Washington - The world's rarest whale - previously known only though bones - has been spotted in New Zealand where a mother and her male calf were examined, Current Biology reports.

The spade-toothed whale, or Mesoplodon traversii, previously had not been seen in the flesh, was known only from bone samples and it was not clear if the species was extinct or not.

“This is the first time this species - a whale over five meters in length - has ever been seen as a complete specimen, and we were lucky enough to find two of them,” said Rochelle Constantine of the University of Auckland.

“Up until now, all we have known about the spade-toothed beaked whale was from three partial skulls collected from New Zealand and Chile over a 140-year period. It is remarkable that we know almost nothing about such a large mammal,” she said.

The whales were found stranded on Opape beach in New Zealand in December 2010, the report explains. At the time, officials examined the whales and took tissue samples.

The whales were then identified not as spade-toothed beaked whales but as common Gray's beaked whales. Then later DNA testing show they were in fact the rarest of birds, whalewise.

It's not clear why the species - identified by bones found in 1872 - has remained so elusive to humans.

“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 said. “New Zealand is surrounded by massive oceans. There is a lot of marine life that remains unknown to us.” - Sapa-AFP