THE PERMIAN PERIOD. 647 



ably began to differentiate from their ancestral amphibians earlier 

 than the Permian, the first demonstrable relics as yet found are from 

 the lower strata of this period. Before its close, there had appeared 

 a large and complex group of primitive reptilian forms very curiously 

 related to one another, implying that they were yet in the early stages 

 of their differentiation, and hence still retained various common inheri- 

 tances from their ancestry, and implying also, probably, that they 

 were affected by parallel evolution. There were, at the same time, 

 signs of profound divergence. Two great branches seem already to 

 have been defined in part; perhaps indeed they had never formed 

 a common group, as reptiles, but had parted company while yet they 

 were amphibians. The one (essentially the Diapsida of Osborn) 1 

 bore resemblance to the microsaurians and may have descended from 

 them or from allied forms. In the earliest phases represented, they 

 had already attained a decidedly reptilian structure of the rhyncho- 

 cephalian type. They seem to have been the forerunners of the great 

 hosts of lizards, crocodiles, dinosaurs, ichthyosaurs and flying saurians 

 that constitute the most declaredly reptilian line ; not that these were 

 all necessarily descended from the Permian rhynchocephalians, but 

 they form a great group marked by certain analogous features, 

 implying either kinship in genesis, or kinship in evolution. 



The other group (Synapsida) bore skeletal resemblances to the 

 highest labyrinthodonts, on the one side, and to the lowest mammals 



Fig. .299. — Paheohatteria longicaudata, a primitive diapsidan of the order Protorosauria, 

 about t? natural size. (Restoration by J. H. McGregor.) 



that appeared later (M onotremes) , on the other, and hence may be 

 regarded as constituting the mammalian strain of the ancestral rep- 

 tiles. In their earliest known phases they were rather anomalous, 

 and later they deployed into a remarkably complex order (thero- 



1 Science, Vol. XVII, No. 434, 1903, pp. 275-276. 



