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The Collaborative International Dictionary

Ichthyosaur \Ich"thy*o*saur\, n. [Cf. F. ichthyosaure.] (Paleon.) One of the Ichthyosaura.

Douglas Harper's Etymology Dictionary

extinct reptile, 1830, Modern Latin, from Greek ikhthys "fish" + sauros "lizard" (see -saurus).


n. Any of several extinct fishlike reptiles, of the order ''(taxlink Ichthyosauria order noshow=1)'', that had a body somewhat like a porpoise. (from c. 1830)

  1. n. any of several marine reptiles of the Mesozoic having a body like a porpoise with dorsal and tail fins and paddle-shaped limbs

  2. [also: ichthyosauruses (pl)]


Ichthyosaurs ( Greek for "fish lizard" - ιχθυς or ichthys meaning "fish" and σαυρος or sauros meaning "lizard") are large marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' - a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria).

Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 250 million years ago ( mya) and at least one species survived until about 90 million years ago, into the Late Cretaceous. During the early Triassic Period, ichthyosaurs evolved from a group of unidentified land reptiles that returned to the sea, in a development parallel to that of the ancestors of modern-day dolphins and whales, which they gradually came to resemble in a case of convergent evolution. They were particularly abundant in the later Triassic and early Jurassic Period, until they were replaced as the top aquatic predators by another marine reptilian group, the Plesiosauria, in the later Jurassic and Cretaceous Period. In the Late Cretaceous, ichthyosaurs became extinct for unknown reasons.

Science became aware of the existence of ichthyosaurs during the early nineteenth century when the first complete skeletons were found in England. In 1834, the order Ichthyosauria was named. Later that century, many excellently preserved ichthyosaur fossils were discovered in Germany, including soft tissue remains. Since the late twentieth century, there has been a revived interest in the group leading to an increased number of named ichthyosaurs from all continents, over fifty valid genera being now known.

Ichthyosaur species varied from one to over sixteen metres in length. Ichthyosaurs resembled both modern fish and dolphins. Their limbs had been fully transformed into flippers, which sometimes contained a very large number of digits and phalanges. At least some species possessed a dorsal fin. Their heads were pointed, the jaws often equipped with conical teeth to catch smaller prey. Some species had larger bladed teeth to attack large animals. The eyes were very large, probably for deep diving. The neck was short and later species had a rather stiff trunk. These also had a more vertical tail fin, used for a powerful propulsive stroke. The vertebral column, made of simplified disc-like vertebrae, continued into the lower lobe of the tail fin. Ichthyosaurs were air-breathing, bore live young, and were probably warm-blooded.

Usage examples of "ichthyosaur".

These plates may have changed the shape of the eyeball in response to water pressure, allowing the prey to remain in focus as the ichthyosaur chased after it.

The baby was found in marine deposits, but it is not certain whether the baby hatched on land and died at sea, or if it was born live at sea like an ichthyosaur and then died.

There was ring of bone within the eyehole, as in the ichthyosaur which probably had a similar function.

High Priest looked down at the monster, a gigantic ichthyosaur, swimming back and forth in the deep pool, the surface of which was about ten feet below the bottom tier of seats.

The sea serpent disemboweled it, ripping open the tough hide and spilling ichthyosaur entrails into the stormy subterranean sea.

Save for its long, beaklike snout, the ichthyosaur resembled a supershark, forty feet from snout to tail, and every inch of that forty feet crammed with mindless hunger and ferocity.

However, reptiles flourished in the Jurassic open oceans and seas, where ichthyosaurs, plesiosaurs, and sharks were abundant.

It seemed clear that McInturff and his egg-hunting cohorts would either hang me from a willow tree or paddle me out to sea and toss me overboard to the archaic fishes or ichthyosaurs that yet remained.

In the sea, this included the mosasaurs, plesiosaurs, and ichthyosaurs, and in the air, pterosaurs.

The end of the tail was bent downward, as in advanced ichthyosaurs, suggesting the presence of a large vertical fluke.

Vision appears to have been acute in ichthyosaurs, as in most predators.

Carbonized skin impressions have been found around the skeletons of ichthyosaurs in the black shales at Holzmaden, Germany.

Holzmaden reveal baby ichthyosaurs within the body of the mother, indicating that the young were born live.

Appearing in the oceans about the same time as the ichthyosaurs were another group of euryapsid reptiles called the nothosaurs.

The limbs of nothosaurs show none of the modifications seen in ichthyosaurs and they could have supported the adult on land if they came ashore to lay eggs.