Page:Popular Science Monthly Volume 34.djvu/484

 however, is not so great, and then let us transfer this into the reptilian system. For, while a kangaroo is a warm-blooded mammal, covered with hair, the dinosaurs were cold-blooded, scaly reptiles. The anatomy of the dinosaurs resembles that of the lizards and crocodiles, but in many respects it reminds us of the skeleton of birds. These bird-like features appear especially in the pelvis and the posterior legs, and are so striking that some scientists believe that birds are the descendants of dinosaurs; others think that birds and dinosaurs originated from a common ancestor. The close relationship of these two classes of animals will appear to us more plausible if we remember the fact that the birds of the Jurassic and Cretaceous periods resembled reptiles much more than they do now—for instance, in their possession of teeth. This may be said of dinosaurs in general, and we may now contemplate some of their known representatives.

If we enter the Museum of the Academy of Natural Sciences in Philadelphia, the first thing that attracts our eye is an enormous skeleton found at the left side of the entrance. It represents an animal seventeen feet high, and measuring from head to tail twenty-four feet. It is mounted so that it stands on its hind-legs and is supported by its strong and long tail, while the short anterior limbs rest upon a structure purporting to be a reproduction of a tree of past periods. If we examine the skeleton more closely, we find that only a few bones of the hind-legs and the tail are naturally found fossils, while all the other bones are artificial casts. But most of them are exact representations of the original fossil bones, which are kept under glass for the sake of better preservation. They were found in 1858 in the Cretaceous formation of New Jersey, and the animal has been described under the name of hadrosaurus. An exact imitation of this skeleton exists also in the National Museum at Washington.

The hadrosaurus is as yet the only complete mounted dinosaur in America, and it must not be forgotten that some parts of this skeleton were not found, but for the sake of completeness were formed in analogy to the others. In Europe they have been more fortunate in this respect. In the Royal Museum, at Brussels, in Belgium, there is the mounted skeleton of a similar dinosaur, the