The typical fish lizards belong to this large family, which flourished throughout the Jurassic period and into the Cretaceous. They are known from some remarkably well-preserved specimens, which show them to be highly specialized marine animals.
The ichthyosaurs had developed a streamlined body, torpedo-shaped, with a stabilizing dorsal fin on the back; short, paired paddles for steering; and a strong, fishlike tail with 2 equal lobes for swimming. Ball-and-socket joints between the tail vertebrae allowed for powerful strokes from side to side. The tail, together with the great flexibility of the backbone, propelled the animal rapidly through the water — the swimming method used by modern, fast-moving fishes.
eurhinosaurus ophthalmosaurus temnodontosaurus name: Ichthyosaurus time: Early Jurassic to Early
Cretaceous locality: Europe (England and
Germany), Greenland and North
America (Alberta) size: up to 6 ft 6 in/2 m long Ichthyosaurus is one of the best-known prehistoric animals, since a graphic record of its remains are preserved in the shales of southern Germany, near Holz-maden. These rocks were laid down in shallow waters during the Early Jurassic.
Several hundred complete skeletons of Ichthyosaurus have been found, their bones still articulating with each other. The tiny bones of their young were also found inside the bodies of several adults. This — combined with some specimens where the young is preserved actually emerging from the body of the adult (tail-first, as in modern whales) — shows without a doubt that these marine reptiles gave birth to live young at sea.
The find in Germany also yielded a unique picture of how the animals looked in life. A thin film of carbon had been laid down around many of the specimens, outlining the exact shape of their bodies when the flesh was still on the bones. The characteristic features of a typical ichthyosaur can be clearly seen — the high dorsal fin on the back; the half-moon shape of the tail (caudal) fin, with the backbone angled down sharply into its lower lobe; and the short, hydrofoil-shaped paddles that enclosed the greatly elongated toes of the limbs, the front pair longer than the hind pair.
The nostrils of Ichthyosaurus were set far back on its snout near the eyes, so the animal only had to break the surface of the water to breathe. The bones of the ear were massive, and probably transmitted vibrations from the water to the inner ear, so that the direction of potential prey could be judged. But Ichthy osaurus' main sense for locating its prey would have been sight — its eyes were large and, most probably, extremely sensitive.
Even fossil droppings (called copro-lites) and stomach contents of these marine reptiles have been preserved in the rocks. They confirm that fish constituted the bulk of the diet, but that cephalopods were also eaten, such as the straight-shelled belemnites.
The remains of pigment cells have also been preserved, and analysis of these suggests that the smooth, thick skin of Ichthyosaurus was a dark reddish-brown color in life.
name: Ophthalmosaurus time: Late Jurassic locality: Europe (England and
France), North America (Western
USA and Canadian Arctic) and
South America (Argentina) size: 11 ft 6 in/3.5 m long Ophthalmosaurus was even more streamlined than its contemporary, Ichthyosaurus (above). Its body was shaped almost like a teardrop — massive and rounded at the front, and tapering toward the rear to culminate in the great, half-moon-shaped caudal fin. Its front limbs were much more developed than the hindlimbs, indicating that the front paddles did most of the steering and stabilizing work, with the tail propelling the body from the rear.
The most remarkable feature of Ophthalmosaurus was its huge eyes. Their sockets are about 4 in/10 cm in diameter, and occupy almost the whole depth of the skull on each side. A ring of bony plates (sclerotic ring) surrounded each eyeball, to prevent the soft tissues from collapsing under the external water pressure, and to help with focusing. (The eyes of all ichthyosaurs had these sclerotic rings, but they are particularly noticeable in Ophthalmosaurus.)
The super-large eyes of this ichthyosaur suggest that it was a night-feeder. It probably hunted close to the surface, feeding on squid, which in turn were feeding on the plankton-eating fish.
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