutionary lineage (division Scinco- 

 gekkonomorpha): their common ancestors possibly passed through a long 

 evolutionary path separate from that of the Iguanomorpha (division Iguano- 

 morpha) which represents a second evolutionary lineage of lizards. Division 

 of the common trunk of lizards into these two groups can, probably, be dated 

 to the Upper Jurassic and the divergency of the Gekkota and Scincomorpha to 

 the Upper Cretaceous or Paleocene. The similarity between the Gekkonomorpha 

 and the Iguanomorpha results principally from parallel or convergent evolu- 

 tion and not to close kinship. 



