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 
Ti •ias. In this last-named formation the earliest crocodiles— 
Phytosaurus (Belodon) and Stagonolepis occur, as well as the 
earliest tortoises—Chelytherium, Proganochelys, and Psepho- 
derma. 1 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 2 — 
all belong to special developments of the reptilian type which 
flourished during the Secondary epoch, and then became 
extinct. 
1 For the facts as to the early appearance of the above 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, aud 
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. 
