PEDIGREES AND RELATIONSHIPS 27 



merged. The Pelycosauria, which, as already said, formed a 

 specialised side branch from the rhynchocephalian stock, appear 

 to have waxed and waned within the duration of the Permian 

 period, when they were represented on both sides of what is now 

 the Atlantic. 



The mantle of the Rhynchocephalia may be said, however, 

 to have fallen on the Squamata (lizards and snakes), which is 

 at the present day the most numerously represented of all rep- 

 tilian orders, holding a position in the class analogous to that 

 occupied by the perching birds in the class Aves. Here, then, 

 we may trace a parallel as regards evolutionary history between 

 the anomodonts on the one hand and the rhynchocephalians on 

 the other. As mammals — the descendants of the anomodonts 

 — after passing through a long epoch when they were, so to 

 speak, under a cloud, eventually rose to pre-eminence, so the 

 Squamata, after a period of subordination, eventually attained 

 the dominant position among reptiles of to-day. If we regard 

 birds as likewise the direct descendants of the rhynchocephalians, 

 the parallelism between that group and the anomodont-mammal 

 line is still more remarkable. 



As to the epoch when the rhynchocephalian type blossomed 

 out into that of the Squamata we are still in the dark. If the 

 Acrosauria formed the connecting link, the evolution must have 

 been during or later than the Upper Jurassic. Squamata are 

 known from the Cretaceous, but as these (Dolichosaurus) are 

 marine types they almost certainly imply the existence of earlier 

 terrestrial forms, unless indeed they be independently derived 

 from the aquatic rhynchocephalian Champsosaiirus. From the 

 early Tertiary remains of both lizards and snakes are known : 

 and since the Egyptian Lower Eocene Gigautophis cromeri was 

 of very large size, it is practically certain that there were earlier 

 types of inferior dimensions. 



The belodonts, or Parasuchia, appear to have been solely of 

 Triassic age. The ichthyosaurs, on the other hand, ranged from 

 the Trias to the Upper Cretaceous, and may possibly have 

 survived in some parts of the globe into the earliest Tertiary. 

 Even the Triassic forms appear to have been marine, and we 

 have consequently yet to find the connecting links between 

 this group and earlier reptiles. The members of this order had 

 attained their maximum development in point of size as early 



