Scientists say a newly-identified species of giant tortoise in the Galapagos Islands has been hiding itself in plain sight for more than 100 years, only now revealed through a genetic analysis.

Two separate populations of tortoises living on opposite sides of the island of Santa Cruz so closely resemble each other, they were long-believed to be the same species, both Chelonoidis porteri, researchers say.

However, DNA analysis shows the separated populations, although they live a little more than 10 miles apart, are separate, distinct species, they report in the journal PLOS ONE.

The finding presented the scientists with a dilemma: One of the island's populations is obviously a new, previously-unidentified species — but which one?

"As different as they are genetically, it's not obvious to the eye," says James Gibbs, professor of vertebrate conservation biology at the State University of New York at Syracuse.

The researchers looked at older specimens in museum collections to determine which of island's populations should be considered the "new" species.

It turned out the population on the western side of Santa Cruz is the already-known Chelonoidis porteri, making the eastern tortoise a new species in need of a new name.

The researchers have dubbed the new tortoises Chelonoidis donfaustoi in honor of former Galapagos National Park ranger Fausto Llerena Sánchez, called Don Fausto by colleagues and friends.

Sánchez recently retired after 43 years with the park, where he managed the captive tortoise breeding program.

"This guy dedicated his life to them," says study leader Adalgisa Caccone, an evolutionary biologist at Yale University in New Haven, Conn. "All the other [tortoise] species are named by scientists for scientists or explorers, but no species has been named after a person from Ecuador."

The identification of Chelonoidis donfaustoi brings the number of known giant tortoise species in the Galapagos Islands to 12.

Experts say identifying the new species could be vital in conservation efforts aimed at the Santa Cruz tortoises, since there are only about 250 C. donfaustoi known to live on the island.

With the new identification, the island's C. porteri population, which lives in a restricted geographic range, has been reduced by 250 members.

"Now when they're going to manage these populations, they can manage them more effectively by having a better understanding of their evolutionary history and where the different species are," suggests James Parham, a biodiversity expert at California State University, Fullerton, who was not involved in the study.

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