Dinosaurs | Page 6

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.
[Illustration: 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.
[Illustration: 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.
ORDER SAURISCHIA Seeley. Suborder Coelurosauria von Huene (=Compsognatha Huxley, Symphypoda Cope.) Fam. Podokesaurid? Triassic, Connecticut. " Hallopodid? Jurassic, Colorado. " Coelurid? Jurassic and Comanchic, North America. " Compsognathid? Jurassic, Europe. Suborder Pachypodosauria von Huene. Fam. Anchisaurid? Triassic, North America and Europe. " Zanclodontid? } " Plateosaurid? } Triassic, Europe.* Suborder Theropoda Marsh (=Goniopoda Cope) Fam. Megalosaurid? Jurassic and Comanchic. " Deinodontid? Cretacic. " Ornithomimid? Cretacic, North America. Suborder Sauropoda Marsh (=Opisthocoelia Owen, Cetiosauria Seeley.) Fam. Cetiosaurid? } " Morosaurid? } Jurassic and Comanchic. " Diplodocid? } Order ORNITHISCHIA Seeley (=Orthopoda Cope, Predentata Marsh.) Suborder Ornithopoda Marsh (Iguanodontia Dollo) Fam. Nanosaurid? Jurassic, Colorado. " Camptosaurid? } " Iguanodontid? } Jurassic and Comanchic. " Trachodontid? (=Hadrosaurid?), Cretacic. Suborder Stegosauria Marsh. Fam. Scelidosaurid? } Jurassic and Comanchic. " Stegosaurid? } " Ankylosaurid? (=Nodosaurid?), Cretacic. Suborder Ceratopsia Marsh. Fam. Ceratopsid? Cretacic.
* Regarded by Dr. von Huene as ancestral respectively to the Theropoda and Sauropoda.
FOOTNOTES:
[Footnote 2: If some vast catastrophe should today blot out all the mammalian races including man, and the birds, but leave the lizards and other reptiles still surviving, with the lower animals and plants, we might well expect the lizards in the course of geologic periods to evolve into a great and varied land fauna like the Dinosaurs of the Mesozoic Era.]
[Footnote 3: The ancestral types have four complete toes, but in the true Theropoda the inner digit is reduced to a small incomplete remnant, its claw reversed and projecting at the back of the foot, as in birds.]
CHAPTER IV.
THE CARNIVOROUS DINOSAURS, ALLOSAURUS, TYRANNOSAURUS, ORNITHOLESTES, ETC.
SUB-ORDER THEROPODA.
The sharp teeth, compressed and serrated like a palaeolithic spear point, and the powerful sharp-pointed curved claws on the feet, prove the carnivorous habits of these dinosaurs. The well-finished joints, dense texture of the hollow bones and strongly marked muscle-scars indicate that they were active and powerful beasts of prey. They range from small slender animals up to the gigantic Tyrannosaurus equalling the modern elephant in bulk. They were half lizard, half bird in proportions, combining the head, the short neck and small fore limbs and long snaky tail of the lizard with the short, compact body, long powerful hind limbs and three-toed feet of the bird. The skin was probably either naked or covered with horny scales as in lizards and snakes; at all events it was