A NEWLY MOUNTED SKELETON OF THE ARMORED 

 DINOSAUR, STEGOSAURUS STENOPS, IN THE UNITED 

 STATES NATIONAL MUSEUM. 



By Charles W. Gilmore, 



Associate Curator of Paleontology, United states National Miiseuni. 



INTRODUCTION. 



The Stegosaurs were bj'^ reason of their large size, and ornate 

 dermal structure the more striking and characteristic of the large 

 reptilia that inhabited the northern hemisphere in Morrison time. It 

 should be said, however, that the family Stegosauridae is not con- 

 fined exclusively to North America, for specimens have been found 

 in England, France, and German East Africa that are but little 

 unlike the American representatives. At this time the origin of the 

 family is not known, though it is now generally believed that the 

 Stegosaurs had a bipedal ancestry, and that increasing bulk and 

 development of the dermal armor caused them to lose celerity of 

 movement, thus becoming sluggish, slow-moving quadrupedal crea- 

 tures of low mentality. 



By the measurement of the brain cavity in the skull of Stego- 

 saurus it is found that the brain displaces but 56 cubic centimeters 

 of water and has an estimated weight of about 2^ ounces. This small 

 organ directs the movements of a creature estimated to weigh several 

 tons, while the average normal human brain has a capacity of 900 

 cubic centimeters in a creature weighing from 130 to 150 pounds. 



The most remarkable feature of the nervous system of this great 

 brute, however, is the enormous enlargement of the spinal cord in 

 the sacral region, which i\as a mass of more than 20 times that of the 

 puny brain. At best the intelligence of this animal was of the lowest 

 order, hardly more than sufficient to direct the mere mechanical func- 

 tions of life. 



While the horned-dinosaurs, with skulls from 7 to 9 feet long, were 

 the largest headed land vertebrates the world has ever known, the 

 Stegosaurs are the smallest-headed when the great bulk of the body 

 is taken into consideration. The jaws are provided with a dentition, 

 made up of teeth so small and weak as to be always a source of won- 



Proceedings U. S. National Museum. Vol. 54— No. 2241. 



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