[Illustration: Plate 16.--Restoration Showing the General Appearance of Some of the Largest Animals Which Ever Trod the Earth. A mounted skeleton in the American Museum of Natural History is sixty-seven feet long, and the skeleton of a similar creature in the Carnegie Museum, Pittsburgh, is eighty-seven feet long. They lived millions of years ago during the middle and late Mesozoic era. (_After C. R. Knight. Courtesy of the American Museum of Natural History, New York._)] The most remarkable walking reptiles of all time were the dinosaurs or "terrible lizards." We shall describe enough types of these unique creatures to give the reader a fair idea of their appearance and habits. Most astonishing of all were the sauropods including the largest animals which ever trod the earth. They grew to be as much as sixty to ninety feet or more in length. Remarkably well preserved skeletons have been found, one from Utah, eighty-seven feet long, being mounted in the Carnegie Museum of Pittsburgh. The largest of these brutes stood fifteen to twenty feet high and they must have weighed thirty to fifty tons. The very long, serpentlike neck and tail, and very small head were grotesque features. Considering the structure of the dinosaurs, the kind of strata in which they are embedded, and the associated fossil remains, it seems clear that they mostly lived in and near fresh water and on near-by lowlands. The character of their teeth shows that they fed entirely on soft plants which they must have habitually bolted because their teeth were not well adapted to grinding food. It is difficult to believe that a single huge beast could have consumed less than a few hundred pounds of vegetable matter per day, and, on account of the very small size of the head, he must have spent most of his time eating. Also the comparatively very small size of the brain, and its simplicity of structure, render it certain that they were extremely stupid creatures. "To make up for this they had an enormous enlargement of the spinal cord in the sacral region (i.e., over the hind legs). This sacral brain--if we may so call it--was ten to twenty times bigger than the cranial brain. It was necessary in order to work the powerful hind legs and tail." (Le Conte.) [Illustration: Fig. 60.--Skeleton of a great four-legged (sauropod) dinosaur. A mounted skeleton in the American Museum of Natural History, New York, is sixty-seven feet long. This creature lived millions of years ago during the Jurassic period. (After Marsh.)]