Chinese river dolphin
The Chinese river dolphin (Lipotes vexillifer)  or baiji  was a river dolphin. It was found only in the Yangtze River in China.  The last confirmed sighting of the baiji was in 2004 but there were possible sightings in 2007 and 2016 as well. The baiji was declared functionally extinct in 2007.  that means experts said that even if there had been a few baiji left alive in 2007, there were probably not enough left to have young and keep the species alive. The IUCN Red List says the baiji is critically endangered but not really extinct.