260 C. SCHUCHERT MORRISON AND TENDAGURU FORMATIONS 



Land plants 23 Rhj-nchocephalians 1 



Fresh-water mollusks 24 Dinosaurs 75 



Practically all belong to living Theropoda 15 



genera. Iguanodonts 14 



Fishes 3 Armored forms 11 



Pterosaurs 1 Sauropoda 35 



Turtles 1 Birds 1 



Crocodiles 3 Mammals 25 



Frogs 1 



Of these fossils the only ones that can be nsed more or less successfully 

 in detailed correlation are the plants and dinosaurs. This is because they 

 have representatives^ and in some abundance, in more than two places, 

 while the other vertebrates are too scattered, often occurring in single 

 examples, to be of much value in stratigraphy. 



Evidence of the plants. — Eecently a 'few additional land plants other 

 than those mentioned above were found in the Morrison of the Big Horn 

 Basin of Wyoming. These Knowlton has determined as Nilsonia nigri- 

 collensis, a Lakota species, and Zamites arcticus, of the Kootenai, both 

 of which formations are 3'Ounger than the Morrison. He states:^* "So 

 far as they go they indicate that the Morrison is Cretaceous.^' On the 

 other hand, the small cycad (Cycadella) trunks found by Knight in the 

 Freezeout Hills, wlien compared with those from the Lakota and Patuxent 

 formations, Knowlton holds also argue for the Cretaceous age of the 

 Morrison. 



Berry,^-'^ from a detailed study of the interrelations of the plants of the 

 Wealden, Potomac, Kome, Kootenai, and Morrison formations, concludes 

 that "at least some of the Morrison must be of Low^er Cretaceous age." 

 The plants are therefore seen to be in favor of the Morrison being of 

 Comanchian age, though the evidence is not decidedly in favor of the 

 correlation. 



Evidence of the invertebrates. — It is well knoT\Ti that the fresh-water 

 mollusks have little significance in correlation, and this appears to be 

 especially true of those of the Morrison. Stanton^^ has studied these 

 shells and concludes: 



"The Morrison fauna then stands by itself, distinct from the few fresh- 

 water invertebrates that preceded it in the Triassic and distinct from the non- 

 marine Cretaceous faunas which followed it. . . . The study of these 



1* P. H. Knowlton : Note on a recent discovery of fossil plants in the Morrison forma- 

 tion. .Tour. Wash. Acad. Sci., vol. 6. 191^, i>p. 180-181. 



'^ E. W. Berry : Paleobotanic evidence of the age of the Morrison formation. Bull. 

 Geol. Soc. Am., vol. 26, 1915, p. 341. 



i«Op. cit., pp. 347-348. 



