Where can I find information about animals which were thought to be extinct but were discovered not to be?

Question

i am mostly interested in mammals, fish and reptiles.
one i can name is the ceolocanth

Answer 1

They're called living fossils. The four most famous are the lungfish, the horseshoe crab, the lampshell, and the above-mentioned coelacanth. You should be able to find more by searching for 'living fossil.'