The Type-D killer whale, a type of orca generally thought to have its distinct look because of a rare genetic mutation, may actually be an entirely separate species of the cetacean, according to a recent study published in the journal Polar Biology.
Type-D orcas, known to live in the Southern Ocean, are set apart from their Type-A, B and C peers by their notably small white eye patch, bulbous head and shorter-than-normal dorsal fin. Other types of orca have much larger white eye patches and streamlined bodies. The first known observation of a Type-D orca was in 1955 when a small pod of the creatures washed up on the shores of New Zealand. Since then, there have only been a handful of at-sea sightings of a Type-D orca.
The stranding of the pod of Type-D orcas in 1955 resulted in the collection of one skeleton from the creatures. More than half a century later, scientists gathered genetic material from the skeleton to map its genome.
"We were really fortunate that someone had foresight to collect this sample and save it, Phillip Morin, study co-author and marine biologist with the U.S. Southwest Fisheries Science Center in La Jolla, Calif., told National Geographic.
A complete mitochondrial DNA sequence of the Type-D orca was compared with genetic samples from 139 other killer whales from around the world. From that, the researchers estimated the Type-D orca split from other killer whales almost 400,000 years ago.
"This study provides the first genetic support of Type-D potentially being a distinct subspecies or species of killer whale," the researchers wrote in their paper.
Although more testing must be done before a definitive conclusion is reached.
"There's a lot more diversity out there than we even know about yet," said Morin. "We still haven't even begun to sample large parts of the world where killer whales exist."