thetical. However, paleontology can now throw some light on the time of 

 appearance of large groups of lizards. Iguanidae and Agamidae are foimd in 

 the Upper Cretaceous (Hoffstetter, 1955; Huene , 1956) and according to some 

 data in the Upper Jurassic (Bavarisaurus - Hoffstetter, 1953). Well differ- 

 entiated representative of the Gekkonidae, Scincidae and Lacertidae are found 

 only in the Upper Eocene. Some Upper Jurassic and Cretaceous taxa 

 (Hoffstetter, 1953 - Yabeinosaurus , Broilisaurus ) cannot currently De differ- 

 entiated from the Gekkota and Scincomorpha. This indicates the possibility of 

 the Iguanomorpha diverging early from the common triinJc of lizards, perhaps in 

 Upper Jurassic. But differentiation of the main evolutionary line of 

 Lacertilia into Gekkota proper and Scincomorpha could hardly have occurred 

 earlier than the Upper Cretaceous. 



A study of the musculature of the locomotor apparatus of lizards shows 

 that the Gekkota and Scincomorpha share a whole series of relatively primitive 

 characters . 



.-^" 



The clavicle in the majority of the Gekkonidae, Scincidae and Lacertidae 

 is broad and perforated ventrally by a large fenestra. In the higher Scinco- 

 morpha, the clavicle becomes hook shaped because of the reduction. In the 

 Iguania a hook-shaped clavicle is known in only three genera (Basiliscus, 

 Laemanctus - Boulenger, l855), Lyriocephalus (Siebenrock, l895); all other 



forms have a rod-shaped clavicle. 

 Evidently, in the higher Scinco- 

 morpha and all Iguania there is a 

 parallel reduction of clavicles , 

 much further advanced in the lat- 

 ter group, perhaps because of the 

 greater expanse of time (Upper 

 Jurassic to Recent). The reduc- 

 tion of clavicles in Scinco- 

 morpha may have begun relatively 

 recently. In connection with the 

 clavicular changes, there are 

 changes in the m. deltoideus. In 

 all representatives of the scinco- 

 gekkonomorphic evolutionary line, 

 some muscle fibers originate from 

 the outer surface of the clavicle 

 (Fig. 2, A). They extend an- 

 teriad round the front of the 

 clavicle, join with fibers origi- 

 nating from the clavicle's inner 

 surface, and extend posteriad 

 adjacent to the fibers originat- 

 ing from the scapula. In the 

 agamids (Fig. 2, B) the muscle 

 fibers originate on the outer 

 sirrface of the rod-shaped 

 clavicle and extend directly to 

 the scapula without curving in 

 front of the clavicle. 



Figure 2. 

 of the m. 

 lizards. 



Illustration of the position 

 deltoideus to the clavicle in 



A - Lacerta ocellata - this type of 

 deltoideus origin from the clavicle 

 occurs in Gekkonidae, Scincidae and 

 Lacertidae; B - Phrynocephalus mystaceus 

 - this type is common in iguanids and 

 agamids. CI - clavicula, H - humerus, 

 Sc - scapula, dl - m. deltoideus. 



