An ichthyosaur (Greek for 'fish lizard') was a marine reptile that lived during a large part of the Mesozoic period. They appeared slightly earlier than dinosaurs (250 million years ago versus 230 ma) and disappeared earlier, too, about 90 ma. During the early Triassic, Ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water (analogous to dolphins and whales). They were particularly abundant in the Jurassic period. They belong to the order Ichthyosauria.

Ichthyosaurs looked like fish, averaging 2 to 3 metres in length. They had 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, air-breathing and viviparous. Built for speed, like modern tuna, they also apparently were deep divers, like some modern whales.

The earliest ichthyosaurs, looking more like finned lizards than the familiar fish or dolphin forms, are known from the Lower Triassic strata of Canada, China, Japan, and Spitsbergen in Normay. Late Jurassic Himalayasaurus tibetensis was found, as you may have suspected, in Tibet. The largest Ichthyosaurs exceeded 15 meters.

Many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites for their food.Some early Ichthyosaurs had yeeth adapted for crushing shellfish. Ichthyosaurs ranged so widely in size, and survived so long, they are likely to have had a wide range of prey.

Typical ichthyosaurs have very large eyes, protected within a bony ring. Did they hunt at night?

The first Ichthyosaur fossil was found by Mary Anning in Lyme Regis, along what is now called the Jurassic Coast, in 1811. An ichthyosaur is the State Fossil of Nevada, which was a shallow Jurassic inland ocean.

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