(Monoclonius nasicornus )
Skeleton restored from bones found in the Red Deer River region, Canada. (American Museum of Natural History)

Dinosaurs—Ancestors of Birds

No class of the extinct reptiles is so familiar, by name at least, as is that of the dinosaurs, mainly because of the enormous size of some of them, and the fact that their prodigious skeletons are exhibited complete in many museums. No other land animals ever approached some of them in bulk. A great number of species have been exhumed, yet as a group these reptiles are only imperfectly known, for the fossils are not scattered throughout the whole extent of Mesozoic deposits, but only in two limited periods of that era separated by two or three millions of years. All of them had short, compact bodies, long tails, and long legs for a reptile, and instead of crawling they walked or ran, sometimes upon all fours, more generally on the hind limbs, like ostriches. They ranged in size from that of a cat to the prodigious bulk of the diplodocus or the brontosaurus, seventy feet long and perhaps twenty feet high at the hips, while an East African species appears to have been even far bigger. Some were herbivorous, and dwellers mainly in marshes and swamps; others ranged the uplands, armored for defense against huge predatory kinds, and still others had horny beaks like birds. It is believed, in fact, that our birds are descended from the same stock as these creatures, through an early offshoot.

(American Museum of Natural History)