Many species have been assigned to this genus, sometimes on the
flimsiest of fossil evidence. The genus is said to have persisted in a variety of different forms
from the Early Jurassic Period to the Early Cretaceous Period, a time span covering more
than 80 million years. A 'typical' Ichthyosaurus was shaped like a fish or dolphin - making.'
it an example of 'convergent evolution'. This is when different organisms come to resemble
each other due to a similar habitat and/or lifestyle.