La Gomera giant lizard
Rediscovered in 1999, although there are only about 200 of them alive today. As they are quite intelligent lizards, they have the ability to avoid detection for decades so fear not, really.
Madagascar Serpent Eagles
Believed extinct as they were unseen for over 60 years. However it was back in 1993 that Russell Thorstrom rediscovered them. currently, there are only less than 1,000 Madagascar Serpent Eagles which exist today.