Scientists expressed "surprise and delight" Thursday after a new humpback dolphin species was identified off northern Australia, with genetic mapping singling out an animal not previously known to science.
A global team led by the US-based Wildlife Conservation Society made the discovery after examining almost 200 dead dolphins and tissue specimens from live animals across the four Atlantic, Indian and Indo-Pacific ocean areas where humpbacks are known to live.
A study of the beak length and number of teeth in 180 skulls from beached and museum specimens, as well as live DNA samples from 235 dolphins, identified a new species in the humpback, or sousa genus, which frequents waters off northern Australia.
"Based on our combined genetic and morphological analyses, there is convincing evidence for at least four species within the genus," lead author Martin Mendez wrote in the paper, published in the latest edition of the journal Molecular Ecology, adding that this included "a new as-yet-unnamed species off northern Australia".
Biologist Guido Parra, a member of the study team from Australia's Flinders University, said it had long been debated that local humpbacks were distinct from their more distant cousins but there had been insufficient evidence until now to support the hypothesis.
"The unique thing about this study is that in previous debates the data sets were always limited -- either purely genetic or based on traditional taxonomic studies," Parra told AFP.
"We were able to actually marry those two -- so morphological and genetic -- and not only marry those two approaches but also look across the entire (genus) range.
"We are very surprised and of course delighted to discover the recognition of a completely new species."
Humpback dolphins have a vast home range stretching from the tip of Australia all the way to Africa, and they are considered native to some 40 countries across Asia, Africa and the Pacific.
Parra gathered skin biopsy samples from both deceased and live humpbacks off northern Australia for the study, which he said was a "long-term collaborative global project".
The Wildlife Conservation Society said it was a significant finding -- identifying a new mammal species is rare -- and that it hoped it would boost conservation efforts.
Two of the three already-identified sousa species are in decline and considered at risk from habitat loss and fishing, with S. chinensis, or Chinese white dolphin, found in the eastern Indian and West Pacific Oceans, listed as near-threatened by the International Union for Conservation of Nature.
S. teuszii, which lives in the Atlantic off West Africa and is known as the Atlantic humpback or Teusz's dolphin, is rated vulnerable.
The next step in the process would be to draw up a manuscript of the findings for consideration by the International Commission on Zoological Nomenclature, the body responsible for formally declaring and naming new species.
Parra said he could not reveal what potential names were being debated for the new humpback but said it would hopefully be "related to Australia".
It has been a bumper week for Australian scientists, with the discovery unveiled Monday of three new vertebrate species in a remote part of the country's north, isolated for millions of years and described as a "lost world".
Humpback dolphins are so named due to a distinctive hump just below their dorsal fin, which is also uniquely elongated.
Infant humpbacks are born a creamy or pearly white similar to a beluga whale and darken to grey as they reach adulthood. They typically grow to eight feet (2.4 metres) in length and live in coastal waters, deltas and estuaries.