Published: June 2009 River Spirits By Mark Jenkins    The Amazon
dolphin, Inia geoffrensis, parted company with its oceanic
ancestors about 15 million years ago, during the Miocene epoch.
Sea levels were higher then, says biologist Healy Hamilton of
the California Academy of Sciences in San Francisco, and large
parts of South America, including the Amazon Basin, may have
been flooded by shallow, more or less brackish water. When this
inland sea retreated, Hamilton hypothesizes, the Amazon dolphins
remained in the river basin, evolving into striking creatures
that bear little resemblance to our beloved Flipper. These
dolphins have fat, bulbous foreheads and skinny, elongated beaks
suited to snatching fish from a tangle of branches or to rooting
around in river mud for crustaceans. Unlike marine dolphins,
they have unfused neck vertebrae that allow them to bend at up
to a 90-degree angle—ideal for slithering through trees. They
also have broad flippers, a reduced dorsal fin (a larger one
would just get in the w