Size and Weight:
About the Baiji:
The Baiji--also known as the Chinese River Dolphin, the Yangtze River Dolphin and (less frequently) by its species name, Lipotes vexilifer--occupies that unfortunate interval between a dwindling number of sightings and "functional extinction." This graceful, moderately sized, freshwater dolphin once occupied a thousand-mile stretch of China's Yangtze river, but it hasn't exactly flourished in modern times; as long ago as 300 B.C., early Chinese naturalists counted only a few thousand specimens. If the Baiji was imperiled back then, you can imagine the reasons it has completely disappeared today, with over 10 percent of the world's population lining the shores (and exploiting the resources) of the Yangtze River.
Like a patient dying of a terminal disease, extraordinary efforts were made to resuscitate the Baiji when people realized it was about to go extinct. In the late 1970's, the Chinese government established reserves along the Yangtze River for the Baiji, but most individuals died shortly after being relocated; even today, authorities maintain no less than five Baiji reserves, but there have been no confirmed sightings since 2007. It may yet prove possible to reintroduce the Baiji by breeding captive individuals, a program known as de-extinction, but it's more likely that the very last Baiji will die in captivity (as has happened with many other recently extinct animals, such as the Passenger Pigeon and the Quagga).