Two whales which died after becoming stranded in the Bay of Plenty were spade-toothed beaked whales, a rare species.
The female whale and male calf died on Opape Beach on New Year's Eve in 2010 and photos and tissue samples were taken.
Details of a study of the samples have been published in Current Biology by scientists from The University of Auckland.
Until now, the only evidence for the existence of Mesoplodon traversii came from three skull and jaw fragments found around New Zealand and Robinson Crusoe Island near Chile.
Dr Rochelle Constantine told Morning Report the whales were buried, but iwi allowed the carcasses to be exhumed and they are now at Te Papa Museum in Wellington.
She said the whales may have low numbers or live so far out in the ocean that they are not spotted, but it is incredible such a large animal has remained concealed for so long.