86 



CENOZOIC MAMMAL HORIZONS 



border types) ; among Perissodactyla-Equinse, only 3 species ; among 

 Artiodactyla, 4 families: (a) Camelidse, EscJmtius, Camelops (2 spe- 

 cies), Camelus; (b) Dicotylidse, Platygonus; (c) Antilocapridge, Anti- 

 locapra (first appearance) ; (d) Merycodontinse (last appearance of 

 this peculiarly American subfamily, genus Capromeryx) ; among Pro- 

 boscidea, Elephas columhi, E. imperator. In the '^Rock Creek beds" 

 of Texas is found a supposed Dinocyon (BoropTiagus) or one of the 

 Ursidse. 



MIDDLE PLEISTOCENE (GLACIAL). 

 GENERAL CHARACTERS. 



Our knowledge of the American mammals now for the first time 

 becomes continental because it represents deposits in all parts of 

 North America. 



The general characters of the middle Pleistocene as a whole may 

 be summarized as follows: 



1. This long period, which will eventually be divided into faunal 

 substages, as in Europe, is distinguished negatively by the absence 

 of the lower Pleistocene mammals (1) Eleplias imperator and (2) Artio- 

 dactyla-Merycodontinse, and (3) by the gradual extinction of the 

 resident large quadrupeds. 



2. It is marked chiefly by the gradual invasion of a Eurasian hardy 

 and boreal fauna and thus distinguished positively by the first re- 

 corded appearance (1) of Ursidae; (2) of Bovidse — (a) Ovinse, (Jb) 

 Bovinse, (c) Rupricaprinse ; (3) of 3 genera of the larger northern 

 Cervidse, namely, Alces, Odocoileus, Cervus (it is noteworthy that 

 Eangifer does not appear in our mid-Pleistocene) ; (4) among Pro- 

 boscidea, Eleplias primigenius and E. columhi succeed E. imperator, 

 and the appearance of Mastodon am.ericanus is first recorded. 



3. The hardy forest and glade fauna both east and west increase 

 in number and variety, including the Cervidae and Ursidae. 



4. The resident plains and forest-border grass-eating forms (Equi- 

 dse, Camelidsp, Elephantinse) diminish in number and gradually 

 disappear. 



5. Among all the larger Carnivora and Herbivora only 3 resident 

 families, namely, the Canidse, Dicotylidae, and Antilocapridse, survive. 



6. Thus all the less hard}^ previously invading Eurasiatic, South 

 American, and native North American animals disappear. 



7. Thus again we note the gradual extinction (1) among Edentata 

 of the South American Gravigrada and Glyptodontia, (2) among 

 Perissodactyla of the indigenous North American Tapiridae and 

 Equidse, among Camelidse of Camelus, among Carnivora of the Machse- 

 rodontinse or saber-tooths; (3) among Eurasiatic forms of the Ele- 

 phantinse. 



8. The question of latitude, or more northerly, or southerly dis- 

 tribution, becomes more important on account of the increasing cold. 



