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Ichthyosaurs continued to evolve during the Triassic period, and both dolphin-like and somewhat serpent-like forms existed, the latter sometimes growing to huge sizes, as much as 50 feet (15 meters) in length. By the early Jurassic period, Ichthyosaurs had reached their peak of diversity, and a long slow decline in diversity continued through the Jurassic and into the Cretaceous period. The last Icthyosaurs finally became extinct during the middle to late Cretaceous, perhaps about 90 million years ago.
In outward physical form, Ichthyosaurs tend to resemble whales, dolphins or sharks. This is a result of convergent evolution - sharks, cetaceans (whales, dolphins and porpoises), and ichthyosaurs all evolved similar body shapes, because it is a good hydrodynamic solution for swimming.
One difference between Ichthyosaurs and many other marine predators, is that it is believed that Ichthyosaurs probably hunted by sight (rather than for example echo-location). Part of the evidence for this is that Ichthyosaurs generally had comparatively large eyes - one particular genus of Ichthyosaur, namely Temnodontosaurus which lived in Jurassic Europe and was about 30 feet (12 meters) long, had the largest eyes of any known vertebrate - its eyes were 10 inches (26 centimeters) in diameter.
Another noteworthy fact about Ichthyosaurs is that at least some species, perhaps even all species, seem to have given birth to live young. The evidence for this is that fossils have been found of Ichthyosaurs containing fossils of babies within the abdomen. It has been suggested that perhaps these babies were stomach contents and therefore evidence of cannibalism, however it seems more likely that these fossils show a pregnant Ichthyosaur that died just before (or perhaps even during) giving birth.
Fossil fragments of Ichthyosaurs have been known since at least 1699, however the the first complete fossil specimen was found by Mary Anning in 1811 in Lyme Regis, England (Mary Anning subsequently discovered three species of Ichthyosaur). A large number of other fossils were also found by a 1905 expedition to central Nevada, including a 55 foot (17 meter) Shonisaurus (a very large, late Triassic Ichthyosaur), which since 1977, has been designated as Nevada's State Fossil.
Ichthyosaurs were marine reptiles that lived between 245 and 90 million years ago
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