824 R. S. LULL SAT ROPODA AND STEGOSAFRTA OF THE MORRISON 



Saiiropod;!, oji tlic other liaml, and especially the armored dinosaurs, 

 which are highly specializetl ty|)('s, arc hori/on markers of importance. 



Sauroi'()J)A 



The Sauropod diiiosaiii's include some (d' the greatest of the worliTs 

 creatures, exceeded in size only hy the largest of existing whales. The 

 huge size, while in itself a high specialization, can only he attained l)y 

 members of a relatixely primitive stock. Thus we see in the attainment 

 of size the de\ elopment of remarkable specialization on' the part of skele- 

 tal detail, vet in the main plan of structure the Sauropoda were among 

 the most generalized of dinosaurs. 



They were (piadiupedal reptiles, with a huge, relatively short body, 

 borne on massive, pillar-like limbs which still retained the archaic num- 

 ber of five digits in fore and hind foot, although the outermost ones were 

 in process of reduction. The neck and tail were of great length, while 

 the head, with its battery of prehensile teeth in the forward portion of 

 the mouth, was very small for so huge a beast, having a diameter less 

 than the average of the neck which bore it. The limb bones were exceed- 

 ingly heavy, long, and straight, with highly rugose ends, as though the 

 articulation betAveen them was in large measure cartilaginous. The ver- 

 tebral column, on the other hand, is a marvel of lightness, and from the 

 standpoint of strength, combined with rigid economy of material, is per- 

 haps the most remarkable piece of nature's engineering known. The 

 size, lightness of the vertebral column, especially of the neck, the com- 

 pressed and powerful tail, the incomplete articulations of the limbs, such 

 as are never found in terrestrial animals today, and the position of the 

 external nostrils on the top. of the head all point to an amiDhibious if 

 not an exclusively aquatic habitat. The weight of the limbs would serve 

 as ballast to permit the animal to wade in relatively deep water, while 

 the tail would be very effective for more active locomotion through the 

 water in case of need. 



The feebleness of the dentition on the part of some genera at least has 

 given rise to considerable argument as to the food of these creatures. 

 All are pretty well agreed, however, that some luxuriant and nutritious 

 aquatic plants which could be loosened l)y the sharp claws or by the rake- 

 like teeth and then swallowed down in Jiuge quantities, without mastica- 

 tion, would best subserve the creatures' need. 



The habitat of the Sauropoda may best be visualized by imagining 

 conditions such as now" exist in tropical America, more especially over 

 the coastal plain of the lower Amazon : low-lying lands, but little above 



