<i>Cymbospondylus</i> was the first large ichthyosaur, growing to
ten meters long, about the size of an adult male killer whale.
This ichthyosaur was very elongate. It had 60 vertebrae in front of its pelvis and
its very long tail would have assisted in propulsion.
<i>Cymbospondylus</i> also had a much longer snout then earlier ichthyopterygians.
It also has the smallest orbit and therefore eye of any known ichthyosaur.
<i>Mixosaurus</i> represents further steps towards solving the aquatic problem.
Instead of a lizard-like body with a paddle-like tail,
it had a more fusiform, streamlined body, a small dorsal fin for
stability, and a lower tail fluke for added propulsion.
The amphicoelous shape of the vertebrae gave greater flexibility
to the spine and probably resulted in an anguilliform swimming
style similar to more primitive ichthyopterygians.
The biggest ichthyosaur of them all has been found in British Columbia and
is named <i><b>Shonisaurus</b></i>.
It was at least 21 meters long, which is about the size of a finned whale.
The skull alone would have been over three meters long.
<i>Shonisaurus</i> and other large ichthyosaurs known as shastasaurids
may or may not have had dorsal fins.
But paleontologists think they likely did have
a low tail fluke to generate additional thrust.
the vertebrae in this group had developed into the disc-like morphology
characteristic of the derived ichthyosaurs.
And they also lacked teeth as adults, and so what they ate is a mystery.
Some paleontologists think they may have swallowed soft-bodied cephalopods whole.