New York, Jul 15 (IANS): The largest island in the Philippines may be home to the greatest concentration of mammal diversity in the world, say researchers who have been exploring the island for the past 15 years.

Their research, published in the scientific journal Frontiers of Biogeography, showed that 56 species of non-flying mammals are now known to live on the island, 52 of which cannot be found anywhere else in the world.

And out of those 56 species, 28 were discovered in the course of the team's research.

"It's become clear that Luzon Island has exceptional diversity and the greatest concentration of mammal diversity, I'd say on the planet," said one of the researchers Scott Steppan, Professor at Florida State University in the US.

Luzon is roughly 40,000 square miles and has never been connected to any continental land, but it has a complex geography.

It is tropical, but also very mountainous with lots of volcanic pieces that have come together as the continental plates have crunched into each other.

The mountaintops form distinct habitats that are widely different from the base of the mountain.

Combining the expertise of scientists from a variety of backgrounds, the team embarked on an extensive effort to catalogue the numerous species they believed were on this island.

Among the 28 new species discovered by the team, there are four species of tiny tree-mice with exceptionally long whiskers, and five species of mice that look like shrews and feed on earthworms.

"The fact that we found some new ones was not surprising," Steppan said. "New small mammals are being discovered all the time, but finding 28 new species on one island -- an island that had been studied pretty well before -- was beyond expectation," Steppan said.

For comparison, in Luzon there are 56 non-flying land mammals, 52 of which are endemic to the island.

In Cuba, which is roughly the same size, there are 15 total native non-flying mammals, most of which are native to the island, the researchers said.

"This revealed the exceptional diversity of Luzon," Steppan said.