382 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



he should have been misled by their resemblance to the horn cores 

 of some of the extinct buffaloes. 



It appears that certain teeth and bones found first by Dr. F. V. 

 Hayden on one of his expeditions to the West as early as 1855, and 

 later discoveries by Prof. E. D. Cope in 1873 and 1876 were also 

 ceratopsian reptiles, but the fragmentary parts found by the Phila- 

 delphia professor gave him no idea of what the creatures were like, 

 though with his usual perception he recognized that they differed 

 from any animals then known to science, and they were given the 

 names Agathaumas and Monodonius. 



These were the first of a long series of discoveries leading down to 

 the present day, which through scientific and popular descriptions 

 have made the horned dinosaurs familiar to the world at large. 



There are a great many different kinds of these horned dinosaurs. 

 Most of them are known from skulls or parts of skulls, for the com- 

 plete skeletal structure has been found only in the genus Monodo- 

 nius, and of their evolution and early history we know comparatively 

 little as yet. 



The most striking feature of the horned dinosaurs is the gigantic 

 head armed with horns and a great bony crest or frill that pro- 

 jects backward over the neck. In Tricerat&ps, the last of the race, the 

 skull with its projecting frill sometimes attains a length of 8 feet in 

 old individuals, with a pair of large horns that extend upward and 

 forward from above the eyes, and a smaller horn on the nose. In 

 Monodonius, a geologically older genus, these horn conditions are 

 exactly opposite, the single horn on the nose being the larger, the 

 brow horns being short and rudimentary, the frill being pierced by 

 large openings or " fenestra," as they are called. The examples men- 

 tioned represent in a way the two extremes for between them lie other 

 genera intermediate in size and in the development of their horn 

 cores and frill. There are small-horned and large-horned animals, 

 some that have horns curving forward, others that bend backward, 

 others that turn outward, and still others that stand erect. At this 

 time we do not know whether these horns were found only on the 

 males or whether they are the marks of distinct species. 



Space permits the mention of only a few of the striking forms, for 

 it is beyond the scope of the present article to describe all of the 

 various kinds. 



That the horned dinosaurs were fighters and often engaged in com- 

 bat is shown by the healed wounds that are found in many skulls, 

 broken horns, fractured and healed jaws, and pierced frills. A pair 

 of horn cores of Triceratops in the National Museum bear witness to 

 such an encounter ; that the right horn was broken off in life is evi- 

 dent from the fact that the stump has rounded over and healed while 

 the size of the other shows the animal to have reached a good old age. 



