The problem with declaring a species extinct is that they are often not. In 2004 the IUCN listed Adenomus kandianus, a Sri Lankan bufonid, as extinct because it has not been recorded for over 100 years, and field work during the previous decade failed to find the toad.
Adenomus kandianus Günther (1872) was previously known only from two specimens in the British Museum. The species is endemic to Sri Lanka, and the original description gave the type locality as "Ceylon" (= Sri Lanka). The epithet suggests that it might have been collected in the vicinity of the city of Kandy, central Sri Lanka. The Kandy Toad was known only from the type specimen and one syntype until Mendis et al. (2012} reported its rediscovery.
Claims that small animals are extinct are always problematic given that populations may exist outside of the known range, the ability of many animals to enter stasis for long periods of time, and that often the animals are difficult to distinguish from their close relatives.
Citation
L. J. MENDIS WICKRAMASINGHE, DULAN RANGA VIDANAPATHIRANA & NETHU WICKRAMASINGHE (Sri Lanka): Back from the dead: The world’s rarest toad Adenomus kandianus rediscovered in Sri Lanka Zootaxa 3347: 63–68.