what about the Imperial Woodpecker? Well I don't think it's classified as extinct but I have a strong feeling that there are still some around.

Caribbean Monk Seal

The problem with a seal being "hidden" is that it is an animal that spends a lot of time on the seashore, so unless there is a big, unvisited island with them all hiding out there, it's very unlikely.

How can they say Any fish is extinct?

Fish lay hundreds or thousands of eggs. Many do not have to hatch right away but can lie dormant for years before they are ready to hatch - even out of water. Fish and or fish eggs can hide from researchers in a body of water that covers 71 % of the earth's surface. Man has only explored 5 percent of the worlds oceans. "Experts" can never have any proof any fish species is extinct.

Slayer69, that giant sloth you speak of - is alive and well and is in my living room. I married it.