The ostrich-tracks present a numerous natural and most remarkable
group; remarkable from the great size of some species,--all of them
tridactylous and pachydactylous. The ostrich of the Old World has only
two toes, but this family exists in South America at the present time
under the name of Rhea Americana; and tracks of an animal, probably of
the same family, are found in the numerous impressions near
Connecticut River,--all of them having three toes in front, and the
rudiment of a fourth behind.
This group contains a number of genera. The FIRST GENUS, denominated
_Brontozoum_, presents the tracks of a most extraordinary bird. These
tracks appear less questionable since the discovery in Madagascar of
the eggs of the Epyornis.
The tracks of the largest species, the BRONTOZOUM GIGANTEUM, are
four times the magnitude of those made by the existing ostrich of
Africa. They are very numerous, and congregated together. The foot of
the Brontozoum Giganteum, including the inferior extremity of the
tarso-metatarsal bone, which makes a part of the foot, measures in our
specimen twenty inches; in the Mastodon Giganteus, the foot measures
twenty-seven inches; the width also is less, being ten inches across
the metacarpals, while that of the Mastodon is twenty-two: but the one
is a bird, the other a quadruped. The toes are three in number, and
present the same divisions with existing birds; the inner toe having
three, the middle four, the outer five phalanges. Some of the
articulations of the toes of this noble specimen are remarkable for
the manner in which they illustrate the mode of formation of the
tracks. These phalanges have become separated from the solid rock in
which they were encased, so as to be removable at pleasure; and they
thus show that the whole foot is not a simple impression in the rock
which contains it, but a depression filled by foreign materials, i.e.
by sand, clay, and other relics of pre-existing rocks. These materials
had been gradually deposited in the mould formed by the bird's foot,
and are therefore independent of this rock, in the same way as the
plaster-of-Paris cast of a tooth, or any other body, is independent of
the mould to which it owes its form. The impressions are in gray
sandstone.
On the reversed surface of the slab is seen a small piece of broken
quartz, about half an inch square. This piece forms a beautiful
illustration of a part of the process by which the sandstone rocks are
formed.
The second species of the same genus is the BRONTOZOUM SILLIMANIUM.
Of this we have three specimens; the tracks have the same general
character with the preceding, but are smaller.
The third species of this genus is styled the BRONTOZOUM LOXONYX,
from _loxos_, a _bow_, and _onyx_, a _nail_,--a curved nail. It is
smaller than the Sillimanium, and has the nail set to one side.
The fourth species, still smaller, is the Brontozoum Gracillimum. On
this slab the impressions are in relief; viz.: 1st, of Brontozoum
Gracillimum; 2d, of Brontozoum Parallelum; 3d, of the track of a
tortoise, fourteen inches long, and two wide. Other extensive
eminences and depressions, with rain-drops, may be observed on the
same surface.
The fifth species is called BRONTOZOUM PARALLELUM, from the tracks
being on a line with each other. Of this there are two specimens, one
of them, however, being a single track. On the surface of the other
slab there are at least five distinct tracks, one of them being a
small new and undescribed species,--thus making the whole number of
species of Brontozoum which we possess to be at least six.
The SECOND GENUS of Struthiones is called _AEthyopus_, from
_aithuia_, a _gull_, and _pous_, a _foot_,--gull-footed. This genus
is smaller than the Brontozoum Giganteum; and we have two species,
viz. the AETHYOPUS LYELLIANUS, which is the larger, and two specimens
of AETHYOPUS MINOR. All of these are distinguished from the preceding
genus by the winged foot, and in the Lyellianus by the shallowness of
the impression. The AEthyopus Minor is not always distinguished by the
superficiality of its impression. This is sometimes deep. Therefore
this character may not be considered a distinctive one, or the
AEthyopus Minor might be referred to another genus. Of the two
specimens of this latter species, the first is in depression,
tridactylous. The depressions are deep with rain-drops, marks of
quadrupeds and zoophytes over the whole surface. The ornithichnic
impressions are two in number; one superficial, the other very deep.
The reversed surface of this slab contains one tridactylous impression
in relief. The second specimen has three depressions; two of which are
superficial, and the third is quite deep, displaying, by a depressed
surface, the webbed character of the foot.
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