5 66 POPULAR SCIENCE MONTHLY 



Fig. 11. Restoration of the Skeleton of Diadectes. 



ing to the ribs in number and extending down over the sides in broad 

 curves so that the animal was completely closed in a bony cuirass. Add 

 to this that the top of the head was heavy and solid, and we can imagine 

 that the animal when it crouched close to the ground, with its head 

 drawn down and in, resembled very closely the modern Armadillo in 

 its attitude of defense and was able to resist the attack of even the long- 

 tusked Dimetrodon. 



This donning of armor is one of the striking things about the 

 animals of the Permian age ; it occurred among the amphibians as well 

 as among the reptiles and is closely correlated with the development 

 of great tusks in the predatory forms. As the armor-piercing weapons 

 grew ever stronger the armor grew ever heavier and more completely 

 adapted to the body. The same thing has happened once and again 

 in the world's history; much later, in Tertiary time, when the world 

 was thirty millions of years older, we have a repetition of the same 

 thing. The great saber-toothed tiger developed canine tusks six inches 

 in length, and the small edentates, the natural prey of the tiger, de- 

 veloped first small isolated bones in the skin, but ever as the tusks grew 

 the bones in the skin became larger and better arranged, until the 

 almost perfect protection of the Armadillo appeared. It was the 

 prophecy of modern warfare between armor-piercing shells and armor 

 plate, we have not seen the end in human history, but in the old days 

 it continued to the practical extinction of both parties to the contest. 

 Perhaps there is a neglected object-lesson here. 



Turning from the reptiles to the amphibians, we find a no less 

 wonderful group of animals. During the preceding age, the Car- 

 boniferous, the amphibians had been masters of the world; by the 

 Permian, their time of dominance was past and they were already on 

 the downward path that was to end in the obscure toads, frogs and 

 salamanders of our meadows. But they were far from yielding tamely 

 to their fate; they developed in all possible directions in a seemingly 

 frantic effort to regain their lost dominance. During the Permian 

 and the succeeding Triassic ages, there lived some of the largest 

 amphibians the world has ever seen; they betook themselves to the 

 water and developed eel-like bodies; they lived in hollow trees, as 

 witness the discoveries of Sir Wm. Dawson in the stumps of trees 



