542 



HISTORICAL GEOLOGY 



tion of Brontosaurus (Fig. 506) or an allied form gives a truer 

 conception of the animal than any written description. The long 

 neck with its absurdly small head, the large body, stout limbs, and 

 long tail make an animal differing from any now living. Certain 

 characters of the skeleton are unusual. The leg bones, ribs, and tail 

 bones are solid and heavy; the head and the vertebrae of the neck and 

 back, on the contrary, being constructed so as to combine minimum 



Fig. 506. — Skeleton and restoration of Brontosaurus. These herbivorous dinosaurs 

 grew to be sixty feet long. (Model by C. R. Knight under the direction of Professor 

 Osborn. Copyright, American Museum of Natural History.) 



weight with the large surface necessary for the attachment of the 

 huge muscles. The significance of the remarkably heavy bones of 

 the lower portion of the skeleton, combined with the unusual lightness 

 in the upper portion, is that the animals lived in the water a large part 

 of the time. Under such conditions, the greater the. weight of the 

 bones, the greater would be the ease of walking with the body partly 

 submerged in water. The lightness of the head and the vertebrae of 

 the neck would be of advantage in making rapid movement of these 

 members possible. 



The teeth are long and either cylindrical or somewhat spoon-shaped 



