ANIMALS OF THE PAST 331 



modern oysters and razor-clams were in existence. The 

 presence of primitive myriapods indicates that the land had 

 a well-established fauna at this time. 



Carboniferous Period. The rocks of the coal measures 

 are of interest chiefly because they contain the remains of 

 the first known animals with pentadactyl limbs. These 

 were amphibians and some of them at least breathed air 

 into the lungs when in the adult condition. They lived in 

 fresh water and some may have been more or less terres- 

 trial. All the Carboniferous amphibians are called stego- 

 cephalians because they had the head " roof ed-over " with 

 bony plates. Some were several feet in length and a num- 

 ber had teeth of very complicated structure (labyrintho- 

 donts). Sharks were numerous and widespread at this 

 time; true fishes were increasing in numbers. 



Toward the end of the Carboniferous Period insects re- 

 lated to orthopterans, may-flies, and dragon-flies were living 

 in the land vegetation, and there were other types which 

 later became extinct. Various arachnids and a number of 

 species of myriapods were also living on land. The brachi- 

 opods and the older classes of molluscs and echinoderms 

 were declining in numbers. Only a single family of trilo- 

 bites persisted to the end of this period. The abundant 

 land vegetation was largely responsible for the coal deposits 

 that are being mined at the present time. 



Permian Period. The number of species of amphibians 

 increased somewhat during this period, but the most inter- 

 esting feature is the rise of the reptiles, which came into 

 existence in the preceding period and now invaded aquatic 

 and terrestrial habitats. Reptiles soon showed specializa- 

 tion along a number of different lines. Some Anomodontia 

 resembled mammals in many structural features, and in all 

 probability the mammals later arose from this stock. 

 Many of the old types of fishes were dying out, even that 

 which probably gave origin to the amphibians declined, 

 but their places were taken by species more like those of 

 modern times. The trilobites, so characteristic of ancient 



