No. 525] THE SAUROPODOUS DINOSAURS 



£59 



( H.viously a specialization of this kind will occur only 

 in an animal which habitually rests its weight on the 

 limbs, and it is necessary with increased weight, because 

 the increase of weight varies as the mass (cube of the 

 linear dimensions) while the increase in strength varies 

 as the cross section (square of the linear dimensions). 



This last circumstance will very clearly set a limit to 

 the size that an animal may attain as a practical working 

 mechanism. And here we are brought to face an un- 

 answerable difficulty if we consider the Sauropoda as 

 land animals. How is it that with their less perfect rep- 

 tilian organization of limbs and feet they were able to 

 attain so much larger size than has since been attained 

 by the land mammals with their more perfected organiza- 



<>t' u'iirantic land mammal- successively culminating and 

 disappearing, each a little larger than its predecessor, 

 each assuming the rectigrade limb as it approaches its 

 maximum size, the Proboscideans, the latest and largest 

 of all, and, so far as can be judged, the most perfect in 

 mechanical organization. But the Sauropoda, away back 

 in the Jurassic, far surpassed the largest elephants in 

 size ; and yet their joints are rough, imperfect, cartilage 

 covered, their muscular attachments imperfectly differ- 



tected mammalian organization permits, how is it possi- 



could so far exceed it? Ami if it is not. why have none 

 of the numerous gigantic Tertiary mammals exceeded 

 this size? 



If, indeed, we regard the Sauropoda as aquatic ani- 

 mals, adapted to wading, we solve this difficulty readily 

 enough, and find also an explanation for various pecul- 

 iarities in their construction which remain unexplained 



has the greater part of its weight buoyed up by the water, 

 and might attain a much larger size without transcending 



true fishes attain a much larger size than any land animal. 



