Page:Popular Science Monthly Volume 34.djvu/489

Rh to the middle of the tail there was only one row of large scutes. At the end of the tail there were, as weapons of offense, several thick spines, about a foot long, so that a stroke of this tail must have been telling in its effects.



We have now made the acquaintance of several dinosaurs, yet they are by no means all the members of this numerous order, upon which already a whole literature has been published. Some of them are known only by their foot-prints. The Triassic sand-stone of the Connecticut Valley contains numerous impressions of five-, four-, and three-toed dinosaurs, which at first were considered as the foot-prints of large birds. They were made when these animals walked on the muddy shores of the Triassic ocean. The collections of Amherst and Yale College contain each several thousands of such impressions—a fact that gives some idea of the abundance of reptilian life on the continent at that time. Also, in Europe, we find that reptiles, and among them especially dinosaurs, are the most numerous and dominating class of the Mesozoic times—that is, during the Trias, Jura, and Cretaceous; so that these times are often called the age of reptiles. At the end of the Cretaceous period, however, the reptiles decreased, and the dinosaurs became entirely extinct—at least, we do not know of any Tertiary dinosaur, and none exists at present.

Our knowledge of these remarkable animals is a comparatively recent one; of them almost nothing was known thirty years ago, but since then discoveries have followed each other in rapid succession, and every year contributes new data. It is especially to three American scientists that we owe most of our knowledge about dinosaurs; they are Prof. Joseph Leidy and Prof. E. D. Cope, in Philadelphia, and Prof. O. C. Marsh, in New Haven.