140 



TEE AMERICAN MUSEUM JOURNAL 



skin of the horned dinosaurs, like that 

 of some modern lizards and of the duck- 

 billed dinosaurs, consisted of low po- 

 lygonal tubercles surrounding widely 

 separated, large, low, round tubercles. 

 Above the backbone,, especially in the 

 tail region, there was probably a row of 

 small plates, one above each vertebra. 



The horned dinosaurs lived during 

 the close of the Cretaceous period and 

 their remains are found from Texas 

 northward to southern Alberta. Sev- 

 eral genera are distinguished, chiefly 

 by characters of the skull which in all 

 forms was disproportionately large. In 

 some genera like the present Monoclo- 

 nius the nasal horn was long and the 

 horns above the eyes were short, while 

 in the last and largest of the race, Tri- 

 ceratops, the nasal horn was short and 

 the orbital horns extremely long. In 

 the genus Styracosaunis, also from the 

 Belly River rocks of Alberta, there was 

 a long nasal horn, and in addition 

 longer bristling spikes that radiated 

 from the border of the frill like a crown 

 similar to the spikes on the modern 

 lizard Phrynosoma, popularly known 

 as the "horned toad." 



Some writers have argued that the 

 horns were offensive and defensive 

 weapons, as on occasion they may well 



have been. A great variety of horn de- 

 velopment, however, is displayed in 

 different genera of similar habits, and 

 the horns and skull excrescences were 

 doubtless to a large extent ornamental, 

 as they are in many living lizards. 



The horned dinosaurs were huge bulky 

 fi'caturos and were probably sluggish of 

 habit, but tlic living animal weighed 

 much less than a mammal of equal size. 

 The skeleton, petrified, is very heavy, 

 whereas in life it was light, for the 

 bones are composed of highly cellular 

 tissue, while in the fossil state the 

 cavities are filled with silicates. 



These animals were land-living, vege- 

 table-feeding reptiles that lived along 

 the marshes of a sea which at that time 

 washed the eastern slope of the Rocky 

 Mountains. Their extinction was not 

 (hie to any great cataclysm nor on ac- 

 count of any sudden change in tem- 

 perature, for many plants that were 

 contemporaneous with them persisted 

 over the general region long after the 

 dinosaurs disappeared. As the moun- 

 tains were elevated this sea gradually 

 drained, cutting off their particular 

 kind of food, and as they were not 

 migratory creatures, the final disap- 

 pearance of the sea marked the end of 

 the dinosaurs in anv iriven loealitv. 



