Killer Whales May Be Two Distinct Species

Killer whales, also known as orcas, may be two distinct species, researchers have found. But most people have never seen anything beyond the standard Free Willy variety. The elusive second species, called Type D orcas, only live in the choppy, freezing waters off Antarctica, Wired reports.

The first record of Type D orcas dates back to 1955, when 17 of the odd-looking whales stranded on Paraparaumu Beach on New Zealand. Blunt, bulbous heads, tiny white eye spots, and delicate, curved dorsal fins made the orcas look unlike any others that had been observed. Scientists collected a skeleton and brought it to the Museum of New Zealand Te Papa Tongarewa in Wellington, where it’s been for almost 60 years.

For half a century, scientists didn’t know whether the stranded orcas were an example of strange mutations within a single family group, or a distinct type of killer whale.

In 2004, however, the evidence began to build. Photos of the strange whale began to emerge, taken from expeditions in various locations near Antarctica. In 2010, as cruise ships began to make more frequent trips to that southernmost continent, more people reported seeing the whales or produced images of them. Total sightings, Wired reports, now number around a dozen.

To figure out how the whales are related to the orca species that we know so well, researchers returned to the 1955 specimens, still preserved in New Zealand.

There, they extracted DNA from bone and soft tissue clinging to the skeleton from the 1955 stranding. They ground up the samples, releasing decades-old genetic material. From that pool emerged the whale’s mitochondrial DNA, small rings of no more than 17,000 base-pairs that live within the energy-producing organelles in cells. Unlike nuclear DNA, which is inherited from both parents, mitochondrial DNA is passed down through the maternal lineage; there is little to no recombination, and the sequence only changes when mutations occur.

The Type D whales’ DNA differed significantly from other orcas, the team found. The two orca types seemed to have split into distinct groups around 400,000 years ago.

The researchers aren’t certain whether the Type D orcas are a full blown separate species, however, or a sub-species (animals capable of interbreeding with the parent species) of common orcas. To make matters more complicated, the researchers told Wired that they estimate up to six or seven different species or sub-species of killer whales may live around the world.

More from Smithsonian.com:

What the Inuit Taught Scientists About Killer Whales
Rare Sighting of All-White Orca Whale

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.