In the waters off the eastern coast of Australia, marine scientists report a first: 57 cases in which two species of shark are interbreeding. The local Australian black-tip shark is mating with its global counterpart, the common black-tip. They're similar, but they are distinct species.

"It's very surprising because no one's ever seen shark hybrids before," said Jess Morgan of the University of Queensland, the lead researcher, as quoted by AFP. "This is not a common occurrence by any stretch of the imagination."

Why would this happen? Why would two shark species hybridize after apparently keeping to themselves before? Morgan, whose team published its findings in the journal Conservation Genetics, said she thinks a change in climate may be part of it.

"If it [the Australian black-tip species] hybridises with the common species it can effectively shift its range further south into cooler waters, so the effect of this hybridising is a range expansion," Morgan said. "It's enabled a species restricted to the tropics to move into temperate waters."

Morgan confirmed the cross-breeding through DNA analysis.

Jennifer Ovenden of the Queensland Department of Primary Industries and Fisheries, who was a co-author of the Conservation Genetics paper, was quoted by News.com.au: "Hybridization could enable the sharks to adapt to environmental change as the smaller Australian black tip currently favors tropical waters in the north while the larger common black tip is more abundant in sub-tropical and temperate waters along the south-eastern Australian coastline."

The 57 hybrid sharks were found along a stretch of coastline about 1,250 miles long. Mixing the two species would presumably make them stronger, better able to withstand variations in their environment, said Morgan. "You're seeing evolution in action."