In tracing the evidences of creative power from the earlier to the later formations of the earth’s crust, remains of the Ichthyosaurus are first found in the lower lias, and occur, more or less abundantly, through all the superincumbent secondary strata up to, and inclusive of, the chalk formations. They are most numerous in the lias and oolite, and the largest and most characteristic species have been found in these formations.
No. 12.—Ichthyosaurus platyodon.
This most gigantic species, so called on account of the crown of the tooth being more flattened than in other species, and having sharp edges, as well as a sharp point, was first discovered in the lias of Lyme Regis, in Dorsetshire. Fossil remains now in the British Museum, and in the museum of the Geological Society, fully bear out the dimensions exhibited by the restoration of the animal as seen basking on the shore between the two specimens of Long-necked Plesiosaurs. The head of this species is relatively larger in proportion to the trunk, than in the Ichthyosaurus communis or Ichthyosaurus tenuirostris: the lower jaw is remarkably massive and powerful, and projects backwards beyond the joint, as far as it does in the crocodile. In the skull of an individual of this species, preserved in the apartments of the Geological Society of London, the cavity for the eye, or orbit, measures, in its long diameter, fourteen inches. The fore and hind paddles are large and of equal size.
The lias of the valley of Lyme Regis, Dorsetshire, is the chief grave-yard of the Ichthyosaurus platyodon; but its remains are pretty widely distributed. They have been found in the lias of Glastonbury, of Bristol, of Scarborough and Whitby, and of Bitton, in Gloucestershire; some vertebræ, apparently of this species, have likewise been found in the lias at Ohmden, in Germany.
No. 13.—Ichthyosaurus tenuirostris.
Behind the Ichthyosaurus platyodon, is placed the restoration of the Ichthyosaurus tenuirostris, or Slender-snouted Fish-lizard. The most striking peculiarity of this species is the great length and slenderness of the jaw-bones, which, in combination with the large eye-sockets and flattened cranium, give to the entire skull a form which resembles that of a gigantic snipe or woodcock, with the bill armed with teeth. These weapons, in the present species, are relatively more numerous, smaller, and more sharply pointed than in the foregoing, and indicate that the Ichthyosaurus tenuirostris preyed on a smaller kind of fish. The fore-paddles are larger than the hind ones. In the museum of the Philosophical Institution, at Bristol, there is an almost entire skeleton of the present species which measures thirteen feet in length. It was discovered in the lias of Lyme Regis. Portions of jaws and other parts of the skeletons of larger individuals have been found fossil in the lias near Bristol, at Barrow-on-Soar, in Leicestershire, and at Stratford-on-Avon. The Ichthyosaurus tenuirostris has also left its remains in the lias formation at Boll and Amburg, in Wirtemberg, Germany.
No. 14.—Ichthyosaurus communis.
Of this species, which was the most “common,” when first discovered in 1824, but which has since been surpassed by other species in regard to the known number of individuals, the head is restored, as protruded from the water, to the right of the foregoing species.
The Ichthyosaurus communis is characterised by its relatively large teeth, with expanded, deeply-grooved bases, and round conical furrowed crowns; the upper jaw contains, on each side, from forty to fifty of such teeth. The fore-paddles are three times larger than the hind ones. With respect to the size which it attained, the Ichthyosaurus communis seems only to be second to the Ichthyosaurus platyodon. In the museum of the Earl of Enniskillen, there is a fossil skull of the Ichthyosaurus communis which measures, in length, two feet nine inches, indicating an animal of at least twenty feet in length.