Tiny frog hops over fish to become world’s smallest vertebrate

It’s only the size of a housefly, but this critter doesn’t take to the air on wings — it hops.

TORONTO — It’s only the size of a housefly, but this critter doesn’t take to the air on wings — it hops.

The unimaginably tiny frog, averaging just 7.7 millimetres from snout to butt, has now earned the distinction of being the smallest vertebrate in the world.

Named after the Amau River in Papua New Guinea where it was discovered, Paedophryne amauensis has a mighty voice for its size, says one of the biologists who unearthed the diminutive amphibian during a three-month expedition in 2009.

“It does not sound like a frog, it sounds like an insect,” Christopher Austin of Louisiana State University said in a telephone interview from Baton Rouge. “And it’s these . . . single notes that continuously come out of the frog, like tink, tink, tink, tink, tink, but really high-pitched.”

Hearing that repetitive mating call amidst the cacophony of sound made by various creatures in the nighttime tropical forest drew Austin and his post-doc student Eric Rittmeyer like iron filings to a magnet.

“For some reason, we decided to try to find out what was making this call. And there were lots of them calling in this one area,” recalled Austin. “I think biologists by nature are sort of curious individuals and I think that’s what sort of drives us into science, to answer questions.”

Using their two sets of ears, the pair was able to roughly triangulate the location from which the call was being emitted, an area on the forest floor made up of deep, moist leaf litter.

With darkness all around them, the scientists began peeling through the layers of leaf litter, looking for the source of the insect-like chirp. After repeatedly turning up nothing, they scooped up a big handful of leaves, deposited it in a clear plastic bag and took it back to their camp.

Leaning over the bag illuminated by head lamps, they doggedly went through its contents “leaf by leaf by leaf. And there were hundreds of leaves in that bag,” said Austin, head curator of amphibians and reptiles at the university’s Museum of Natural Science.

“And eventually I picked up one leaf and this tiny thing hopped off that leaf, and I didn’t even think it was a frog because it was so tiny,” he said of the animal, its brown body adorned with black splotches and a scattering of minute blazing sky-blue spots.

“At first I didn’t believe that frog was the frog that was making the call … A single male might call for a minute or so, then stop for a minute and start calling again for a minute … they can sustain it for so long. It goes on for hours.”

Their reaction when they discovered the miniature hopper was something like: “Holy cow.” Austin said.

“They’re also incredible jumpers,” he said, noting that the puny frog can leap a distance about 30 times its body length — or 25 centimetres (10 inches). To put that in perspective, that would be the same as a six-foot man leaping a distance of 54 metres (180 feet).

“Presumably that’s to avoid predation by other large invertebrates in the leaf litter,” such as scorpions, said Austin, who describes the discovery in the journal PLoS One on Wednesday.

For those who might be wondering, P. amauensis took over top spot on the smallest-vertebrate-in-the-world list from the Indonesian fish P. progenetica, which ranges in size from 7.9 to 10.3 mm.

And at the other end of the size scale? The mighty blue whale, Balaenoptera musculus, which can be grow to more than 25 metres long and tip the scales at 200 tons.