The Ichthyosaurs and the whales have an interesting evolutionary theory as to their appearance in the sea! Both have to have started as an air breathing land creature, who decided to change their DNA and body plans by some unknown means, to be able to live in an environment fatal for land dwellers! Only the Ichthyosaurs left the sea and returned to the land, by some unknown means of modifying its DNA and body plans to live in an environment fatal for sea dwellers! The fossil evidence for this has to be seen to be believed! Take a tour of the Natural History Museum and test the evidence for yourself!