Page:Popular Science Monthly Volume 66.djvu/148

144 to their duty of supporting their owner's weight, had to assume the grasping function as the hand relinquished it, and the claws became in consequence great talons, differing thus markedly from those of the earlier types.

One seems, therefore, justified in interpreting a second group of tracks, much larger than those of the Middletown slab, sharp clawed and with a very narrow sinuous tail trace, as having been made by a dinosaur of this group. If one should picture an animal about twenty feet in length, weighty in build, with talon-like hind claws, and therefore with small fore limbs and with a fairly erect posture so that the tip of the rather short heavy tail touched the ground, one would have a fair notion of this the maximum form, both in size and in degree of specialization of the Connecticut valley carnivores.

The other group of carnivorous dinosaurs were of a very different sort, always retaining their agility and the grasping power of their fore limbs, but not increasing very materially in bulk. A beautiful example of this race from the Jurassic beds of Wyoming has recently been mounted at the American Museum of Natural History, New York, and has been given the name of Ornitholestes, the bird robber, in allusion to its supposed habits. It is a slender animal with an extremely long tail. The hind limbs are fitted for locomotion par excellence, while the fore limbs are more slender with but three very long fingers in the hand, admirable for grasping elusive prey.

In studying the footprint slabs one frequently comes across some very small impressions, hardly exceeding three inches in length, three-toed, with no indication of a grasping claw behind, nor of a tail trace. One might be apt to attribute these little footprints to the young of the larger species until one notices the great interval between the successive tracks, a distance six to eight times the length of the foot itself. This of course gives evidence of extremely long limbs, so that the name of Grallator, he who walks upon stilts, which has been given to this group, is not inapt. While no skeletons are known from the same horizon with which the footprint may be compared, it seems safe to consider it one of these aberrant carnivores, of very slender build, agile, and of habits possibly similar to those of the wading birds.

It is but just to the earlier naturalists to say that we have no absolute proof that Grallator was not a true bird, but that it was seems doubtful, as the foot agrees in structure with that of known dinosaurs, and birds are totally unknown from so remote a period.

Plant feeding dinosaurs are known by their skeletal remains only from the Jurassic and Cretaceous periods, but that they existed during the earlier Triassic seems indubitably certain from the fact that their