716 GEOLOGY 



(7) Sponges and foraminifera were prolific and arc well pre- 

 served. 



(8) A marked change in the aspect of the fishes had set in dur- 

 ing the Trias, and was carried farther in this period. The cross- 

 opterygians (Fig. 486) and dipnoans were reduced, the selachians 

 continued undiminished ; the skates and rays began their modern 

 career; the Chimceridce, the existing family of sea-cats or spook- 

 fishes, made its appearance, so far as fossils show, and developed 

 notably (Fig. 487); the forebears of the living garpikes and stur- 

 geons took precedence in numbers; the forerunners of the modern 

 Amia (Fig. 488) were important, and the initial forms of the bony 

 fishes (teleosts), the dominant existing type, made their appear- 

 ance. The aspect of the class was markedly more modern than at 

 the close of the Paleozoic. 



(9) It was noted under the Trias that certain land-reptiles went 

 down to sea, and introduced a new phase of vertebrate mastery 

 over the deep. Though doubtless suffering from the new dynasty, 

 it appears that the fishes continued in notable abundance and 

 variety. It will be seen later that they outlived the invading race, 

 and resumed, in large measure, their former dominance. Some of 

 the reptiles which had taken to the sea had become extinct, while 

 others made their first appearance late in the period. The iclithi/- 

 osaurs (fish-like saurians) reached their highest development in this 

 period, and seem to have swum every sea. Their adaptation to 

 aquatic life is shown in the complete transformation of their limbs 

 into paddles (Fig. 489) , in the reduction of the outline of the body to 

 ichthic lines and proportions, in the sharp down-bending of the 

 vertebra at the end of the tail for the support of a caudal fin, in the 

 long snout set with teeth adapted to seize and hold slipping prey, 

 but not to masticate it, in the protection of the eye by bony phnes. 

 and, interestingly enough, in the development of a viviparous habit 

 that freed them from the necessity of returning to land to depo-it 

 their eggs, after the manner of sea-going turtles and crocodiles. 

 That their food consisted in part of invertebrates is evident from 

 the fossil contents of the stomachs, the remains of 200 belemnites 

 having been found in a single one. There were small as well as 

 larjie forms of ichthyosaurs some exceeding 30 feet in length. 



Descended from a different stock, the plesiosaurs adapted them- 



