74 ANIMAL LIFE PAST AND PRESENT. 



joint of the back-bone was, however, composed of three 

 separate pieces ; and since a very similar peculiarity is 

 found in certain primitive fishes, we have again evi- 

 dence of the close affinity existing between these two 

 groups of animals. 



The amphibians forming the group under considera- 

 tion made their earliest appearance, so far as our 

 present knowledge entitles us to speak, at the early 

 part of the great Coal Period. Thence they were 

 abundant in the Permian and Triassic (New Red 

 Sandstone) epochs, but in Europe appear to have 

 almost or entirely died out by the time of the 

 Oolite. In these early epochs they were widely dis- 

 tributed over the surface of the globe, their remains 

 having been obtained from all the great continents. 

 In size they varied from tiny creatures a few inches 

 in length to the giants with a skull of fully a yard in 

 length (Fig. 21). The perfect state of preservation in 

 which the skeletons of the smaller forms occur in the 

 fine-grained petroleum shales of the Continent shows 

 that in their earlier stages they were furnished with 

 external gills like modern Salamanders, thus indicating 

 that they underwent a similar metamorphosis. 



At the time that the Primeval Salamanders were 

 so abundant, true reptiles were either totally absent 

 (Carboniferous period) or represented by comparatively 

 few forms (Permian), so that the role now taken by 

 the latter was then to a great extent played by the 

 former. We may thus consider that the place now 

 occupied by Crocodiles was then held by the Masto- 



