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On the shore at Lyme Regis, these Coprolites are so abundant that they lie in some parts of the lias like potatoes scattered in the ground; still more common are they in the lias of the Estuary of the Severn, where they are
Society of London, 1829, (vol. iii. N. S. part i. p. 224, with three plates.)
"In variety of size and external form, the Coprolites resemble oblong pebbles or kidney-potatoes. They, for the most part, vary from two to four inches in length, and from one to two inches in diameter. Some few are much larger, and bear a due proportion to the gigantic calibre of the largest Ichthyosauri; others are small, and bear a similar ratio to the more infantine individuals of the same species, and to small fishes: some are flat and amorphous, as if the substance had been voided in a semifluid state; others ore flattened by pressure of the shale. Their usual colour is ash-gray, sometimes interspersed with black, and sometimes wholly black. Their substance is of a compact earthy texture, resembling indurated elay, and having a conchoidal and glossy fracture. The structure of the Coprolites at Lyme Regis is in most cases tortuous, but the number of coils is very unequal; the most common number is three: the greatest I have seen is six: these variations may depend on the various species of animals from which they are derived; I find analogous variations in the tortuous intestines of modern Skates, Sharks, and Dog-fish. Some Coprolites, especially the small ones, show no traces at all nf contortion.
"The sections of these foecal balls, (see PI. 15, Figs. 4, and 6,) show their interior to be arranged in a folded plate, wrapped spirally round from the centre outwards, like the whorls of a turbinated shell; their exterior also retains the corrugations and minute impressions, which, in their plastic state, they may have received from the intestines of the living animals. (See PI. 15, Figs. 3, and 10 to 14.) Dispersed irregularly and abundantly throughout these petrified feces, are the scales, and occasionally the teeth and bones of fishes, that seem to have passed undigested through the bodies of the Saurians; just as the enamel of teeth and sometimes fragments of bone, are found undigested both in the recent and fossil album gra?cum of hyaenas. These scales are the hard bright scales of the Dapedium poliium, and other fishes which abound in the lias, and which thus appear to have formed no small portion of the food of the Saurians. The bones are chiefly vertebras of fishes and of small Ichthyosauri; the latter are less frequent than the bones of fishes, but still arc sufficiently numerous, to show that these monsters of the ancient deep, like many of their successors in our modern oceans, may have devoured the small and weaker individuals of their own species."
similarly disposed in strata of many miles in extent, and mixed so abundantly with teeth and rolled fragments of the bones of reptiles and fishes, as to show that this region, having been the bottom of an ancient sea, was for a long period the receptacle of the bones and fcecal remains of its ^habitants. The occurrence of Coprolites is not, however, peculiar to the places just mentioned; they are found in greater or less abundance throughout the lias of England; they occur also in strata, of all ages that contain the remains of carnivorous reptiles, and have been recognised in many and distant regions both of Europe and America.*
The certainty of the origin of these Coprolites is established by their frequent presence in the abdominal region of fossil skeletons of Ichthyosauri found in the lias of Lyme Regis. One of the most remarkable of these is represented in PI. 13; the coprolitic matter loaded with fish-scales, within the ribs of these and similar specimens, is identical in appearance and chemical composition with the insulated coprolites that occur in the same strata with the skeletons.! The preservation of such fecal matter, and its conversion to the state of stone, result from the imperishable nature of the phosphate of lime, of which both bones, and the products of digested bones are equally composed.
* Professor Jaeger has recently discovered many Coprolites in the alum slate of Gaildorf in Wirtemberg; a formation which he considers to be in the lower region of that part of the new red sandstone formation which in Germany is called Keuper; and which contains the remains of two species of Saurian?.
In the United States Dr. Dekay has also discovered Coprolites in tho Greenland formation of Monmouth, in New Jersey, see PI. 15, Fig, 1)3..
\ This specimen has been presented by Viscount Cole to the Geological Collection of the University of Oxford. It affords decisive proof that the substances in question cannot be referred to adventitious matter,, placed accidentally in contact with the fossil body, inasmuch as the large coprolitic mass is enclosed between the back bone and the right and left series of ribs, of which the greater number remain nearly in their natural: position. The quantity of this coprolite is prodigious, when compared with the size of the animal in which it occurs; and if we were not acquainted with the powers of the digestive organs of reptiles and fishes, and their capacity of gorging the larger animals tiiat form their prey ; the great space within these fossil skeletons of Ichthyosauri, which is occasionally filled with coprolitic matter, would appear inexplicable
The skeleton of another Ichthyosaurus in the Oxford Museum, from the lias at Lyme Regis, (PI. 14) shows a large mass of fish scales, chiefly referable to the Pholidophorus, limbatus,* intermixed with coprolite throughout the entire region of the ribs; this mass is overlaid by many ribs, and although, in some degree perhaps, extended by pressure, it shows that the length of the stomach was nearly co-extensive with the trunk.
