The lost shark (Carcharhinus obsolerus), previously known as the false smalltail shark, is a very rare species of requiem shark (family Carcharhinidae). It is known only from the Western Central Pacific Ocean, in the southern South China Sea. Only three specimens of this species are known, found in Borneo, Vietnam, and Thailand, all of which are over 80 years old. The specimens were originally tentatively assigned as belonging to the smalltail shark (C. porosus), but a number of subtle morphometric differences revealed that they belonged to a new Carcharinus species, referred to as Carcharinus sp. A. It differs from other Carcharinus species by the relative position of the second dorsal and anal fins, as well as its low vertebral count.
As no individuals have been identified for over 80 years, C. obsolerus may be extinct. Like other members of the C. porosus subgroup, C. obsolerus likely had limited fecundity and lived in shallow waters that are easily accessed by fishermen, both of which put it at heavy risk of extinction from overfishing. However, the rediscovery of the Borneo shark (C. borneensis) in 2004 after a long period of no sightings has kept hopes for its possible survival.
- Harris, Mark; Kyne, Peter M.; White, William T. (2019-01-02). "Lost before found: A new species of whaler shark Carcharhinus obsolerus from the Western Central Pacific known only from historic records". PLOS ONE. 14 (1): e0209387. doi:10.1371/journal.pone.0209387. ISSN 1932-6203. PMC 6314596.
- Gabbatiss, Josh (4 January 2019). "New 'lost' shark species may already be extinct due to overfishing". The Independent. The Independent. Retrieved 7 January 2019.