The world's smallest lizard has been discovered on a tiny Caribbean island off the coast of the Dominican Republic. The newly discovered species not only ranks as the smallest lizard, but it also is the smallest of all 23,000 species of reptiles, birds, and mammals, according to a paper to be published in the December issue of the Caribbean Journal of Science by Blair Hedges, an evolutionary biologist at Penn State, and Richard Thomas, a biologist at the University of Puerto Rico.
So small it can curl up on a dime or stretch out on a quarter, a typical adult of the species, whose scientific name is "Sphaerodactylus ariasae," is only about 16 millimeters long, or about three quarters of an inch, from the tip of the snout to the base of the tail. It shares the title of "smallest" with another lizard species named Sphaerodactylus parthenopion, discovered in 1965 in the British Virgin Islands. Hedges and Thomas discovered small groups of the new species living in a sink hole and a cave in a partially destroyed forest on the remote island of Beata, which is part of the Jaragua National Park in the Dominican Republic.
"Our discovery illustrates that we still don't know everything about the Earth's species, even in areas that are very close to the United States," Hedges says. "The island home of this tiny lizard is closer to Miami than Miami is to Puerto Rico, and we did not even know the species existed, although the area has been studied by biologists for several hundred years." Hedges says the habitat that this species needs to survive is disappearing rapidly. "People are cutting down trees even within the national parks and, if they take the forest away, these lizards and other species will disappear."
Economic and law-enforcement difficulties are contributing to deforestation of the Caribbean forests, which are even more fragile and more threatened than those in the Amazon of South America because they are so small. "In the Caribbean, forests that used to cover all of the land now typically cover less than 5 percent--and they are being cut down at an increasing rate, mainly for subsistence farming and fuel," Hedges says. "Although there are laws against cutting down trees in the national parks, the enforcement of the laws is not enough to protect the forests, for a variety of reasons."
Hedges and Thomas went to the remote Isla Beata specifically with the goal of discovering previously unknown species that might be living there. "We tend to explore more rugged and hard-to-reach areas than other scientists," Hedges says.
The "smallest" and "largest" species of animals tend to be found on islands, the researchers say, because species can evolve there over time to fill ecological niches in the habitat left vacant by other organisms that never reached the remote locations. If a species of spider is missing from an island, for example, the lizards there might evolve into a very small species to "fill" the missing spider's ecological niche.
"Habitat destruction is the major threat to biodiversity throughout the world," says Hedges, who has studied Caribbean species for many years, and has long recognized it as a "hot spot" of threats to biodiversity. "The Caribbean is now widely recognized by conservationists and biologists as an ecological hot spot because it clearly is an area that has an unusually high percentage of endangered species that occur nowhere else in the world," Hedges says. "Most land species on Earth have evolved to live in forested regions, and now humans are destroying the forests--which is a big problem, especially on islands, where species have restricted ranges."
"It is hard to say whether this lizard is as small as a lizard can get, but you would think it probably is approaching that limit because it is the smallest of all 23,000 known species of reptiles, birds, and mammals," Hedges says. "The smaller an animal gets, the larger its surface area gets as a percentage of the volume or mass of its body. At some point, it gets to be physiologically impossible to get any smaller." For the lizard, which lives in a dry environment surrounded by comparatively moist leaf litter, the limiting factor is the danger of desiccation. "If we don't provide a moist environment when we collect them, they rapidly shrivel right up and die by evaporation from the proportionally large area of their surface," Hedges explains.
Hedges and Thomas named the new lizard in honor of Yvonne Arias, a champion of conservation efforts in the Dominican Republic. Arias is president of the organization known as Groupa Jaragua, a non-governmental organization set up specifically for preserving the biodiversity of the Jaragua National Park.
Hedges and Thomas have discovered and described more than 50 new species of amphibians and reptiles throughout the Caribbean, mostly for genetic and evolutionary studies. Finding them, collecting them, and naming them is a necessary first step for other types of research. Hedges says this exploration and discovery of new species also is critical for protecting biodiversity. "It is difficult to protect a species when you don't know it exists," he says.
This research was sponsored by the Biotic Surveys and Inventories program of the U. S. National Science Foundation.
High-resolution images of the lizard plus other images and information are available from a link on the web at http://www.science.psu.edu/alert/Hedges11-2001.htm.
Caribbean Journal of Science