A mother spade-toothed beaked whale -- the "rarest whale in the world" -- and her male calf have washed up on a beach in New Zealand. It's the first time that marine biologists have seen full specimens of the creature, despite knowing of its existence for 140 years.

The whales became stranded, and died, on Opape Beach on the northeast of New Zealand's North Island in December 2010, and were initially mistaken for two of the more common Gray's beaked whale. DNA results published in the 6 November issue of Current Biology, however, show that this initial assumption was a mistake.

It was a result nobody was expecting, because until now the only evidence for the spade-toothed beaked whale's existence has been a mere three partial skulls collected from beaches in New Zealand and Chile over the span of a century and a half. The two whales that washed up had samples of their DNA taken as part of a general programme the New Zealand Department of Conservation is running to identify the 13 already-known species of beaked whale which live in the oceans surrounding the country -- New Zealand's location and relative oceanic isolation mean that it has a high enough number of whales beaching every year to justify a systematic cataloguing policy. The results were only processed recently, however, hence the delay in the announcement.

The scarcity of beaked whales in particular may be down to their deep ocean habitats. Kirsten Thompson of the University of Auckland, lead author of the paper, writes: "[The South Pacific Ocean] is a massive and poorly surveyed habitat, [with] some of the deepest ocean trenches. Within this area are many rare deep-water species, including the enigmatic beaked whales. Very little is known of the life history of these cetaceans and whilst there are 21 recognised species, many are described from only a small number of records. Beaked whales are thought to be exceptionally deep divers, foraging for squid and small fish and spending little time at the surface."