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