3i6 POPULAR SCIENCE MONTHLY. 



of years, some of them at least, because of their comparative insignifi- 

 cauee among their many powerful relatives. Of these relatives, the huge 

 dinosaurs, the swimming iehthyosaurs, plesiosaurs and mosasaurs, and 

 the flying ornithosaurs, with others scarcely less renowned in geological 

 history, are known only from the scanty records of the rocks. 



Of all the reptiles of the past, perhaps the most extraordinary, the 

 ones which departed most from the reptilian type in form and habits, as 

 well as the most highly specialized of all cold-blooded animals of the 

 past or present, were the ornithosaurs or pterodactyls. They made tlieir 

 appearance in geological history, so far as is known, suddenly and in a 

 highly developed state; we know nothing of their antecedents, nor in- 

 deed of their descendants. They flourished through millions of years 

 in great numbers and multitudinous forms, and then, evidently, as sud- 

 denly disappeared. So different were these flying creatures from any 

 others of the past or present that their proper place in the animal king- 

 dom has been disputed. They were at flrst thought to be birds, and so 

 described; and this idea of their relationship found expression in the 

 name by which they are more properly known, the ornithosaurs or bird- 

 reptiles. Some authorities would even yet give them a place all their 

 own among animals, coordinate with the birds and reptiles. But they 

 are now so well known to students of extinct life, and in so many 

 forms, that there can scarcely be longer a serious question of their 

 real, though highly modified, reptilian affinities. It is not impossible, 

 however, though somewhat improbable, that they were, unlike others 

 of their class, warm-blooded animals ; it is at least highly probable that 

 their circulatory and respiratory systems reached a much higher degree 

 of perfection than is the case in any cold-blooded animals of the present 

 time. 



Restoration of Pteranodon (Ornithostoma). Expanse of Wings, Nineteen Feet, Six 



Inches. 



As flying organisms they attained the highest degree of specialization 

 that has ever been reached among animals with a back-bone, at least so 

 far as their skeleton was concerned. Some of them, indeed, seem to 

 have nearly lost all other powers of locomotion — they could move 

 through the air only. Furthermore, the relative proportion between 

 volant surface and bodj^-weight in some of these pterodactyls has been 



