418 THE SUCCESSION OF THE VERTEBRATE FAUNAS. 



tially modern types of sharks and skates appear ; while among 

 bony fishes, the only important groups without some represen- 

 tative seem to be the Anacanthini, Lophobranchii, Herni- 

 branchii, and Plectognathi all highly specialized. There are 

 also the first known traces of a deep-sea fish-fauna; many of 

 the Scopeloids having quite an abyssal aspect, while typical 

 members of the surviving BathythrissidaB (Istieus) and Halo- 

 sauridae (Echidnocephalus) can be easily recognized. 



The marine reptiles of the orders Sauropterygia and Ich- 

 thyopterygia are rare in Cretaceous formations, and are almost 

 replaced by aquatic lizards of the sub-orders Pythonomorpha 

 and Dolichosauria. The first of these have a very wide 

 distribution, being met with not only in the Chalk of Europe 

 and North America, but also in corresponding deposits in South 

 America and New Zealand. The land-reptiles are essentially 

 similar to those of the Jurassic, except that they become more 

 specialized and almost fantastic just before they disappear. 

 But now there seems to have been at least some temporary 

 connection again between the northern lands on which the 

 typical Jurassic reptile-fauna developed, and the southern lands 

 on which the Triassic Anomodonts had been left to pass into 

 the Mammalia. In fact, gigantic Dinosauria have spread to un- 

 doubted Cretaceous strata in India, Madagascar, and South 

 America, while in the latter country Ornithosauria and terres- 

 trial types of Crocodilia also appear; and, on the other hand, 

 another group of diminutive mammals of the Jurassic type 

 occurs in the Upper Cretaceous (Laramie Formation) of North 

 America, while very soon at the base of the Tertiary true 

 placental mammals begin to appear both in North America 

 and Europe. Very few birds are known, but most of them are 

 typical members of their class, though still retaining teeth. 



TERTIARY. 



At the close of the Cretaceous period all the flying reptiles 

 and dinosaurs, and most of the marine reptiles seem to have 

 become extinct ; and the Tertiary formations, so far as known, 

 yield only forms of vertebrata essentially similar to those of 



