ENVIEONMBNT OP THE TITAN0THEEE5 



117 



Height in feet above Pierre shale at which remains of titanotheres were found as determined in 1901 hy J. B. 



Hatcher and N. H. Barton'^ 



Skull Y' (?). "Big flat-horned skull in National Museum"; Nat. Mus. 1211 (?) 



Skull Q. Indian Draw. Probably skull "small q" was meant (Nat. Mus. 4946, Brontotherium curtum), 



' ' wrongly lettered Q" 



Large-horned red skull. Nat. Mus. 4256, Brontotherium medium (type) 



Skeleton. Am. Mus. 518, Brontops robustus? 



Skull v. Indian Draw. Nat. Mus. 4711, Megacerops copei (type) 



Long-horned skull. West branch of Indian Draw. Brontotherium ramosum 



Skull M. Near Middle Corral Draw. Nat. Mus. 4259, Brontops brachycephalus 



Skull "F." Quinn Draw, South Dakota. ?Nat. Mus. 4258, Brontops brachycephalus 



Skull O'. South side of west fork of Corral Draw. Nat. Mus. 4705, Megacerops "bucco," female 



Skull "I." Quinn Draw, South Dakota. Nat. Mus. 2151, "AUops serotinus," female 



Skull "H." Quinn Draw, South Dakota. Nat. Mus. 4251, Allops serotinus (type) 



Skull "little F." Quinn Draw, South Dakota. Nat. Mus. 4703, Brontops dispar 



Little skull "B." On fork of west fork of Corral (?Quinn, J. B. H.) Draw. Probably skull b, Nat. Mus. 



4947, Brontops brachycephalus, female, aged 



81 

 C) 

 65.4 



"93. 3 



81. 



n 



55. 6 

 71.4 

 46. 7 

 80 

 77-34 

 62 



65. 3 

 62. 3 

 55. 6 

 48. 5 

 46. 7 

 43.5 

 40.7 

 39.0 



14.4 



• In a letter to the author, dated July 31, 1901, Hatcher expressed grave doubts as to the accuracy of these levels on account of practical difficulties encountered in the 

 field. 



» From horizon ot skull O', Nat. Mus. 4705, to horizon of this skull there is a vertical upgrade of 46.6 feet. 



' 27 leet above skull V. 



•I Very high, 8 to 10 leet from top of titanothere zone (Hatcherl. 



• 32 leet below the 3-foot sihceous limestone layer at top of Titamtherium zone. The Pierre shale contact was far away, and although it was on a line of levels the dip 

 in interval could not be ascertained precisely (Darton). 



MAMMALIAN LIFE OF THE LOWER OLIGOCENE TITANOTHEEIUM ZONE 



The most highly characteristic feature of the Ohgo- 

 cene mammals as a whole, compared with the Eocene 

 mammals, is their decided modernization, which is 

 shown in the following table giving the percentages 

 of the modern and the archaic families of the Oligo- 

 cene Plains fauna as compared with those of the Eocene 

 mountain-basin fauna. 



Percentages of modern and archaic families in Eocene, Oligocene, 

 and Miocene time 



Basal Eocene 



Lower and middle Eocene 



Upper Eocene 



Lower Oligocene 



Miocene 



Modern fami- 

 lies or those 

 closely related 

 or ancestral 

 to modern 

 families 



Archaic fami- 

 lies supposed 

 to be wholly 

 extinct and 

 not closely 

 related to 

 modern types 



This modernization of mammalian life is in part 

 real and in part apparent, because the Plains fauna 

 presents for the first time the full aspect of the upland, 

 plains, and meadow life, especially the smaller and 

 larger herbivorous ungulates. This life is, however, 

 only partly revealed in the Titanotherium zone, in 

 which conditions for the fossilization and preserva- 

 tion of the land fauna were less favorable than in the 

 overlying Oreodon zone (Brule clay). In fact, re- 

 mains of the small ungulates, such as the horses of the 

 period (Mesohippus) , are very rarely preserved in 

 either the coarser or the finer sediments of the Chad- 

 ron of South Dakota but are found more abundantly 

 in the sediments of Pipestone Creek, Thompson 

 Creek, and other areas in Montana and in the Swift 

 Current Creek area of Saskatchewan. The entire 

 Titanotherium zone fauna as listed by Osborn and 

 Matthew (1909.321, pp. 103, 104) contains representa- 

 tives of 6 orders and 24 families of mammals, which 

 are of interest and value as showing the principal 

 types of mamnxals that were in competition with the 

 titanotheres in the struggle for existence. 



