610 GEOLOGY. 



South Joggins, Dawson took thirteen skeletons representing different 

 amphibian species from a single sigillarian stump. As such stumps 

 sometimes contained land shells and myriapods, together with amphib- 

 ian skeletons, it has been inferred that such amphibians were climbers, 

 and lived on mollusks, myriapods, and similar land life. 



In certain places amphibian tracks occur in great abundance, 

 implying that the animals frequented muddy flats; in some places 

 also their remains are common; it is therefore inferred that they were 



Fig. 283. — Cross-section of the tooth of a Labyrinthodont, of later date (Triassic). 

 Mastodonsaurus giganteus, highly magnified, showing the deep intricate infoldings 

 of the walls of the tooth. (From Woodward after Owen.) 



abundant, at least locally. From their wide differences of structure 

 and their considerable specialization, it is inferred that they enjoyed 

 conditions favorable both to divergence of type and to development 

 of individual structure, and these should have been found in the new 

 field upon which, almost or quite without rivals, they had entered, — 

 the empire of the land. 



As the evolution of the amphibians constituted the ascent of the 

 vertebrate type from the water and the beginning of their dominance 

 of the land, the event may be well regarded as one of the most signifi- 

 cant in the earlier history of the earth. 



The marked development of insects. 1 — The identification of 400 



1 Scudder, Bull. No. 71, U. S. Geol. Surv., 1891, and works there referred to. 

 Brongniart, Researches pour servir a Fhistoire des Insectes Fossiles des Temps Pri- 

 maires, 1894. Dawson, J. W., Synopsis of the air-breathing animals of the Paleozoic 

 in Canada up to 1894. 



