Part 4

The foot is divided into four toes; the two outer of which seem to be connected by a common basis. The inner toe has three phalanges; the second toe, also three; the third and fourth toes, four each. The first is the shortest, the second longer, the third longest, the fourth shorter than the third. It will appear, then, that this track differs from that of birds in the number of toes pointing forwards; these being four, while in birds the forward toes are only three. There is a difference also in the number and arrangement of the articulations.

The track in our possession is twenty inches long by thirteen and a half inches broad. The rock in which it is imbedded is a dark-colored sandstone. President Hitchcock has a slab showing a regular series of tracks of this animal; the distance between the steps being about three feet, and the tracks equidistant and alternate, which would not be the case if the animal had been quadrupedal. In a quadruped, the horse for example, the hind feet are set down near the fore feet, and sometimes even strike them. Hence it must be inferred that the track in question was that of a biped, or of a quadruped which did not use its fore feet in progression, like a kangaroo. We naturally ask, What kind of biped could this have been? Evidently not a man, the size of the foot being too large to admit such a supposition; nor could it have been a bird, the number of toes and their direction not admitting this hypothesis.

Tetradactylous birds, or those which have four toes, have only three of them directed forwards, and the fourth backwards, generally. There are, however, exceptions; some birds have four toes directed forwards: this is the fact with the Hirundo Cypselus and the Pelicanus Aquilus of Linnaeus, or Man-of-war Bird. But the articulations are different in the two animals, birds having regularly two, three, four, and five phalanges, and the spur, where it exists, supported by a single osseous phalanx; whereas the Otozoum has three phalanges in the inner and second toe, four in the third and fourth toes. In this last arrangement, the Otozoum is decidedly different from all known birds. It is not likely to have been a tortoise or a lizard. The kangaroo has four feet, and uses only two in progression, moving forward by leaps; also, like the Otozoum, it has four toes; but the size of the toes does not accord with that of the Otozoum, nor is the structure of the foot the same, so far as we know. It has been suggested by Professor Agassiz, that this animal might have been a two-footed frog. Nature had, in those days, animal forms different from those we are acquainted with; and this might have been the fact with the Otozoum.

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GROUP SIXTH.

We have in this group a specimen of the track of a four-footed animal, which may have been a frog, though different from ours. The feet are unequal in size, and present a different number of toes. In existing frogs there are four toes in the fore feet, and five in the hind; but, in the specimen before us, the front toes are five in number, and the back toes three. It is called, therefore, ANOMOEPUS, unequal-footed. These impressions are in the red shale of Hadley, and very distinct. In some of them the lower leg is indicated, forming an impression six or seven inches long. The feet being smaller than the legs, the impression made by the latter is more expanded, superficial, and broader, yet still very definite. The opinion of President Hitchcock and Dr. Deane is, that the different impressions of five and three toes are those of the anterior and posterior extremities of one animal, which, from the size of the limbs, might be a frog three feet high.

On the same schist with these footmarks, are other curious impressions. The back of the slab is almost covered with the imprints of rain-drops. In the midst of these is a tridactylous impression, probably of a quadruped, crossed at its root by a single depression, nearly an inch broad, and two and a half long: this seems to form part of another broad superficial impression of about seven by four inches, which is probably also quadrupedal. Other parts present the impressions of nails and worm-tracks. At the opposite end is a deep, smooth, regular excavation, which might have been made by a Medusa.

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GROUP SEVENTH.

The seventh group contains the impressions of the feet of Saurians or lizards. We have a specimen of quadrupedal marks, with five toes to each foot, about an inch long, which may have been made by these animals. The impressions are small, but very distinct. There are lizards of the present day with five toes, about the size of these impressions; and these may, therefore, be set down as belonging to this order of reptiles. Like a number of the last-named specimens, they are in red shale.

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GROUP EIGHTH.

