Researchers have discovered a new species of giant tortoises on the island of Santa Cruz in the centre of the Galapagos Archipelago.

There are two populations of giant tortoises on the island -- a large population on the west side in an area known as the "Reserve" and another on the lower eastern slopes around a hill named "Cerro Fatal."

Until the recent discovery, researchers believed that these populations belonged to the same species of tortoise.

Genetic and morphological analyses conducted by an international group led by Gisella Caccone of Yale University in the US have now clearly identified the two populations as separate species: the Western Santa Cruz Tortoise (Chelonoidis porteri) and the new Eastern Santa Cruz Tortoise.

The discovery of the new species is likely to help focus attention on the newly named Eastern Santa Cruz Tortoise (Chelonoidis donfaustoi), said one of the researchers James Gibbs, conservation biologist at the State University of New York.

"This is a small and isolated group of tortoises that never attracted much attention from biologists previously," Gibbs said.

"But we now know that they are as distinct as any species of tortoise in the archipelago. Their discovery and formal description will help these tortoises receive the scientific and management attention they need to fully recover," Gibbs noted.

Giant tortoises have been among the most devastated of all Galapagos creatures because of human exploitation, introduced species and habitat degradation, the researchers pointed out.

The discovery was detailed in a study reported in the journal PLOS ONE.