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Ichthyosaurs averaged 2 to 3 metres in length, with a porpoise-like head and a long, toothed snout. They had a large tail fin and their limbs were adapted for use as steering paddles. They were carnivorous, coming to the surface to fill their lungs with air and viviparous, for fossils have been found with their fossilized fetal young. Built for speed, like modern tuna, they also apparently were deep divers, like some modern whales.

Although they looked like fish they were not. Biologist Stephen Jay Gould said the ichthyosaur was his favorite example of convergent evolution, where similarities of structure are analogous not homologous, for this group

"converged so strongly on fishes that it actually evolved a dorsal finDorsal Fin of the Orca A dorsal fin is a fin located on the backs of fishes, whales, dolphins and porpoises. Its main purpose is to stabilise the animal against rolling and assist in sudden turns. Some animals have developed dorsal fins with protective fu and tail in just the right place and with just the right hydrological design. These structures are all the more remarkable because they evolved from nothing— the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor."

In fact the earliest reconstructions of ichthyosaurs omitted the dorsal fin, which had no hard skeletal structure, until finely-preserved specimens recovered in the 1890sEvents and trends Technology Early commercial production of automobiles. Science Henri Becquerel discovers radioactivity Discovery of x-rays by Wilhelm Rontgen Swedish scientist Svante Arrhenius and US geologist Thomas Crowder Chamberlain independently co from the Holzmaden lagerstättenLagerstatten ( German, singular: Lagerstatte are sedimentary deposits that exhibit extraordinary fossil richness and completeness. The German word literally translates as "resting places. Palaeontologists distinguish two kinds: Konzentrat-Lagerstatten sig in GermanyThe Federal Republic of Germany ( German: Bundesrepublik Deutschland is one of the world's leading industrialized countries, located in the middle of the European Union. It is bordered to the north by the North Sea, Denmark and the Baltic Sea, to the east revealed traces of the fin. The earliest ichthyosaurs, looking more like finned lizards than the familiar fish or dolphin forms, are known from the Lower Triassic strata of CanadaCanada historically the Dominion of Canada is the second-largest, and northernmost, country in the world. It is a decentralized federation of 10 provinces and 3 territories, governed as a constitutional monarchy, and formed in 1867 through an act of Confe, ChinaThis article is on the geographic and cultural entity. For other meanings, see China (disambiguation). China ( Traditional Chinese: , Simplified Chinese: , Hanyu Pinyin: Zhongguo, Wade-Giles: Chung-kuo) is a country in continental East Asia with some oute, Japan, and Spitsbergen in Norway. Meanwhile the Late Jurassic Himalayasaurus tibetensis was found in Tibet. The largest ichthyosaurs exceeded 15 meters.

For their food, many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites. Some early ichthyosaurs had teeth adapted for crushing shellfish. Ichthyosaurs ranged so widely in size, and survived for so long, that they are likely to have had a wide range of prey. Typical ichthyosaurs have very large eyes, protected within a bony ring, suggesting they may have hunted at night.