THE MISSISSIPPIAN PERIOD 607 



The Kinderhook fauna. The Kinderhook fauna of the great 

 Mississippian sea varied from region to region, apparently in 

 response to different physical conditions. But few of its features 

 need be noted here. 



In this fauna are found the beginnings of the great deployment 

 of the crinoids, which reached its climax later in the period, but 

 other forms of echinoderms were not abundant. The brachiopods 

 were transitional between those of Devonian and Later Mississippian 

 types. Among them, the genus Productus was conspicuous (Fig. 

 429). Not a few Devonian species may be named as the probable 

 direct ancestors of Kinderhook species, while some Devonian species 

 still lived. Mollusks were prominent, the pelecypods (i, /, Fig. 429) 

 alone having a larger number of species than the echinoderms or 

 the brachiopods. Among them are species indistinguishable from 

 those of the Waverly fauna that lived east of the Cincinnati 

 island. The gastropods were less abundant, and among them the 

 capulids, conspicuous among the gastropods of the Devonian, were 

 common. The chief representatives of the cephalopods were the 

 goniatites and although not abundant, they show a notable advance 

 over any of their known ancestors, in the more highly complicated 

 lobing of the suture. Tnlobites were few and small. Their high 

 stage of ornamentation had passed, and the day of their disappear- 

 ance was drawing near. Among corals cup-shaped forms were 

 most common. Fishes, especially sharks, were abundant. 



The Osage fauna. The physical conditions of the Osage epoch 

 present the key to the character of its fauna. Its extended shallow 

 sea, relatively free from silt, afforded a favorable field for the 

 evolution of the varied assemblage of forms that had come together 

 in the preceding epochs under less favorable conditions. There 

 is evidence also of rather free migratory communication with the 

 Eurasian continent, since many identical and allied species were 

 common to America and Europe. 



No single group so well characterizes the Osage fauna and ex- 

 presses its dependence of physical conditions as the crinoids, whose 

 abundance and diversity were climacteric (Fig. 430). The rapid 

 decline after this epoch is one of the most remarkable incidents in 

 the life history of the invertebrates. In the day of their glory, 



