A knowledge of the form of the appendages to the trunk of animals is of great service to the geologist, for it has been well and truly said, that the organic remains imbedded in rocks are as medals struck in commemoration of the great revolutions which the earth has undergone, and so small a portion as the extremity of an animal is sufficient to indicate its nature, and to enable us to ascertain the class and order to which it belongs. Let us take a few examples. Some fossil bones were discovered by General Washington near his seat in Virginia. Mr. Jefferson, by whom they were examined, stated that they had belonged to an enormous carnivorous animal, which from the size of its claws he named the Megalonyx. Upon an examination more carefully conducted by Cuvier, it was found that in the paw the second bone of the toe was symmetrical, while in animal feeders furnished with retractile claws it is curved, and not symmetrical; the first bone, too, was the shortest, whereas in the lion and others of the feline tribe it is the longest. Whence Cuvier was led to conclude that the creature in question was a sloth of large dimensions, which fed only upon plants.
Upon another occasion, from a careful consideration of the form and size of a toe found in the Palatinate, near Eppelsheim, Cuvier was able to determine that the animal to which it belonged was of the edentate tribe of Pangolins. It was from an examination of the hand that Cuvier decided upon the nature of the Pterodactylus. This curious animal partook of the nature of both the reptile and the bird. Like the bird, it was furnished with a long neck and a horny beak, but in its jaws and teeth it resembled the crocodile. It had not, however, like the bird, feathered wings without fingers to strengthen them, nor had it a wing in which the thumb alone is free, like that of the bat. Instead of the bony pieces of all the fingers being equally prolonged, the second finger only was extended to a great length, and from it the wing spread out, the other fingers being short and furnished with nails like the toes of ordinary animals. Collini, its discoverer, supposed it to be of marine origin; Soemmerring contended that it was a mammal; but its true place in the animal series was first assigned to it by Cuvier, who has satisfactorily shewn that it is in fact intermediate between a bird and a reptile.
A knowledge of the form of the extremities of animals has been of great service to palæontology in another way—in proving the existence of certain species of animals at given periods of the earth’s formation, from the print of their footsteps left upon the sand or other material of the strata while it was yet in a soft state. Such traces were first observed by Dr. Duncan in Dumfries-shire. On examining a sandstone quarry, he found these prints not on one only, but on several successive layers of the stone; so that they must have been made at periods distant from each other. Similar impressions have been since observed in the Forest marble-beds near Bath, at Hessburg in Saxony, in the State of Connecticut, and in some other parts of the world.
“The marks found in Dumfries-shire, of which there were as many as twenty-four upon a single slab, formed as it were a regular track, with six distinct repetitions of each foot, the fore and hind feet having left different impressions, and even the marks of the claws being discernible. They appear to have been made by some animal of the tortoise kind. At Hessburg the impressions were discovered in quarries of grey and red sandstone alternating; and the marks were both larger and more distinct than those found in Scotland. In one the hind foot measured twelve inches in length, and the fore foot always appeared much smaller than the hind. From this circumstance, and from the distance between the two being only fourteen inches, it is conjectured that the animal was a marsupial like the kangaroo, and it has been termed by Dr. Kaup Chirotherium, from the supposed resemblance of the four toes and turned-out thumb to a hand. In the State of Connecticut, near Northampton, footsteps differing exceedingly in size have been found in inclined strata of sandstone. They were evidently made before it assumed its present position. The marks are always in pairs, and the tracts cross each other like those of ducks on the margin of a muddy pond. One is of the length of fifteen or sixteen inches, and a feathery spur or appendage appears to have been attached to the heel, eight or nine inches long. The distance between the steps is proportioned to their length, but in every case the pace appears to have been longer than that of the existing species of birds to which they approach nearest—the ostrich, and the animal must consequently have been proportionably larger. How much larger he was than the ostrich may be gathered from this, that the large African ostrich has only a foot ten inches long, less than two-thirds that of this bird, and yet stands nine feet high. These proportions would give a height of fourteen feet to the extinct animal.”[4]
The characters afforded by the foot have recently enabled Mr. Strickland to determine that the dodo, a bird now extinct, is not related either to the gallinaceous birds,—the vulture or the ostriches as some have conjectured,—but is closely allied to the pigeons.
From this cursory examination of the animal world we may gather the important conclusion, that from the structure of an extremity we may obtain a complete insight into the entire organisation of an animal; and thus the paws furnished with sharp retractile claws of the lion indicate at once to a naturalist its strong teeth, its powerful jaws, and its muscular strength of limb; while from the cleft foot of the cow, the complicated structure of its stomach, the definite peculiarities of its jaws, and its vegetable diet, may with equal certainty be predicated.
Thus, as Paley justly observes, “In the swan, the web foot, the spoon bill, the long neck, the thick down, the graminivorous stomach, have all a relation to one another, inasmuch as they all concur in one design, that of supplying the occasions of an aquatic fowl, floating upon the surface of shallow parts of water, and seeking its food at the bottom. Begin with any one of these peculiarities of structure, and observe how the rest follow it. The web foot qualifies the bird for swimming, the spoon bill enables it to graze. But how is an animal, floating upon the surface of pools of water, to gaze at the bottom except by the mediation of a long neck? And a long neck is accordingly given to it. Again, a warm-blooded animal, which was to pass its life upon water, required a defence against the coldness of that element. Such a defence is furnished to the swan in the muff in which its body is wrapped. But all this outward apparatus would have been in vain if the intestinal system had not been suited to the digestion of vegetable substances.”[5]
And, again, of the mole: “The form of the feet fixes the character of the animal. They are so many shovels; they determine its action to that of rooting in the ground; and every thing about its body agrees with this destination. The cylindrical figure of the mole, as well as the compactness of its form, arising from the terseness of its limbs, proportionally lessens its labour; because, according to its bulk, it thereby requires the least possible quantity of earth to be removed for its progress. It has nearly the same structure of the face and jaws as a swine, and the same office for them. The nose is sharp, slender, tendinous, strong; with a pair of nerves going down to the end of it. The plush covering, which, by the smoothness, closeness, and polish of the short piles that compose it, rejects the adhesion of almost every species of earth, defends the animal from cold and wet, and from the impediment which it would experience by the mould sticking to its body. From soils of all kind the little pioneer comes forth bright and clean. Inhabiting dirt, it is of all animals the neatest.”