. Elements of geology : a text-book for colleges and for the general reader. Geology. 440 MESOZOIC ERA—AGE OF REPTILES. of them walked habitually on their hind-legs alone, in the manner of birds. (3.) Like birds and some mammals, many Dinosaurs tread on their toes (digitigrade) and not like reptiles on the whole foot (planti- grade). (4.) Like birds, also, many—but not all—had only three func- tional toes, and therefore made tridactyle tracks; and even the number of toe-joints follows the order of those of birds—i. e., there were three in the inner toe, four in the middle, and five in the oute
. Elements of geology : a text-book for colleges and for the general reader. Geology. 440 MESOZOIC ERA—AGE OF REPTILES. of them walked habitually on their hind-legs alone, in the manner of birds. (3.) Like birds and some mammals, many Dinosaurs tread on their toes (digitigrade) and not like reptiles on the whole foot (planti- grade). (4.) Like birds, also, many—but not all—had only three func- tional toes, and therefore made tridactyle tracks; and even the number of toe-joints follows the order of those of birds—i. e., there were three in the inner toe, four in the middle, and five in the outer toe. (5.) Still more curious is the resemblance to birds, in the structure of the. Fig. 691.— A, Dromseus; B, Dinosaur; C, Crocodile: As, astragulus; Ca, calcaneum, ankle-joint. In reptiles—as also in mammals—the joint is between the shank-bones and the tarsus ; in birds, the astragalus and calca- neum are consolidated with the shank, and the motion is below these bones of the tarsus. Some Dinosaurs are like birds in this regard. Fig. 691, ABC, illustrates this point. (6). Many Dinosaurs pos- sessed a clavicle—a bone found in all birds and many mammals, but no living reptile. We shall very briefly describe only the most re- markable. The Iguanodon was one of the best known as well as one of the largest. It was a huge herbivorous Dinosaur, found in the Upper Jurassic and Lower Cretaceous of Europe. It takes its name from the resemblance of its teeth (Fig. 692) to those of an Iguana—a living herbivorous reptile, about four or five feet long, although in other respects there is little affinity. Until recently, only portions of the skeleton were found; but the enormous size of these indicated an ani- mal at least thirty feet long, and several times the weight of an ele-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly re
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
