src="@public@vhost@g@gutenberg@html@files@19302@19302-h@images@fig007th.jpg" width="80%" alt="Fig. 7.: Skulls of Dinosaurs, illustrating the principal types Anchisaurus after Marsh, the others from American Museum specimens." tag="{http://www.w3.org/1999/xhtml}img"/>

Fig. 7.—Skulls of Dinosaurs, illustrating the principal types—Anchisaurus after Marsh, the others from American Museum specimens.

II. Amphibious Dinosaurs or Sauropoda. With blunt-pointed teeth and blunt claws, quadrupedal, with elephant-like limbs and feet, long neck and small head. Unarmored. Principal dinosaurs of this group in America are Brontosaurus, Diplodocus, Camarasaurus (Morosaurus) and Brachiosaurus, all of the Upper Jurassic and Comanchic periods.

III. Beaked Dinosaurs or Predentates. With a horny beak on the front of the jaw, cutting or grinding teeth behind it. All herbivorous, with pelvis of peculiar type, with hoofs instead of claws, and many genera heavily armored. Mostly three short toes on the hind foot, four or five on the fore foot. This group comprises animals of very different proportions as follows:

1. Iguanodonts. Bipedal, unarmored, with a single row of serrated cutting teeth, three-toed hind feet. Upper Jurassic, Comanchic and Cretacic. Camptosaurus is the best known American genus.

2. Trachodonts or Duck-billed Dinosaurs. Like the Iguanodonts but with numerous rows of small teeth set close together to form a grinding surface. Cretacic period. Trachodon, Hadrosaurus, Claosaurus, Saurolophus, Corythosaurus, etc.

3. Stegosaurs or Armored Dinosaurs. Quadrupedal dinosaurs with elephantine feet, short neck, small head, body and tail armored with massive bony plates and often with large bony spines. Teeth in a single row, like those of Iguanodonts. Stegosaurus of the Upper Jurassic, Ankylosaurus of the Upper Cretacic.

Fig. 8.—Hind Feet of Dinosaurs, to show the three chief types (Theropoda, Orthopoda, Sauropoda).

4. Ceratopsian or Horned Dinosaurs. Quadrupedal with elephantine feet, short neck, very large head enlarged by an enormous bony frill covering the neck, with a pair of horns over the eyes and a single horn in front. Teeth in a single row, but broadened out and adapted for grinding the food. No body armor. Triceratops is the best known type. Monoclonius, Ceratops, Torosaurus and Anchiceratops are also of this group. All from the Cretacic period.

Classification of Dinosaurs. It is probable that the Dinosaurs are not really a natural group or order of reptiles, although they have been generally so considered. The Carnivorous and Amphibious Dinosaurs in spite of their diverse appearance and habits, are rather nearly related, while the Beaked Dinosaurs form a group apart, and may be descendants of a different group of primitive reptiles. These relations are most clearly seen in the construction of the pelvis (see fig. 9). In the first two groups the pubis projects downward and forward as it does in the majority of reptiles, and the ilium is a high rounded plate; while in the others the pelvis is of a wholly different type, strongly suggesting the pelvis of birds.

Fig. 9.—Pelves of Dinosaurs illustrating the two chief types (Saurischia, Ornithischia) and their variations.

Recent researches upon Triassic dinosaurs, especially by the distinguished German savants, Friedrich von Huene, Otto Jaekel and the late Eberhard Fraas, and the discovery of more complete specimens of these animals, also clear up the true relationships of these primitive dinosaurs which have mostly been referred hitherto to the Theropoda or Megalosaurians. The following classification is somewhat more conservative than the arrangement recently proposed by von Huene.