136 THE AGE OF MAMMALS 



General. — The Eocene fishes of the Rocky Mountain region are partly 

 known in the Wasatch (Lower) and Bridger (Middle), and far more fully 

 in the intermediate Green River Shales, which, since they are found to lie 

 intermediate between the Wasatch and Upper Bridger, are considered of the 

 same age as the Wind River and the Lower Bridger formations. The fact 

 of most general interest is that the fishes are partly those of the existing 

 freshwaters of the interior of the United States, and partly those now char- 

 acteristic of South America, Australia, and Africa. Thus in the Bridger 

 we find the LepidosteidsB represented by the garpike (L. anax), as large 

 as the largest alligator gars of the Mississippi. In this formation, as well as 

 in the Bridger and Washakie, the other American ganoid family of bowfins 

 (Amiidse) is abundantly represented. The siluroid, or catfish, order Nema- 

 tognathi, represented in the Bridger and Washakie Rhineastes, is now widely 

 distributed in South America. This South American distribution is more 

 clearly represented in the remarkable deposits of the Green River. 



The Green River Lake Formation. — From the evidence afforded by the 

 fishes, the Green River Shales are best explainable as either an estuarine or 

 a land-locked bay deposit. On such a supposition only can we account for 

 the preponderance of river forms with a small admixture of marine or coast 

 forms, such as Notogoneus, belonging to a family (Gonorhynchidse), the 

 living members of which are all strictly marine (Cope, Smith Woodward), 

 or the sting ray, Dasyatis, a member of the order of sharks, allied to existing 

 forms which frequent the streams and estuaries of Florida as well as the 

 adjacent coasts (Boulenger). Altogether the fishes represent three major 

 groups: elasmobranchs (sting rays), ganoids (Lepidosteus, Amia), and 

 teleosts. A large part of the teleosts are related to fishes at present confined 

 to the southern hemisphere. Thus the diplomystids ('rough-backed 

 herrings') survive only in certain rivers and along portions of the coasts 

 of Chili and eastern Australia; Dapedoglossus or Phareodus and Priscacara 

 belong to families now chiefly distributed in South America, Africa, and 

 Australia. 



These Neotropical and possibly Antarctic affinities coincide with those 

 displayed in the turtles and tortoises described below (see Bridger Basin). 



The fishes thus indicate, first, that the Green River Lake still preserved 

 or had only recently lost connection with the sea, and second, that western 

 North America had enjoyed long-continued continental connection with 

 western South America. They may also be interpreted as favoring the 

 highly improbable 'Atlantis' hypothesis. 



The flora ^ also presents some indications of South American affinity in 

 Manicaria, a palm now confined to Guiana, and in Zizyphus, a tropical plant. 

 Here also we find the palms Sabal and Flahellaria, horsetails (Equisetum), 

 and among the ferns the genus Acrostichum, which is now confined to the 



> Newberry, J. S., and HoUick, A., The Later Extinct Floras of North America (edit, by 

 HoUick). U.S. Geol. Surv., Vol. XXXV, 1898. 



