Page:Popular Science Monthly Volume 66.djvu/150

146 wide variation and distribution in the Jurassic implies an ancestry in the earlier period, and also that their footprints on the Triassic sandstones are unmistakable.

The more primitive herbivores resemble their carnivorous allies in general contour and in mode of progression, though differing in certain internal characters and in the teeth, these being necessarily changed to enable their owner to chop or grind up the plants upon which it lived. The rear part of the jaws became, in the later forms, veritable magazines of teeth, the latter replacing one another in vertical succession,

a new one being always ready to take the place of one lost or worn out in service. The front part of the mouth bore a few teeth in the earlier types, but these soon gave way to a horny upper and lower beak, turtle-like in aspect, probably used for cropping succulent herbage.

The hind feet were still very bird-like, especially in the less specialized forms, but with blunted claws, while the hand always retained its five fingered condition with short rounded nails. The fore limbs could always be used for the support of the forward parts of the body, though perhaps not always for food gathering. It is extremely doubtful whether any of the earlier plant feeders ever walked on all fours, though in the later forms, owing to the great weight of armament which they carried, a four-footed gait was rendered necessary. The herbivorous dinosaurs proved a more plastic race than their carnivorous brethren, and towards the close of their career there arose among them the remarkable types, already alluded to, which marked the decadence of the group.

In the footprint fauna the herbivores were all true bipeds, but did occasionally impress the hand, including thus all the footprints of the second or occasionally quadrupedal group, and probably some of the first as well, though this is open to question.

The footprints give us thus our first recorded evidence of herbivorous dinosaurs in the Triassic, which will some day probably be verified by the finding of their bones.