

CAINOZOIC FAUNAS 197 



that occur among them contain few Invertebrate 

 remains. 



The Cainozoic era is the "age of Mammals and 

 Birds." After long stagnation in the Mesozoic, the 

 warm-blooded descendants of Permian Theromorphs 

 and Triassic Dinosaurs have, by deferred neanic accelera- 

 tion, amply and worthily assumed the sovereignty abdi- 

 cated by senescent Reptiles in the Cretaceous period. 

 But in the humbler sphere of Invertebrate life a com- 

 parable revolution can be recorded. The teeming 

 Rhynchonellas and Terebratulas of the Mesozoic are 

 reduced to insignificant numbers ; Trigonias and many 

 other Prionodesmacean Bivalves suffer a like fate; 

 Pleurotomarias sink almost to extinction ; Ammonites 

 have entirely gone, and Belemnites are represented 

 by scarce, usually small, descendants that bear little 

 superficial resemblance to their predecessors. Many 

 of the dominant Cainozoic types appeared in previous 

 epochs (like the Mammalia), but postponed active 

 specialization until the Eocene. Most of the Teleo- 

 desmacean Pelecypoda, Ctenobranchiate and Pulmonate 

 Gastropoda, and Nummulitid and Globigerinid Foramini- 

 fera belong to this class. " Cake-Urchins " and " Sand- 

 Dollars " (Clypeastroids) are exclusively Cainozoic, while 

 burrowing " Heart-Urchins" (Spatangids), though locally 

 abundant in the Cretaceous, are essentially Tertiary 

 forms. 



It is appropriate in this place to lay emphasis on the 

 fact that there is no contrast between existing faunas and 

 those of preceding Cainozoic periods that can compare 

 with that distinguishing Eocene from Cretaceous groups. 

 There is no Palaeontological warrant for recognition 

 of a (t Quaternary " era. Indeed, it may be doubted if 

 Cainozoic history has yet reached its middle phase, 