The eighth group is assigned by President Hitchcock to the Chelonian or turtle tribe. The slab bearing impressions of Brontozoum Gracillimum has a mark about fourteen inches long and two wide, which may be attributed to the plastron or breast-plate of the tortoise. On the slab from Turner's Falls there is a longitudinal furrow, which might have been made by the tail of a turtle; and in various of our slabs are impressions which we think belong to this tribe. We shall have occasion to notice hereafter remarkable tracks of these animals in the old red of Morayshire, in Scotland.

The most distinct of the traces of chelonians are on the large slab lately obtained for me by President Hitchcock from Greenfield. (Vide Plate.) This interesting slab contains the traces of quadrupeds, various birds, and two trails of chelonians: the largest of these is nearly five feet long, and four inches in diameter. The trail is composed of a number of parallel elevations, comparatively superficial.

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GROUP NINTH.

Of the ninth group, containing the marks of Annelidae, Crustacea, and Zoophytes, we have various specimens.

The impressions of insects do not seem as yet to have been distinguished on the ancient rocks. There is reason to believe, however, that many of the marks we discover in the rocky beds might have been made by the feet and bodies of large insects; and small species of the same tribes have been found imbedded in, and actually constituting, immense masses of calcareous and siliceous rocks.

The tracks of worms are numerous. No doubt these worms drew together a concourse of birds to the shores on which they rolled. On various slabs we find long cylindrical furrows, about the eighth of an inch in diameter, and of different lengths; one of them, in the slab from Dr. Deane, being eight or nine inches long. To these impressions the name of HERPYSTEZOUM, from herpystes, crawling, has been given. They vary, however, and some of them are very likely to be the tracks of the common earth-worm, or of some species of worm which existed when these rocks were formed. These impressions vary in length and in diameter; some of them are moderately regular, and others irregularly curved.

Very interesting tracks have been found in the ancient Potsdam white sandstone of Beauharnais, on the St. Lawrence, by Mr. Logan, an excellent geologist of Canada, and determined by Professor Owen to belong to Crustacea, crabs. The number of impressions made by each foot is sometimes seven, sometimes eight, and even more. This track, showing the traces of Crustacea, goes to form another link in the chain of fossil footsteps.

The Medusae, commonly called jelly-fish, dissolving as they do under the influence of the sun and air, would hardly be expected to leave their traces impressed on ancient rocks. Professor D'Orbigny, however, has watched the dissolution of these animals on the sea-shore, and found that, after wasting, they may leave their impressions on the sand; which, not being disturbed by a high tide for nearly a month, retains the impression of the zoophyte, and serves as a mould to receive materials which take a cast and transmit it to subsequent ages. We find one of these impressions on the slab of the Anomoepus Scambus; and President Hitchcock, having examined it, is of opinion that it retains the traces of a Medusa. The impression is about five inches in diameter, of a darker color and smoother texture than the rest of the rock. Its edges fade away gradually in the surface of the subjacent sandstone. A similar impression is found on the superior surface of the slab containing the Argozoum.

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GROUP TENTH.

The tenth group contains the HARPAGOPUS, a name derived from harpage, seizure, rapine. It is represented by President Hitchcock as having the form of a drag. The figure given by him resembles in a degree the foot of the African ostrich; being a long thick toe, with a shorter one, not unlike a thumb, on the side. An impression approximating this, but of small size, may be seen on the slab of the Anomoepus Scambus.

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The formation of bird-tracks is well represented by a clay specimen, about an inch thick, and ten inches long. This is a piece of dried clay, obtained by President Hitchcock from the banks of the Connecticut, and produced by washings from clay on the shore above, covered with foot-impressions of a small tridactylous bird, and dried in the sun. This piece shows, in a way not to be questioned, the manner in which the ancient vestiges were produced. Sir Charles Lyell noticed a similar fact on the banks of the Bay of Fundy.

ORGANIC IMPRESSIONS.

The second great division of fossil impressions is called ORGANIC, meaning impressions made by organized bodies; the bones of animals, fishes, and vegetables.