Bayle appears to have furnished the best idea of the Ichthyosaurus by describing it as the Whale of the Saurians—the Cetacean of the primitive seas. It was, in fact, an animal exclusively marine; which, on shore, would rest motionless like an inert mass. Its whale-like paddles, and fish-like vertebræ, the length of the tail and other parts of its structure, prove that its habits were aquatic; as the remains of fishes and reptiles, and the form of its teeth, show that it was carnivorous. Like the Whale, also, the Ichthyosaurus breathed atmospheric air; so that it was under the necessity of coming frequently to the surface of the water, like that inhabitant of the deep. We can even believe, with Bayle, that it was provided, like the Whale, with vents or blowers, through which it ejected, in columns into the air, the water it had swallowed.
Fig. 96.—Ichthyosaurus platydon.
The dimensions of the Ichthyosaurus varied with the species, of which five are known and described. These are Ichthyosaurus communis, I. platydon, I. intermedius, I. tenuirostris, and I. Cuvierii, the largest being more than thirty feet in length.
Fig. 97.—Lower jaw of Ichthyosaurus. (Dr. Buckland.)
The short, thick neck of the Ichthyosaurus supported a capacious head, and was continued backwards, from behind the eyes, in a column composed of more than a hundred vertebræ. The animal being adapted, like the whale, for rapid movement through the water, its vertebræ had none of the invariable solidity of those of the Lizard or Crocodile, but rather the structure and lightness of those of Fishes. The section of these vertebræ presents two hollow cones, connected only by their summits to the centre of the vertebræ, which would permit of the utmost flexibility of movement. The ribs extended along the entire length of the vertebral column, from the head to the pelvis. The bones of the sternum, or that part of the frame which supported the paddles, present the same combinations with those of the sternum in the Ornithorhynchus, or Duck-billed Platypus, of New Holland, an animal which presents the singular combination of a mammalian furred quadruped having the bill of a duck and webbed feet; which dived to the bottom of the water in search of its food, and returned to the surface to breathe the air. In this phenomenon of living Nature the Creator seems to have repeated, in our days, the organic arrangements which he had originally provided for the Ichthyosaurus.
In order that the animal should be able to move with rapidity in the water, both its anterior and posterior members were converted into fins or paddles. The anterior fins were half as large again as the posterior. In some species each paddle was made up of nearly a hundred bones, of polygonal form, and disposed in series representing the phalanges of the fingers. This hand, jointed at the arm, bears resemblance, in osteological construction, to the paddles, without distinct fingers, of the Porpoise and the Whale. A specimen of the posterior fin of I. communis, discovered at Barrow-on-Soar, in Leicestershire, in 1840, by Sir Philip Egerton, exhibited on its posterior margin the remains of cartilaginous rays, which bifurcated as they approached the edge, like those in the fins of a fish. “It had previously been supposed,” says Professor Owen, “that the locomotive organs were enveloped, while living, in a smooth integument, like that of the turtle and porpoise, which has no other support than is afforded by the bones and ligaments within; but it now appears that the fin was much larger, expanding far beyond the osseous frame-work, and deviating widely in its fish-like rays from the ordinary reptilian type.” The Professor believes that, besides the fore-paddles, these stiff-necked Saurians were furnished at the end of the tail with a fin to assist them in turning, not placed horizontally, as in the whale, but vertically, forming a powerful instrument of progression and motion. It is obvious that the Ichthyosaurus was an animal powerfully armed for offence and defence. We cannot say, with certainty, whether the skin was smooth, like that of the whale or lizard, or covered with scales, like the great reptiles of our own age. Nevertheless, as the scales of the Fishes and the cuirass and horny armour of other Reptiles of the Lias are preserved, and as no such defensive scales have been found belonging to the Ichthyosaurus, it is probable that the skin was naked and smooth. The tail, composed of from eighty to eighty-five vertebræ, was provided with large and long paddles, arranged vertically as in the Whale.