* According to Professor Agassiz, the scales of Pholidophorus limbatus, a species very frequent among the fossils of the lias, arc more abundant than those of any other fish in the Coprolites found in that formation at Lyme Regis; and show that this species was the principal food of these reptiles. In Coprolites from the coal formation, near Edinburgh, he has also recognised the scales of Palseoniscus, and of other fishes that are often found entire in strata that accompany the coal of that neighbourhood. Scales of the Geryx armatus, a fish discovered by Mr. Mantell, in the chalk, occur in Coprolites derived from voracious fishes during the deposition of this formation.
A Coprolite from the lias, (PI. 15, Eig. 3,) remarkable for its spiral convolutions, and vascular impressions, affords a striking example of the minute accuracy with which investigations are now conducted by naturalists, and of the kind of evidence which comparative anatomy contributes in aid of geological inquiry. On one side of this Coprolite, there is a small scale, (Fig. 3, a,) which I could only refer to some unknown fish, of the numerous species that occur in the lias. The instant I showed it to M. Agassiz, he not only pronounced its species to be the Pholidophorus limbatus; but at once declared the precise place which this scale had occupied upon the body of the fish. A minute tube upon its inner surface, (PI. 15, Fig. 3',) scarcely visible without a microscope, showed it to have been one of those which form the lateral line of perforated scales, that pass from the head towards the tail, one on each side of every fish: and convey a tube for the transmission of lubricating mucus from glands in the head, to the extremity of the body. The place of the scale in this line, had been on the left side, not fir from the head. Fig. 3", is the upper surface of a similar scale, showing at e the termination of the mucous duct.
Among living voracious reptiles we have examples of stomachs equally capacious; we know that whole human bodies have been found within the stomachs of large Crocodiles; we know also, from the form of their teeth, that the Ichthyosauri, like the Crocodiles, must have gorged their prey entire; and when we find, imbedded in Coprolites derived from the larger Ichthyosauri, bones of smaller Ichthyosauri, of such dimensions, (see PL 15, Fig. 18. And Geol. Trans. 2, S. vol. iii., PI. 29, Figs, 2, 3, 4, 5,) that the individuals from which they were derived, must have measured several feet in length; we infer that the stomach of these animals formed a pouch, or sac, of prodigious size, extending through nearly the entire cavity of the body, and of capacity duly proportioned to the jaws and teeth with which it co-operated.
Spiral Disposition of Small Intestines.
As the more solid parts of animals alone, are usually susceptible of petrifaction, we cannot demonstrate by direct evidence the form and size of the small intestines of the Ichthyosauri, but the contents of these viscera are preserved in such perfection in a fossil state, as to afford circumstantial evidence that the bowels in which they were moulded, were formed in a manner resembling the spiral intestines of some of the swiftest and most voracious of our modern fishes.
We shall best understand the structure of these intestines by examining the corresponding organs of Sharks and Dog-fish, animals not less peculiarly rapacious among the inhabitants of our modern seas, than the Ichthyosauri were in those early periods to which our considerations are carried back. We find in the intestines of these fishes, (see PI. 15, Figs. 1, and 2,) and also in those of Rays, an arrangement resembling that of the interior of an Archimedes screw, admirably adapted to increase the extent of internal surface for the absorption of nutriment from the food, during its passage through a tube containing within it a continuous spiral fold, coiled in such a manner, as to afford the greatest possible extent of surface in the smallest space. A similar contrivance is shown by the Coprolites to have existed in the Ichthyosaurus. See PI. 15, Figs. 3, 4, 6.*
Impressions of the Mucous Membrane on Coprolites. Besides the spiral structure and consequent shortness of
* These cone-shaped bodies are made up of a flat and continuous plate of digested bone coiled round itself whilst it was yet in a plastic state. The form is nearly that which would be assumed by a piece of riband, forced continually forward into a cylindrical tube, through a long aperture in its side. In this case, the riband moving onwards, would form a succession of involuted cones, coiling one round the other, and after a certain number of turns within the cylinder, (the apex moving continually downwards,) these cones would emerge from the end of the tube in a form resembling that of the Coprolites, PI. 15, Figs. 3, 5, 7,10, 11,12, 13, 14. In the same manner, a lamina of coprolitic matter would be coiled up spirally into a series of successive cones, in the act of passing from a small spiral vessel into the adjacent large intestine. Coprolites thus formed fell into soft mud, whilst it was accumulating at the bottom of the sea, and together with this mud, (which has subsequently been indurated into shale and stone,) they have undergone so complete a process of petrifaction, that in hardness, and beauty of the polish of which they are susceptible, they rival the qualities of ornamental marble.
Fig. 6, shows a longitudinal section through the axis of a coprolite, from, the inferior chalk, in which this involute conical form is well defined. Fig. 4, is the transverse section of another Coprolite from the lias, showing the manner in which the plate coils round itself, till it terminates externally in a broken edge (at b.) In all the figures the letter b, marks the transverse section of this plate, where it is broken off near the termination of its outer coil; the sections at b, show also the size and form of the flattened passage through the interior of the screw.
A lamina of tenacious plastic substance pressed continually forwards from the interior of such a screw, into the cavity of the large intestine, would coil up spirally within it, until it attained the largest size admitted by its diameter; from this coil successive portions would be broken off abruptly, (at b,) and descending into the cloaca would be thence discharged into the sea.