The researchers failed to spot any Yangtze river dolphins, also known as baijis, during an extensive six-week survey of the mammals' habitat.The BBC site has a video report on this story, including footage of the Baiji in graceful action.
The team, writing in Biology Letters journal, blamed unregulated fishing as the main reason behind their demise.
If confirmed, it would be the first extinction of a large vertebrate for over 50 years.
The World Conservation Union's Red List of Threaten Species currently classifies the creature as "critically endangered".
Also, here's an older report from earlier in the year...