Image caption Formal delineation of dolphin species is notoriously tricky

Researchers have determined that dolphins found in southeastern Australia represent a previously unknown species.

Around 150 of the dolphins live around the Melbourne area and had until now been assumed to be one of the known bottlenose dolphins.

But detailed DNA studies and analysis of skulls in museums showed the two populations are in fact a new species.

The new classification as Tursiops australis is described in PLoS One.

The common name of Burrunan dolphins derives from the Aboriginal Australian for "large sea fish of the porpoise kind".

Previous research had shown that the DNA found in the dolphins differed from that of the known bottlenose species Tursiops truncatus and Tursiops aduncus.

But in order to define a new species, more evidence is needed. Kate Charlton-Robb of Monash University in Melbourne and her colleagues studied dolphin skulls found in a number of museums, as well as more detailed analysis of DNA, to show that T. australis is clearly a different animal.

"This is an incredibly fascinating discovery as there have only been three new dolphin species formally described and recognised since the late 1800s," Ms Charlton-Robb said.

"What makes this even more exciting is this dolphin species has been living right under our noses, with only two known resident populations living in Port Phillip Bay and the Gippsland Lakes in Victoria state."

In fact, now that it is recognised as a separate species it may immediately qualify under Australia's criteria for endangered animals.

"The formal recognition of this new species is of great importance to correctly manage and protect this species, and has significant bearing on the prioritisation of conservation efforts," the authors wrote.

"This is especially crucial given its endemism to a small region of the world, with only two small known resident populations."