This Tiny Frog Is The World's Smallest Vertebrate
January 12, 2012

This Tiny Frog Is The World’s Smallest Vertebrate

A frog species -- discovered in Papua New Guinea by US researchers -- that is less than half the size of a US dime, has been named the world´s smallest vertebrate species, smaller than a fish that won the honor in 2006.

The frog, Paedophryne amauensis, which is about 7mm (0.27 in) long, was given the distinction of world´s smallest animal with a spine in Wednesday´s PLoS One journal. The researchers, led by Chris Austin of Louisiana State University made the discovery, along with another, slightly larger relative, Paedophryne swiftorum.

Austin and a team of scientists from the US, including LSU graduate student Eric Rittmeyer, made the discovery during a three-month long expedition to New Guinea, the world´s largest and tallest tropical island.

Austin and his colleagues suggest that the frog´s tiny stature is linked to its habitat, which is leaf litter on the forest floor. But finding these tiny critters was no easy task.

“It was particularly difficult to locate Paedophryne amauensis due to its diminutive size and the males´ high pitched insect-like mating call,” said Austin. “But it´s a great find. New Guinea is a hotspot of biodiversity, and everything new we discover there adds another layer to our overall understanding of how biodiversity is generated and maintained.”

Despite the new frog species´ claim, another researcher, Theodore Pietsch, an ichthyologist from University of Washington, told The Telegraph that the males of a species of deep-sea anglerfish are about 2mm smaller than this new frog species. Pietsch, who described the fish species in 2006, said the males do not have stomachs and live as parasites on the 1.8-inch-long females.

Steven J. Beaupre, a University of Arkansas scientist and president-elect of the American Society of Ichthyologists and Herpetologists, said many vertebrates have males and females of very different sizes, “so it is reasonable that the world´s smallest vertebrate may end up being either the males or the females of some specific fish or amphibian species.”

“The discovery of two new frog species comes as great news against the background of more prevalent accounts of tropical amphibian extinction,” Beaupre told the Telegraph in an email.

Knowing about such tiny creatures and their ecology helps scientists “better understand the advantages and disadvantages of extreme small size and how such extremes evolve,” said Beaupre. “Fundamentally, these tiny vertebrates provide a window on the principles that constrain animal design.”

“The size limit of vertebrates, or creatures with backbones, is of considerable interest to biologists because little is understood about the functional constraints that come with extreme body size, whether large or small,” said Austin.

There are more than 60,000 vertebrates known, with the largest being the blue whale at more than 75 feet long, and the smallest previously being a small Indonesian fish averaging 8mm long. It was originally believed by some that extreme size in vertebrates might be associated with aquatic species, as perhaps buoyancy offers support and facilitates the development of extremism. However, the two new frog species described are both terrestrial, suggesting that living in water is not necessary for small body size.

“We now believe that these creatures aren´t just biological oddities, but instead represent a previously undocumented ecological guild — they occupy a habitat niche that no other vertebrate does,” added Austin.

“We realized these frogs were probably doing something incredibly different from what normal frogs do — invading this open niche of wet leaf litter that is full of really tiny insects that other frogs and possibly other creatures weren´t eating,”  Austin said.

“The New Guinea forests are incredibly loud at night; and we were trying to record frog calls in the forest, and we were curious as to what these other sounds were,” said Austin. “So we triangulated to where these calls were coming from, and looked through the leaf litter.”

Because it was at night, and the frogs were incredibly small, Austin and colleagues decided the easiest way to capture them were to grab up small piles of leaf litter and place them in plastic bags. “When we did so, we saw these incredibly tiny frogs hopping around,” Austin told BBC News.

Getting photos took some effort because the little frogs are quick and can leap 30 times their own length, Austin said. But after hopping around for a bit, they settled down long enough for a few close-up shots, he added.

Before the new tiniest vertebrate was found, the title of “world´s smallest frog” belonged to the Brazilian gold frog (Brachycephalus didactylus) and its slightly large Cuban relative, the Monte Iberia Eleuth (Eleutherodactylus iberia), both of which measure less than a centimeter (0.4 inches) long.

Austin, whose expedition was sponsored by the National Science Foundation, has estimated that his team has found 20 previously unknown species in New Guinea, which is a biological hot spot of diversity that scientists figure they have only described about 60 percent of all living things there.


Image Caption: Photograph of a paratype of Paedophryne amanuensis (LSUMZ 95004) on U.S. dime (diameter 17.91 mm). Credit: Rittmeyer EN, Allison A, Gründler MC, Thompson DK, Austin CC


On the Net: