270 THE WORLD OF LIFE CHAP. 



Special Features in the Development of Vertebrates 



Another remarkable fact dwelt upon in Dr. Woodward's 

 address is the remarkably small brains of those early types 

 of vertebrates which were not destined to survive. The 

 most striking cases are those of the Mesozoic reptiles and 

 the Early Tertiary ungulate mammals, which both increased 

 to such an enormous bulk, yet retained throughout an 

 almost ludicrously small brain, as described in the last 

 chapter. The same was the case to a somewhat less extent 

 with the carnivorous mammals, the Creodonta and Sparas- 

 sodonta of the Early Tertiaries both of the eastern and 

 western hemispheres. These were sometimes as large as 

 lions or bears, and had equally well developed canine teeth, 

 but very small brains ; and they all died out in Eocene or 

 Early Miocene times, giving way to small ancestral forms of 

 our modern carnivores, which then increased in size and 

 developed larger brains, culminating in the highly intelligent 

 fox and dog, cat and leopard, of our own day. 



Yet another singular feature of some of the more highly 

 developed vertebrates is the partial or total loss of teeth. 

 This is well shown in the camels, which have only a pair of 

 incisors in the upper jaw ; while the whole vast family of 

 the deer, cattle, and sheep have a completely toothless pad 

 in the front of the upper jaws. This is apparently better 

 adapted for rapid browsing of grass and low herbage which 

 is stored up in the paunch for rumination when at rest ; 

 and the absence of teeth as a defence is compensated 

 by the possession of horns in a great variety of form and 

 structure. 



Even more remarkable is the total loss of teeth by 

 modern birds, although the early types of birds possessed 

 them. The bill, however, is often a very effective piercing 

 or tearing weapon ; and their strongly grasping claws and 

 hooked bill render the birds of prey almost as powerful and 

 destructive as the smaller members of the cat-tribe. This 

 partial or total disappearance of the teeth has no doubt been 

 helped on by the same principle which led to the persistent 

 increase of useless appendages till checked by natural selec- 

 tion or till it led to the extinction of the entire race. 



