When we think of amphibians, the first image that often pops to mind is that of a tiny, green tree frog - not a giant crocodile-like creature weighing as much as a grizzly bear.
However, a group of Australian scientists have revealed this strange thought might be an accurate imagining; new research published today has found that two ancient amphibians from the temnospondyl family would have weighed about 160 kilograms and 260 kilograms respectively.
"Using just the fossils of the 1.8-metre-long Eryops megacephalus, and the slightly longer Paracyclotosaurus davidi, we were able to estimate how much they would have weighed back when they were roaming the Earth and sea before becoming extinct around 120 million years ago," says University of New England palaeontologist, Dr Nicolas Campione, who co-authored the study alongside University of New South Wales PhD candidate and palaeontologist Lachlan Hart (lead) and the Australian Museum's Dr Matthew McCurry.
To figure out the body mass of these extinct animals, the research team applied 19 different estimation methods to find the perfect fit for the project.
As there are no living relatives of temnospondyls, they did this by trialling techniques on similar animals that are around today, such as the Chinese Giant Salamander and the Saltwater Crocodile.
"What we found was that there were several methods that gave us consistently accurate body mass estimations in our five living animals, which included using mathematical equations and three-dimensional digital models of the animals," says Dr Campione.
Using just the fossils of the 1.8-metre-long Eryops megacephalus, and the slightly longer Paracyclotosaurus davidi, we were able to estimate how much they would have weighed back when they were roaming the Earth and sea before becoming extinct around 120 million years ago.
"We hypothesised that as these methods are accurate for animals which lived and looked like temnospondyls, they would also be appropriate for use with temnospondyls."
Through the combination of these methods, they were able to accurately calculate the estimated weights, which Mr Hart says paints a picture of how the ancient amphibians once lived.
"The size of an animal is important for many aspects of their life," he says. "It impacts what they feed on, how they move, and even how they handle cold temperatures.
"Temnospondyls survived two of Earth's 'Big 5' mass extinction events which makes them a very interesting case study on how animals adapted following these global catastrophes."
As the effective estimation methods only required parts of the skeleton, Dr McCurry, who is the Curator of Palaeontology at the Australian Museum, says the study will also open doors to future research on other temnospondyls.
"This work has shown that there are multiple methods for estimating mass in temnospondyls," he says. "We don't need the whole skeleton to do this, as some methods involve using the width of the skull or the circumference of leg bones. The work will be useful for palaeontologists because many fossils we find are only of one or two parts of the skeleton."
You can read the full paper that was published today in the journal Palaeontology here, and you can find out more about the work Dr Campione does at UNE on the Campione Palaeobiology Lab website.
