194 DINOSAURS OF NORTH AMERICA. 



of a predentary bone, and the well developed postpubis, are important 

 characters that point to the Ormthopoda as near allies, with a common 

 ancestry. These positive characters are supplemented by some points 

 in the structure of the skull and the form of the teeth. 



There are, however, a large number of characters in which the Stego- 

 sauria differ from the Ornithopoda, and among these are the following: 



(1) All the bones of the skeleton are solid. 



(2) The vertebrae are all biconcave. 



(3) All the known forms have a strong dermal armor. 



(4) The second row of carpals and tarsals are unossified. 

 {5) The astragalus is coossified with the tibia. 



(6) The spinal cord was greatly enlarged in the sacral region. 



RESTORATION OF STEGOSAURUS. 

 Plate LII. 



In this restoration the animal is represented as walking, and the 

 position is adapted to that motion. The head and neck, the massive 

 fore limbs, and, in fact, the whole skeleton, indicate slow locomotion 

 on all four feet. The longer hind limbs and the powerful tail show, 

 however, that the animal could thus support itself, as on a tripod, and 

 this position could perhaps have been easily assumed in consequence of 

 the massive hind quarters. 



In the restoration as here presented the dermal armor is the most 

 strikiug feature, but the skeleton is almost as remarkable, and its high 

 specialization was evidently acquired gradually as the armor itself 

 was developed. Without the latter many points in the skeleton would 

 be inexplicable, and there are still a number that need explanation. 



The small, elongated head was covered m front by a horny beak. 

 The teeth are confined to the maxillary and dentary bones, and are not 

 visible in the figure here given. They are quite small, with compressed, 

 fluted crowns, and indicate that the food of this animal was soft, suc- 

 culent vegetation. The vertebnv are solid, and the articular faces of 

 the centra are biconcave or nearly flat. The ribs of the trunk are 

 massive and placed high above the centra, only the tubercle being 

 supported on the elevated diapophysis. The neural spines, especially 

 those of the sacrum and anterior caudals, have their summits expanded 

 to aid in supporting the massive dermal armor above them. The limb 

 bones are solid, and this is true of every other part of the skeleton. 

 The feet were short and massive, and the terminal phalanges of the 

 functional toes were covered by strong hoofs. There were five well- 

 developed digits in the fore foot, and only three in the hind foot, the 

 first toe being rudimentary and the fifth eutirely wanting. 



In life the animal was protected by a powerful dermal armor, which 

 served both for defense and offense. The throat was covered by a thick 

 skin, in which were embedded a large number of rounded ossicles, as 

 shown in the plate. The gular portion represented was found beneath 



