406 DARWINISM chap. 



Cretaceous, when they gave way to the true osseous fishes, 

 which had first appeared in the Jurassic period, and have con- 

 tinued to increase till the present day. This much later 

 appearance of the higher osseous fishes is quite in accordance 

 with evolution, although some of the very lowest forms, the 

 lancelet and the lampreys, together with the archaic ceratodus, 

 have survived to our time. 



The Amphibia, represented by the extinct labyrinthodons, 

 appear first in the Carboniferous rocks, and these peculiar forms 

 became extinct early in the Secondary period. The labyrin- 

 thodons were, however, highly specialised, and do not at all 

 indicate the origin of the class, which may be as ancient as the 

 lower forms of fishes. Hardly any recognisable remains of our 

 existing groups — the frogs, toads, and salamanders — are found 

 before the Tertiary period, a fact which indicates the extreme 

 imperfection of the record as regards this class of animals. 



True reptiles have not been found till we reach the Per- 

 mian where Prohatteria and Proterosaurus occur, the former 

 closely allied to the lizard-like Sphenodon of New Zealand, 

 the latter having its nearest allies in the same group of 

 reptiles — Rhyncocephala, other forms of which occur in the 

 Trias. In this last-named formation the earliest crocodiles — 

 Phytosaurus (Belodon) and Stagonolepis occur, as well as the 

 earliest tortoises — Chelytherium, Proganochelys, and Psepho- 

 derma.^ Fossil serpents have been first found in the Cre- 

 taceous formation, but the conditions for the preservation of 

 these forms have evidently been unfavourable, and the record 

 is correspondingly incomplete. The marine Plesiosauri and 

 Ichthyosauri, the flying Pterodactyles, the terrestrial Iguan- 

 odon of Europe, and the huge Atlantosaurus of Colorado — 

 the largest land animal that has ever lived upon the earth ^ — 

 all belong to special developments of the reptilian type Avhich 

 ■flourished during the Secondary epoch, and then became 

 extinct. 



^ For the facts as to the early appearance of the ahove named groups of 

 reptiles I am indebted to ]Mr. R. Lydekker of the Geological Department of 

 the Natural History Museum. 



2 According to Professor Marsh this creature was 50 or 60 feet long, and 

 when erect, at least 30 feet in height. It fed upon the foliage of the 

 mountain forests of the Cretaceous epoch, the remains of which are preserved 

 with it. 



