Some of the more notable genera were: Anchisaurus, a primitive carnivorous dino saur, some seven feet in length, from the Upper Triassic, known from several skeletons and numerous footprints from the Connecticut Val ley and from New Jersey. See Fig. 1.
Allosaurus, a splendid type, with a length of 34 feet, more than half of which was included in the slender tail. This creature is from the Comanchian or Lower Cretaceous of Wyoming and the adjacent West and is represented in the Old World by a near ally, Megalosaurus, of wide distribution, both in time and space.
Tyrannosaurus, the terminal member of the race, 47 feet long, with the bodily bulk of an elephant, a great four-foot head, armed with teeth three to six inches in length, carried 20 feet in the air, relatively tiny hands, but huge feet which bore powerful claws. This creature, which has been most appropriately named, was the most appalling devourer of flesh which ever stalked abroad, but while admirably adapted and equipped to meet and overcome the unwieldy herbivores of its day, would find it difficult to make a living in these days of brainier, more agile mammals. See Fig. 2.
Accompanying their larger, fiercer kin in their evolutionary career were the smaller and more active carnivores, beginning with the slender Podokesaurus of t'he Triassic and with Compsognathus of the Jurassic, the smallest known dinosaur, and culminating in the tooth less forms which we have mentioned. Their increase in size was gradual, and their slender ness and well developed grasping hands imply, except in the last mentioned, their adaptation to more agile and feebler prey.
relatively race were the amphibious dinosaurs or Sauro poda, apparently derived from the theropod group, but departing widely in habitus and con sequent habit. What gave them their evolu tionary trend we do not know, but their one distinctive character was a vastly increased bulk, which necessitated their forsaking the strictly terrestrial habitat and becoming partly if not wholly water-borne. This increasing bulk also rendered bipedality impossible, and if they were ever really capable of walking exclusively on the hind limbs, they soon lost that power except, perhaps, when in the water; indeed, in certain of the later types a large part of the weight was borne on the fore limbs, which, con trary to dinosaurian custom, actually exceeded the hinder members in length and bulk. As a
further consequence of their increasing stature and amphibious habitat, the neck grew very long so that the small head might range• through a considerable arc, both horizontally and verti cally, in its search for food.
The exact nature of this food we do not know, but the spoon- or pencil-shaped teeth, somewhat worn at the end, are in the front of the mouth as with the true carnivores, and could neither have been used for the rending of flesh nor for the mastication of plant food. The inference is that the dietary was vegetal — pos sibly some floating or readily dislodged aquatic plant which grew in great abundance, like the water hyacinth of the Nile. This must have been drawn into the stomach in great inert masses, where a powerful muscular device like a gizzard, together with swallowed stones such as have been actually found between the ribs of certain specimens, aided in their digestion.
These creatures waded, as their heavily ballasted limbs imply, or swam where depth re quired it, but show no distinctively natatory adaptation. They were apparently unarmored, and weaponless, unless the terminal 10 feet of the tail, which was sometimes slender like a whiplash, might be interpreted as a weapon. The earliest forms were moderate in size, some 40 feet perhaps, but the later types were gigantic, the longest authentic measurement being 87 feet, while the living weight exceeded 35 tons. Their bulk, but probably not their length, has been exceeded by the modern whales, but this is because of the slender neck and tail of the dinosaur as compared with the large head borne directly on a neckless trunk and the powerful propelling tail of the cetacean.
Some of the more notable Sauropoda were: Brontosaurus, (Fig. 3) 65 feet long and heavily built, from the Comanchian of Colorado to South Dakota; Diplodocus, a contemporary, 87 feet in length and much slenderer in build, from Wyoming and Colorado; and Brachiosaurus, some 80 feet in length, the most ponderous of all, with huge neck and fore limbs, a giraffe-like wader found in rocks of equivalent age in Wyoming and at Tcnda guru, East Afnca.