CAUSES OF EXTINCTION. 195 



The stegosaurs, claosaurs, and ceratopsians may have been more or less land haunting, but not upland, and they all 

 impress me as amphibious adapt ations/rom a type highly specialized for land locomotion. 



In the later Cretaceous the terrestrial province was greatly expanded by the development 

 of the upland flora which provided for a corresponding spread of terrestrial types. These were 

 derived mainly from the previous^ arboreal mammals, the birds maintaining their aerial 

 habitat, while of the reptiles, the lizards and snakes only were able to adapt themselves to these 

 new conditions. At the time of the expansion of the upland realm there was great dwindling of 

 the amphibious-aquatic province, due to the orogenic movements occurring at the close of the 

 Mesozoic, which drained the Cretaceous sea and its adjacent swamps and river deltas and 

 caused the Reptilia to undergo a corresponding diminution. 



PROBABLE CAUSES OF EXTINCTION. 



Several theories have been advanced as to the probable causes of extinction of the Ceratopsia, 

 some authors maintaining that the horned herbivorous types were in part destroyed by the 

 large carnivorous dinosaurs. There is always, however, a balance in nature, an offsetting of 

 Carnivora or parasitic forms against their plant-feeding contemporaries and, though the latter 

 may have been held in check by the former, it is extremely improbable that strictly contem- 

 poraneous forms which' have evolved in the same environment could ever exterminate one 

 another. It seems that animals of another race, or hordes of creatures which emigrated from 

 another region, would be more likely to exterminate their predecessors. The mammals fulfill 

 the requirements of a new foe, and the development of the frill in the Ceratopsia has been consid- 

 ered as meeting the necessity for a better protection of the neck blood vessels from the weasel-like 

 attack of small but bloodthirsty quadrupeds. Another notion advanced by Morris and ampli- 

 fied by Cope was that the Cretaceous mammals sought out the eggs of the dinosaurs and 

 destroyed them — Cope even going so far as to suggest the Multituberculata, with their long, 

 sharp anterior teeth, as the probable offenders. 



Matthew, however, has given the Mesozoic Mammalia a totally different habitat from that 

 of their dinosaurian contemporaries in the belief recently expressed that the mammals were 

 distinctively arboreal, while we are led to believe that all dinosaurs were either terrestrial or' 

 possibly amphibious, the Ceratopsia at least inhabiting the lowlands in a swamp or delta 

 region. 



By far the most reasonable cause, and the one which Hatcher himself believed, seems to be 

 that of changing climatic conditions and a contracting and draining of the swamp and delta 

 regions caused by the orographic upheavals which occurred toward the close of the Cretaceous. 

 The Ceratopsidse and their nearest allies, the Trachodontida?, both highly specialized plant 

 feeders, were unable to adapt themselves to a profoundly changed environment because of this 

 very specialization, and, as a consequence, perished. 



That the Ceratopsia made a gallant struggle for survival seems evident, for they lived 

 through the first series of upheavals at the close of the Laramie and also the second series at the 

 close of the Arapahoe, which were accompanied by great volcanic outbursts in the Colorado 

 region; but the changes accompanying the final upheavals which formed most of the great 

 western mountain chains and closed the Mesozoic era gave the death blow to this remarkable 

 race. 



