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Ichthyosaurs were large marine reptiles that lived between 230 and 90 million years ago, resembling fish or dolphins. They evolved from terrestrial reptiles and were not dinosaurs. Most were 2 to 4 meters long and had large protruding eyes, eating meat. They went extinct in the Cretaceous period.
Ichthyosaurs, whose name means “fish lizard” in Greek, were large marine reptiles that lived between 230 and 90 million years ago. They superficially resembled fish or dolphins. Ichthyosaurs shared the Earth’s seas with sharks, fish, and other marine reptiles such as plesiosaurs and pliosaurs. Ichthyosaurs were first described from fossil fragments excavated in 1699 in Wales.
Ichthyosaurs evolved just 21 million years after the largest mass extinction in history and disappeared about 25 million years before the mass extinction that killed the dinosaurs. Although ichthyosaurs are sometimes incorrectly called dinosaurs, they weren’t. The fish-like body structure of ichthyosaurs has led biologist Stephen Jay Gould to call them his favorite example of parallel evolution.
The evolution of ichthyosaurs into spindly dolphin-like forms is made all the more remarkable by the fact that they evolved from terrestrial reptiles with no bodily features to work with; not even a small caudal fin. Early ichthyosaurs were small (about a meter long) and lacked the long fins of later ichthyosaurs, which instead swam in an undulating, eel-like motion.
Most ichthyosaurs were 2 to 4 m (6.6 to 13.2 ft) long, with a porpoise-like head, long snout, and sharp teeth. Some reached 55 m in length, such as Shonisaurus, the state fossil of Nevada, although they were much larger and much less typical. The largest was Shonisaurus sikanniensis, the largest known marine reptile at 17 m (21 ft). The largest ichthyosaurs died out as a result of extinctions at the end of the Triassic period.
Most ichthyosaurs had large, protruding eyes. They ate meat, especially fish and occasionally seabirds or young marine reptiles. The flagship of the ichthyosaurs was in the Triassic and they evolved around the same time as the dinosaurs. After the Triassic and early Jurassic, their diversity went downhill, and by the mid-Jurassic, all ichthyosaurs belonged to a single clade. Ichthyosaurs then went extinct in the Cretaceous, one of the few major groups to go extinct on their own and not as a result of the mass extinction at the end of the period.
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