While thinking of two completely different ideas I remembered the famous Einstein quote “Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”
...and I wondered...
What do fish actually have in common with trees?
Then I looked it up:
Some fish live in trees??
I looked a bit more into it and found that one specific fish, the Mangrove Killifish, has adapted to survive inside of rotting branches for several months of the year.
So for my question I had to ask: How far can one species adapt before it isn't considered part of the animal class(eg:mammals, birds, fish) it was before?