The Sea Squirt
The sea squirt has a very simple brain which is used only to find a suitable spot to root itself for life. Once it's settled into a spot, it no longer needs the brain, so it eats it
The
kakapo - the world's heaviest parrot - is not only another flightless bird but it's also nocturnal. As one Researcher simplified the situation:
It was too fat to be able to fly.
It was too dumb to remember that it couldn't fly.
It would spread its wings and fall like a brick
Taken from
h2g2 - Weird Animals - Edited Entry