194 THE CERATOPSIA. 



lower jaw, the food must have been retained within the mouth by the muscular walls of the 

 cheeks. Unless the teeth also subserved the function of food getting as well as of mastication, 

 which is questionable, it is doubtful whether the gape of the mouth had a greater backward 

 extent than the anterior end of the tooth series. This would bring the corner of the mouth 

 decidedly in advance of the position indicated by Knight in PL I. (Compare fig. 5.) 



PROBABLE ENVIRONMENT. 



T. W. Stanton in a note says: 



It is difficult to reconstruct |he physiographic conditions which prevailed in the Middle West during later Mesozcic time, 

 but it should be remembered that in that region there- was then a great shallow continental or mediterranean sea, and that 

 there were large areas so near sea level that very slight movements would bring bhem beneath the sea or partly or wholly 

 drain them, so that it is probable that shallow-water and nonmarine conditions were often extended over large areas very 

 rapidly. 



It would seem as though some such elevation, occurring at the close of the Claggett, gave 

 rise to conditions under which the fresh-water Judith River deposits could be formed and that 

 the Judith River period was succeeded in turn by a subsidence which caused an encroachment 

 of the sea upon the land, giving rise to the Bearpaw shales. Next a second diastrophic movement 

 caused a recession of the salt waters and inaugurated the conditions which characterized the 

 Laramie. 



Hatcher b thought that the period of elevation which brought about the close of the marine 

 Cretaceous was followed, during the Laramie, by a period of subsidence not sufficient to cause 

 a return to marine conditions, but such as to allow continual shallow-water deposition, as is 

 evidenced by the great number of lignite seams in the Ceratops beds and by the absence of 

 continuity of strata and the frequent cross-bedding which prevailed. Hatcher says: 



The. Ceratops beds are thought to afford evidence in themselves of having been deposited not in a great open lake, but 

 in a vast swamp, with occasional stretches of open waters, the whole presenting an appearance similar to that which now 

 exists in the interior of the Everglades of Florida. This condition would account for the frequent changes from one material 

 to another in the same horizon. ... In some places in the beds these changes are quite frequent, strata of sandstones and 

 shales replacing one another in great confusion. It would also explain the cross-bedding so often seen in the sandstones of 

 this region, in localities remote from the present border of the beds, and hence far removed from the shore of the ancient lake 

 or swamp. This cross-bedding could hardly occur in offshore deposits of a great fresh-water lake of any considerable depth. 



The conditions that prevailed over this region during the period in which the Ceratops beds were deposited were prob- 

 ably those of a great swamp with numerous small, open bodies of water connected by a network of watercourses constantly 

 changing their channels. The intervening spaces were but slightly elevated above the water level or at times submerged. 

 The entire region where the waters were not too deep was covered by an abundant vegetation, and inhabited by the huge dino- 

 saurs (Triceratops, Torosaurus, Claosaurus, etc.), as well as by the smaller crocodiles and turtles and the diminutive mammals, 

 all of whose remains are now found embedded in the deposits. 



The frontispiece admirably depicts such a scene as Hatcher has described. 



Dr. W. D. Matthew, in a recent paper, speaks of three modes of life available during the 

 Mesozoic for land vertebrates, "the amphibious-aquatic, the arboreal, and the aerial, the terres- 

 trial being subordinate because the upland flora was largely undeveloped or inedible as compared 

 with its present condition." The three provinces Matthew believed were peopled by reptiles, 

 mammals, and birds respectively. With reference to the dinosaurs in particular Matthew's 

 views are expressed in a letter to the writer, dated June 6, 1905, as follows: 



I believe that they (the dinosaurs) were a — in fact the — land group of reptiles, but that nearly all we know of them is a 

 number of aberrant amphibious or aquatic specialized branches; that the great arid subglacial period of the Perm-Trias gave 

 them their initial trend on lines parallel to the evolution of the Mammalia during the Tertiary-Quaternary; that in the late 

 Jura and the late Cretaceous a reaction to moist, torrid climate caused a great expansion and specialization of amphibious 

 swamp-living forms, adapted to the marshy jungles then prevalent. 



These are the dinosaurs we know. Of the dry-land forms we know very little. A few Triassic types, possibly some of 

 the Jurassic ones, like Ornitholestes and HaMopus and Laosaurus, and the jungle-living carnivorous types departed less than 

 the others from the primitive dry-land type. The Sauropoda I regard as exclusively water-living — the larger forms at leasts 



a Proo. Am. Philos. Soc, vol. 43, p. 364, 1904. 



b Am. Jour. Sci., 3d ser., vol. 45, 1893, p. 142. 



e Am. Naturalist, vol. 38, Nov -Dec, 1904, p. 816. 



d Herein Matthew and Hatcher disagreed, as the latter considered the Sauropoda also as " terrestrial reptiles with amphibious habits, 

 passing much, perhaps most, of their time in shallow water, where they were able to wade about in search of food." The evidence is 

 strongly in favor of Matthew's belief.— R. S. L. 



