Opthalmosaurus, and advanced ichthyosaur


Ichthyosaur means 'fish-lizard'.

They are the most highly specialised of all marine reptiles, and are so different from nothosaurs and plesiosaurs that it is thought the euryapsid skull condition probably evolved independently in this group by convergent evolution.

Ichthyosaurs were completely adapted for an aquatic lifestyle, and there is evidence that they gave birth to live young in the water rather than laying eggs on land. Some skeletons have been found with embryos fossilied inside them.


An ichthyosaur embryo

Early ichthyosaurs were elongate animals with legs modified into paddles, hyperphalangy (addition of joints to toes) and hyperdactyly (addition of extra digits). The spine turned downwards to produce a hypocercal tail (the vertebral column bends downwards into the lower half of the tail).

Ichthyosaurs reached 2-4m in length. They had long skulls, with many simple pointed teeth, with which they hunted fish and cephalopods (squid and octopus).


Primitive ichthyosaurs were not well streamlined. There was an evolutionary trend within this group towards greater streamlining. This would have allowed them to swim faster and hunt fish more actively.


Temnodontosaurus. 3D specimen of juvenile found in Charmouth, Dorset

More advanced ichthyosaurs resemble modern dolphins and tuna in their morphology, and this may be because their type of body form is the most well-adapted for the swift pursuit of fish.

Advanced ichthyosaurs had incredibly large eyes relative to their body size, and it likely that they relied primarily on vision rather than smell for hunting.

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Author: Rachel Jennings
Last updated: 10/11/2005
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