Prehistoric life
Ichthyosaurs were predatory marine reptiles that swam the world's oceans while dinosaurs walked the land. They appeared in the Triassic period, dying out around 25 million years before the extinction event that wiped out the dinosaurs. Ichthyosaurs (literally 'fish-lizards') evolved from an as yet unidentified land reptile that moved back into the water. These huge animals rapidly diversified from being lizards with fins to developing a much more streamlined, fish-like form built for speed. One species has been calculated to have a cruising speed of 36 km/h. These enormous predators remained at the top of the food chain until they were replaced by the plesiosaurs.
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Sea monsters
Plesiosaur and ichthyosaur bone fossils are found at Nash Point in Wales.
Plesiosaur and ichthyosaur bone fossils are found at Nash Point in Wales.
Dorset's ancient animals
Simon King shows off Dorset's coastal fossil riches including a huge ichthyosaur.
Simon King shows off Dorset's coastal fossil riches including a huge ichthyosaur.
A reptilian dolphin?
Dolphins give clues as to how prehistoric ichthyosaurs may have lived.
Dolphins give clues as to how prehistoric ichthyosaurs may have lived.
Discover what these behaviours are and how different plants and animals use them.
Additional data source: Animal Diversity Web
Discover the other animals and plants that lived during the following geological time periods.
Learn more about the other animals and plants that also form these fossils.
Ichthyosaurs (Greek for "fish lizard" - "ιχθυς" or "ichthys" meaning "fish" and "σαυρος" or "sauros" meaning "lizard") were giant marine reptiles that resembled dolphins in a textbook example of convergent evolution. Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 245 million years ago (mya) and at least one species survived until about 90 million years ago, into the early Cretaceous. During the middle Triassic Period, ichthyosaurs evolved from a group of, as yet, unidentified land reptiles that moved back into the water, in a development parallel to that of the ancestors of modern-day dolphins and whales. They were particularly abundant in the Jurassic Period, until they were replaced as the top aquatic predators by another reptilian order, the plesiosaurs, in the Cretaceous Period. 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).
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Adapted to swimming
Carnivorous
Predator
Viviparous
