Known as the "Goddess of the Yangtze", what type of marine mammal is a Baiji?

The baiji is a possibly extinct species of freshwater dolphin native to the Yangtze river system in China. It is thought to be the first dolphin species driven to extinction due to the impact of humans. This dolphin is listed as “critically endangered: possibly extinct” by the IUCN (International Union for Conservation of Nature), has not been seen in 20 years, and several surveys of the Yangtze have failed to find it.

In China, the species is also called the Chinese river dolphin, Yangtze river dolphin, Yangtze dolphin and whitefin dolphin. Nicknamed the "Goddess of the Yangtze", it was regarded as the goddess of protection by local fishermen and boatmen. It is not to be confused with the Chinese white dolphin (Sousa chinensis) or the finless porpoise.

Baiji were thought to breed in the first half of the year, the peak calving season being from February to April. Gestation would last 10–11 months, delivering one calf at a time; the interbirth interval was 2 years. Calves measured around 80–90 centimetres (31–35 in) at birth, and nursed for 8–20 months.

Males reached sexual maturity at age four, females at age six. Mature males were about 2.3 metres (7 ft 7 in) (7.5 ft) long, females 2.5 metres (8 ft 2 in), the longest specimen 2.7 metres (8 ft 10 in). The animal weighed 135–230 kilograms (298–507 lb), with a lifespan estimated at 24 years in the wild.