The discovery came when scientists with the Wildlife Conservation Society (WCS) tried to settle a decades-old argument among marine mammal researchers.

"For many years, there's been this debate about the number of species of humpback dolphins," said Howard Rosenbaum, director of the WCS ocean giants program. Scientists have proposed everything from two to four species within the group’s genus Sousa.

But there was never enough good evidence supporting claims of more than two species, Rosenbaum said. So about ten years ago, the community decided that until they had more information, they'd recognize only two species—the Atlantic humpback dolphin and the Indo-Pacific humpback dolphin.

Rosenbaum and colleagues decided to revisit this old argument, and started collecting physical and genetic samples