This is a conceptual drawing of what Gerobatrachus hottoni, a.k.a. Froggie, might have looked like about 275 million years ago. The ancient amphibian could be the missing evolutionary link between modern-day frogs and salamanders. ((Michael Skrepnick/Canadian Press))

It likely spent its days on the edge of a quiet, brackish pond, lunging at mayflies for lunch and taking to the water to elude predators.

Part-frog, part-salamander, Gerbatrachus hottoni lived about 275 million years ago, and the only fossil of the creature ever found has shed new light on just how ancient amphibians evolved into these two separate species.

Canadian scientists who undertook the painstaking work of exposing and analyzing the fossilized remains of the prehistoric creature say that Gerbatrachus hottoni (Hotton's elder frog) is the missing link, the common ancestor that lived before frogs and salamanders hopped or walked down their separate evolutionary paths.

They say their research, published in Thursday's issue of the journal Nature, settles a long debate in scientific circles as to just how these species evolved.

"This fossil is the most like the modern amphibian that you find, and it's from incredibly ancient times," said principal investigator Jason Anderson, an assistant professor of veterinary anatomy at the University of Calgary who specializes in vertebrate paleontology.

"So what this does is provide conclusive evidence that frogs and salamanders have an origin among one particular group of extinct fossil amphibians," he said Wednesday from Calgary. "This fossil falls right into a gap in the fossil record between one archaic group of amphibians and the earliest examples of the modern amphibians, frogs and salamanders."

The fossilized remains were discovered in 1995 in the scrubland of north-central Texas by the late Nicholas Hotton of the Smithsonian Institution, the man for whom the long-extinct creature is named.

Hotton, who died two years later, knew he had made a significant find, said Anderson.

"With a slip of paper found with the specimen and in his handwriting is the nickname 'Froggie.' So he recognized the specimen for what it was immediately after he found it."

Fossil rediscovered at Smithsonian

The slab of silt stone bearing the 12-centimetre-long creature's imprint had languished in the Smithsonian's collection for some time before a U.S. colleague brought it to Anderson's attention; he jumped at the chance to create a team to partially raise it from its rocky grave.

Co-author Robert Reisz, a professor of biology who heads a vertebrate paleontology research lab at the University of Toronto, came on board to lay bare the creature's skeleton, delicately chipping away at the chalk-like rock in which it was embedded.

Working on the tiny teeth — less than one millimetre in size — was especially challenging, said Reisz.

"This is not an easy specimen to study," he said in an interview. "We don't extract [the fossilized skeleton] because it would fall apart; basically we expose."

Froggie, as it turned out, combined features of both frog and salamander.

"It's got a great big froggie ear and it's reduced the number of vertebrae in its back … but like salamanders, it shares a particular fusion of some ankle bones," said Anderson.

"The skull itself, you look at the skull and it is almost what you'd expect to see in a frog, really lightly built, kind of like soaring, flying buttresses on a cathedral, long arching struts, really broad and wide," he explained with undisguised enthusiasm.

"When I first saw the creature, I knew that this was close to the frog-salamander split … There's about 50 million years between this fossil and the very first frog fossil."

Anderson said the fossil dates to a period about 50 million years before the dinosaurs first walked the Earth.

The researchers believe the discovery is important not just for science, but also for the general public.

"This is an important stage in the evolution of life that exists on Earth today, and being able to understand that, knowing a little more of the history of how we got to where we are at present is deeply satisfying on a sort of intellectual level," said Anderson.

But it is also a reminder, in this the Year of the Frog (named by Amphibian Ark, an international organization dedicated to preserving amphibian diversity), that populations of frogs and related species worldwide are in severe decline due to a number of environmental factors, including global warming and loss of habitat.

"It's a potential global extinction," said Anderson, adding that humans and amphibians once shared a common ancestor deep in the mists of time.