The award for the tiniest four-legged beast in the Northern Hemisphere goes to a dime-size Cuban frog, two biologists report.
Scientist Alberto Estrada found the new frog species hidden among leaves and ferns on Monte Iberia, a peak in eastern Cuba. At 10 millimeters long - less than half an inch - the new species is just a hair shorter from stem to stern than its nearest relative, the resident of a neighboring Cuban mount.But the new species isn't smaller than Psyllophryne didactlya, a frog that lives in Brazil's Atlantic coastal forest and holds the title for world's smallest tetrapod, or four-legged vertebrate. Males of that variety are a nose shorter than the new Cuban species, measuring 8.5 to 9 millimeters on average.
Finding the Northern Hemisphere's smallest frog illustrates the incredible diversity of the Caribbean forests, biologist S. Blair Hedges said. It also illustrates a fundamental ecological principle: Since Darwin's days, scientists have noticed that islands often are home to both oversize and miniaturized beasts.
"You see these records for the smallest and the largest occurring quite frequently on islands," said Hedges, an assistant professor at Pennsylvania State University.
He and Estrada, a herpetologist with Cuba's forest service, describe the new frog species in the December issue of the scientific journal Copeia. They can't reveal the name they've chosen for the frog yet, because taxonomic rules require that it come out in the journal first. But it's safe to say the name has to do with the geographic location where the frog was found.
Hedges noted that the world's smallest bird species, the bee hummingbird, also lives on Cuba. At the other end of the scale, there once was a bear-size rodent living on nearby Anguilla, but European settlers rendered it extinct. Along similar lines, a shrew the size of a cat once inhabited Cuba and Hispaniola.
Islands often host odd-size creatures because they're usually inhabited by a less diverse set of species than continents, Hedges said. So island animals often grow or shrink to fill ecological roles that otherwise would be filled by entirely different species.
Thus the tiny frogs of Cuba could be sitting in, ecologically speaking, for an insect or some other tiny animal that never crossed from mainland North America.
"It may not be a frog niche that this little guy is filling," Hedges said.
That explanation may work fine in Cuba, but it doesn't explain the tiny-title-holding frog of Brazil, said Ronald Heyer, a herpetologist at the Smithsonian Institution in Washington.
He speculated that the frogs there shrank to make themselves less conspicuous among the leaves and litter of the forest floor.
"They can hide in incredibly small crevices," Heyer said.