Gray's Beaked Whale
The rare whales that washed up in New Zealand were initially identified as the more common Gray's beaked whale, pictured here. New Zealand Government

The ocean consistently yields up new species, as well as specimens of animals thought long extinct, like the coelacanth, a fish “rediscovered” in 1938. Now, researchers say that a rare whale has resurfaced in New Zealand.

The spade-toothed beaked whale, or mesoplodon traversii, is one of the world's rarest living mammals. It ranges across 53 million square miles of ocean in the South Pacific and is thought to be a gifted deep-sea diver, foraging for squid and spending scarce time at the surface.

Until now, all that scientists have known about the spade-toothed beaked whale was gleaned from just a few bones -- three partial skulls found in New Zealand and Chile, collected in 1872, the 1950s and 1986.

“It is remarkable that we know almost nothing about such a large mammal," University of Auckland biologist Rochelle Constantine said in a statement.

But Constantine and colleagues from the University of Auckland, Oregon State University and Museum of New Zealand Te Papa Tongarewa may have stumbled across complete specimens while investigating a case of mistaken whale identity. Two whales, a mother and a male calf, washed up on a New Zealand beach and died there in December 2010. They were initially identified by conservation officials as Gray's beaked whales.

But when the researchers conducted DNA testing as part of a program collecting data on New Zealand's beaked whales, they discovered that the sequences of these two specimens didn't match the profile of a Gray's beaked whale. Instead, the mother-son pair are actually specimens of the elusive spade-toothed beaked whale, Constantine and her colleagues said in a paper published in the journal Current Biology.

"This is the first time this species -- a whale over five meters [16 feet] in length -- has ever been seen as a complete specimen, and we were lucky enough to find two of them," Constantine said.

While the adult female specimen has some similarities to a Gray's beaked whale, the shape of the melon, a fatty organ in the head, is more prominent in the specimen, and the specimen's upper jaw is colored dark gray where a Gray's beaked whale would be white. The likely spade-toothed whale also has distinct eye patches, a white belly and dark flippers that distinguish it from the more common species, the authors say.

Rapid advances in DNA sequencing mean that more rare marine species will be “rediscovered” in the flesh in the future.

But how has the spade-toothed beaked whale remained so elusive?

"It may be that they are simply an offshore species that lives and dies in the deep ocean waters and only rarely wash ashore," Constantine says. "New Zealand is surrounded by massive oceans. There is a lot of marine life that remains unknown to us."

SOURCE: Thompson et al. “The world's rarest whale.” Current Biology 22: R905-R906, 5 November 2012.