After 17 years of study, scientists have determined that humpback dolphins inhabiting the waters of northern Australia and New Guinea are unique and should be classified as a separate species: Sousa sahulensis (pictured). Informally called the Australian humpback dolphin, the newly recognized species joins three other close relatives in the Sousa genus: the Atlantic humpback dolphin (S. teuszii), the Indo-Pacific humpback dolphin (S. chinensis), and the Indian Ocean humpback dolphin (S. plumbea). S. sahulensis, whose name refers to the Sahul Shelf, an underwater geological feature that stretches between northern Australia and southern New Guinea, made its scientific debut online in Marine Mammal Science on 31 July. So what makes S. sahulensis unique? Most obviously, it has a lower dorsal fin than those of the Atlantic and Indian Ocean humpback dolphins. It is also dark gray in hue, with a darker gray cape over its back, whereas its closest humpback neighbor, the Indo-Pacific version, is distinctly white. The researchers do not know how many Australian humpback dolphins exist, but suspect that there are unlikely to be more than a few thousand—and that, like the other humpback dolphins, they are threatened by coastal development, ship strikes, and accidental and intentional killing by people.