the Cretaceous-Tertiary Problem. 211 



The Cretaceous fauna consists of six families of 

 gigantic terrestrial reptiles, popularly lumped under the 

 term dinosaurs, but belonging to two distinct orders, five 

 families of chelonians, two families of crocodilians, one 

 of rhynchocephalians, and two of mammals. The range 

 of these families is shown in the accompanying table. 







Mesozoic ? Cenzoic 





> "> 1 ^ 



Geologic Eange of Vertebrate Fauna 



1 a ^ 1 si i § ^ 1 



of Upper Cretaceous 

 Judith E. = Belly E. = Ojo Alamo. 





Saurischia 



Deinodontidae 



.. X X X X 





OrnithomiinidaB 



X X X X 



Ornithischia 



Hadrosauridse 



XXX 





Iguanodontidse 



XX X 





Ceratopsidse 



XXX 





Scelidosauridae 



XXX 





Nodosauridge 



X X X X 



Chelonia 



Pleurosternidse 



X XX 





Baenidas 



X X X X X 





Plastomenidse 



X XXX 





Dermatemydidse 



X XXX 





Trionychidse 



X X X X X X X 



Plesiosaurs 





XX X 



ICHTHYOSAURS 





X X 



Squamata 



Mosasauridas 



.... 



Crocodilia 



Crocodilidse 



X X X X X 



Choristodera 



Champsosauridge 



X X X X 



Multituberculata Plagiaulacidge 



XXX XX 



Marsupialia 



Cimolestidge 



X X 



Dinosaurs are the dominant vertebrates of a Cretaceous 

 land fauna, as plesiosaurs, mosasaurs, etc., are of the 

 marine facie s. The turtles include ^ve families, one 

 of which survives to the end of the Paleocene, three to 

 the end of the Eocene (one with a few relatives still 

 living in Central America), the fifth is still abundant. 

 The crocodiles include Mesozoic marine groups, but the 

 essentially Tertiary Crocodilidse make their first appear- 

 ance in the Upper Cretaceous. The mammals are all 

 Metatheria, an essentially Mesozoic stage, and belong 

 to the marsupial and multituberculate orders. Both these 

 orders occur in the Jurassic, Lower and Upper Cre- 

 taceous, and the marsupials survive to the present day. 



