76 



CENOZOIC MAMMAL HORIZONS 



V. FIFTH FATJNAL PHASE. 



Fresh migrations via Eurasia — First appearance of African Proboscidea, 

 of true Felinae among the Fehdse, of short-Umbed Teleocerinae among 

 Rhinocerotoidea, animals occurring in the lower Miocene of Europe — 

 Evidence of increasing summer droughts. 



MIDDLE MIOCENE (EUROPE, ETAGES HELVETIEN, SARMATIEN, 



TORTOXIEN). 



FATJNAL CHANGES. 



1. North America. — In the formations which are now commonly 

 classed as middle Miocene, but which may prove to represent lower 

 and middle Mocene, we meet another ver}^ profound change in the 

 mammals of North America. This change is threefold : It consists (a) 

 in the occurrence of more advanced evolutionary stages, among the 

 Camelidse and Equidse especially; (&) in the extinction of many mam- 

 mals characteristic of the Harrison or upper Rosebud or lower Arik- 

 aree, which we are here considering lower Miocene; {c) in the sudden 

 appearance of a large number of new forms of African (Proboscidea) 

 and Eurasiatic (e. g., Rhinocerotidae, Telcoceringe, Pecora) origin. 

 The appearance of several modernized selenodont artiodactyls or 

 Pecora must have effected a change in the external aspects of the 

 fauna which was only less striking than that caused by the masto- 

 dons and the bulky rhinoceroses. 



2. Europe. — As regards (h) and (c), a similar extinction and sud- 

 den appearance also mark the base of the European Miocene, the 

 Langhien or Burdigalien as represented by the Sables de I'Orleanais 

 of Europe. The conclusion is that these North American middle 

 Miocene formations contain animals which first appear in the lower 

 Miocene of Europe, just as the American lower Miocene contains 

 animals which first appear in the upper Oligocene of Europe. At 

 least, this is the hypothesis on which our correlations are based at 

 present, allowing considerable time for migration from the old to the 

 new world. 



14. DEEP RIVER SEQUENCE, SCOTT; TICHOLEPTUS ZONE, COPE. 



(Figs. 1, 10; PL I.) 

 HOMOTAXIS. 



America. — This is in large part the "Loup Fork fauna" of Cope's 

 descriptions, because his materials were chiefly from this level in 

 Colorado and Oregon beds, (a) Central Plains: 1, Horizon E of 

 Hayden and Leidy; 2, "Pawnee Creek beds" of Matthew, north- 

 eastern Colorado (75 feet), immediately overling the Harrison; 

 3, "Panhandle beds" of Gidley, northwestern Texas, (h) Northern 

 Plains: 4, Upper part of Deep River sequence (Smith Creek) or 

 Ticholeptus zone (of Cope), Montana, 5, "Flint Creek beds" of 



