When most dolphins and porpoises are born, their tails come out first — an evolutionary adaptation that helps prevent newborns from drowning during delivery.

That's why researchers were surprised, and a little nervous, when a Yangtze finless porpoise calf nicknamed "Little 26" was born head-first last month at the Chinese Academy of Sciences' Institute of Hydrobiology in Wuhan.Scientists say the rare birth could offer new insights into the reproduction of the endangered species.

The Yangtze finless porpoise is China's only freshwater cetacean still surviving in the wild, after the baiji, or Yangtze river dolphin, was declared functionally extinct in 2006. China's decades-long efforts to protect the species, including a 10-year fishing ban on the Yangtze River, have shown encouraging results. Recent surveys have recorded a resurgence in the wild population after decades of decline.