A Fish Which Stayed in the Water 

A correspondent sent me THIS LINK which describes an early tetrapod (from which we are descended) which could have ventured on land but decided to stay in the water.

The fossil was found on Ellesmere Island in the Canadian Arctic. CT scanning was used to see inside the rock, and to the surprise of the investigators it revealed a fin. They had already determined that they were looking at a tetrapod. Instead of finding fingers and toes they had a fishy fin!

They surmise that the beastie had turned back from the waters edge and evolved to live, once again, in open water. 

This shows that evolution is not a one way street - evolution is a reaction to local pressures.

An animation of the pectoral fin of Qikiqtania showing how it was preserved in the rock. Scales are shown in yellow, fin rays in blue, and the endoskeleton in grey. Credit: Tom Stewart