276 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



to North America, for specimens have been found in England, 

 France, and German East Africa that are but little unlike the 

 American representatives. 



Quite recently (1917) there has been placed on exhibition in the 

 musuem afc Washington the skeleton of one of these curious beasts, 

 shown here in plate 4, reproduced from a photograph. The skele- 

 ton as mounted measures 11 feet 9 inches in length, and stands 

 about 8 feet high from the ground to the top of the highest plate. 

 It was discovered in southeastern Wyoming — a region long famous 

 for the many and well-preserved fossil specimens found there. 

 Although collected more than 30 years ago it has only recently been 

 exhibited to the public. 



At present the origin of the family is not known, though it is now 

 generally believed that they were descended from 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 creatures of low mentality. By measurement of the 

 brain cavity in the skull of Stegosaurus it is found that the brain 

 displaces but 56 cubic centimeters of water, with an estimated weight 

 of about 2\ ounces. This small organ directed the movements of the 

 creatures, estimated to weigh several tons, whereas the average nor- 

 mal 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 has 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 

 functions of life. Whereas the great horned dinosaurs, with skulls 

 from 3 to 9 feet long, were the largest headed land animals 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 wonder and conjecture as to the real character 

 of their feeding habits. It would at least appear to indicate that 

 their food consisted of the most succulent of terrestrial plants. 



The structure of the large broad feet suggest they were land 

 haunting, doubtless of low swampy regions rather than the upland, 

 and such an environment would be most suitable for furnishing the 

 soft plant life necessary for their sustenance. 



In addition to the small head and the great difference in the propor- 

 tions of the fore and hind legs, the one most striking external fea- 

 ture of Stegosaurus is the ^unusual development of the skin armor, 

 consisting, as it does, of two parallel rows of erect alternating bony 



