Page:Popular Science Monthly Volume 66.djvu/147

Rh was a divergent one, the ultimate representatives differing widely from one another in bodily contour, form and structure of the teeth, and in mode of progression.

The earliest and most primitive of the carnivorous dinosaurs were those already alluded to as having been found at New Windsor and Springfield in the Connecticut valley. These creatures were somewhat lizard-like in general aspect, with the fore limbs fitted for grasping, while the much larger hind limbs, which were very bird-like, were used for locomotion. A study of the skeleton seems to indicate that the center of gravity came just about the region of the hip socket, so that the weight of the tail counterbalanced that of the forward portion of the body, thus making progression upon the hind limbs the only probable gait. The grasping hand, the structure of which is ill-fitted for locomotion, gives color to this assumption.

An extremely interesting slab in the Amherst College Museum, whose upper surface has been worn smooth by the feet of nearly two generations of men, for it did duty as a paving stone in the streets of Middletown, Connecticut, for more than fifty years, bears on its under surface in high relief numerous perfect tracks, in this instance not the footprints themselves, but the natural casts of the feet which made the prints, formed when the incoming tide deposited its load of sediment over the place where the creatures had walked. This bas relief, for such it may be called, admits of the following interpretation: that the makers of the tracks were true bipeds, as all of the casts are those of hind feet, moderately long of limb, walking with alternate steps, with compact bird-like feet, having three toes directed forward with moderately pointed claws, and evidently another directed backward whose claw only occasionally touched the ground. There is no sign of a caudal trace, showing that the tail if present was used only as a counterpoise. The size, length of limb, number and proportions of the toes, and the absence of hand and tail impressions, together with the fact that they are among the most numerous of the tracks, the makers of which would in consequence be among those most likely to be preserved as fossils, all point conclusively to the New Windsor dinosaur as the creature whose existence is thus recorded.

The carnivorous dinosaurs followed at least two lines of evolution, the more conservative of which simply increased in size and in consequent strength and ferocity throughout their racial career. In this group, perhaps the most remarkable feature is the constantly increasing disparity of size between the fore and hind limbs, for in the later forms the arms were so absurdly small that it is difficult to conjecture their use. As the fore limbs decreased in size, the hind legs, in