Dolphin With Four Fins May Prove Terrestrial Origins
Richard A. Lovett
for National Geographic News
Japanese fishers have found an unusual bottlenose dolphin with an extra set of fins that could be an evolutionary throwback to the time when the marine mammals' ancient ancestors walked on land.
The dolphin was captured alive off the southwestern coast of Japan on October 28. It was then shipped to the nearby Taiji Whaling Museum for study (map of Japan).
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While environmentalists decry the town of Taiji's annual practice of dolphin fishing and capture, this particular catch appears to be a genuine scientific find.
"This is an unprecedented discovery," Seiji Osumi of Tokyo's Institute of Cetacean Research said in a weekend press conference.
"I believe the fins may be remains from a time when dolphins' ancient ancestors lived on land," Osumi told reporters.
Scott Baker, associate director of the marine mammal program at Oregon State University in Corvallis, agreed, saying that "this certainly is direct evidence of evolution."
Dolphins normally have two fins that are structurally similar to other mammals' arms or front legs. But the recently discovered dolphin also has a pair of stubbier, symmetrical fins near its tail.
"This is what you would call an atavistic trait"—a genetic trait that appears to be an evolutionary throwback—Baker told National Geographic News.
The dolphin's extra fins are "an ancestral characteristic that has reemerged for some reason," Baker said.
"Humans occasionally are born with excessive hair—the so-called werewolf gene—so we look more like our ancestral form shared with apes."