<p>Amazon dolphins (Inia geoffrensis) bear little resemblance to our beloved Flipper. How'd they get to the Amazon—and why are the males pink?</p>

Amazon dolphins (Inia geoffrensis) bear little resemblance to our beloved Flipper. How'd they get to the Amazon—and why are the males pink?

River Spirits

Tracking prey deep in the forest, freshwater dolphins make the most of the Amazon’s prodigious annual flood.

The dolphins are swimming through the trees. Bending sinuous bodies, they glide through branches and curl like snakes around fluted trunks. As frog-green fish dart through the leaves, the dolphins, pink as bubble gum, snap at them with long, toothy beaks.

This is not some kaleidoscopic dreamscape from a novel by Gabriel García Márquez; this is the wet season in the upper Amazon, downstream from Iquitos, Peru. The river has flooded the rain forest, luring freshwater dolphins to hunt in the woods.

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 way in tight spots), and small eyes—echolocation helps them pinpoint prey in muddy water.

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