The findings might someday help rescuers test whether the lost cetaceans might be deaf before releasing them back into the wild.

And although it may well be too late for the Baiji, cetaceans receive more attention than less 'marketable' species, that are nonetheless, vital for a functioning ecosystem.

Experts agree that hippos belong to the mammalian order artiodactyla, a group of even - toed, hoofed creatures whose extant representatives include camels, pigs and ruminants such as cows.