R. 8. Lull — Mammals and Horned Dinosaurs. 327 



ditions, whatever their nature may have been. The inference 

 is therefore natural that the known mammals do also, and hence 

 may not represent very completely the full aspect of mam- 

 malian life at that time. Exception has been taken to this 

 statement, as the mammals are associated with an abundance 

 of fresh-water fish scales, and as all are comminuted it means 

 that the bones are drifted from a long way. Therefore one 

 may have all sorts of mammals here. The ceratopsian skulls, 

 from the extensive cavities which they contain and which must 

 have tilled with the gases incident to decay and thus become 

 highly buoyant, were doubtless also extensively drifted, a point 

 which the almost invariable lack of teeth in the upper jaws cor- 

 roborates. Hence it would seem as though the fossil contents 

 of these beds may have been the accumulation of the moribund 

 flotsam of a considerable area, but still possibly of compara- 

 tively uniform environmental aspect. The wonderful preserva- 

 tion of the tiny cusps of many of the mammalian teeth does 

 not indicate extensive rolling or disturbance after they were 

 shed from the drifting carcass, but on the other hand, many of 

 the sliver-like bone fragments found point to the dry disinte- 

 gration of the bones before burial. Were the full Lance 

 fauna known, it is probable that more of the precursors of the 

 basal Eocene mammals would be found therein. 



Summary. — To summarize : the Lance mammals are far 

 removed in time from those of the Morrison, but because of 

 the persistence of certain static Mesozoic types and the absence 

 of known Tertiary forms in the former, there is a nearer 

 resemblance in general character than between the Lance and 

 basal Eocene. Comparison between the Belly River and the 

 Lance is less satisfactory because of the dearth of mammalian 

 fossils from the former and older formation, but, as Matthew 

 says (1914, p. 391), the faxina of the Belly River is of the same 

 facies (faunal aspect) as the Lance, despite the gap represented 

 in the progressive evolution of the Ceratopsia and other dino- 

 saurs. The Belly River mammals are doubtfully more primi- 

 tive in stage and there is no good evidence of any change of 

 fauna or of the appearance of any new immigrant groups. 

 This last apparent fact may be due, however, to the dearth of 

 our knowledge of Belly River types. 



The Paskapoo and the Lance correspond closely in certain 

 aspects of their faunae, in that they have several types in com- 

 mon. These are, however, persistent Mesozoic forms, while 

 the distinguishing animals of the Paskapoo are of decided 

 Palseocene aspect. The Lance and the Fort Union show cer- 

 tain types in common, but they are again the static Mesozoic 

 phyla which have persisted through long ages with so little 

 change. The general faunal aspect has changed as materially 

 as with the Lance and Puerco and Torrejon, though, as Mat- 



