The last of the temnospondyls, amphibians that look more like crocodiles, became extinct during the Cretaceous period, about 120 million years ago, after thriving on Earth for more than 200 million years.
Now, a team of scientists led by Lachlan Hart, a palaeontologist and PhD candidate in UNSW Sydney’s School of Biological, Earth and Environmental Sciences, has evaluated several methods to estimate the weight of these unique extinct animals . The team’s study is published in Paleontology.
“Estimating mass in extinct animals presents a challenge, because we can’t just weigh them like we could a living thing,” Hart said. “We only have fossils to tell us what an animal looked like, so we often have to look at living animals to get an idea of soft tissues, like fat and skin.”
Temnospondyls as case studies
Hart said temnospondyls were “very strange animals.”
“Some grew to enormous sizes, six or seven meters long. They went through a larval stage (tadpole) just like living amphibians. Some had very broad, round heads, such as Australia’s Koolasuchus, recently named the Victorian state fossil emblem, and others, such as the temnospondyls we used in this study, had more crocodile-like heads “.
3D models of the animals that appear in the study. Image by Lachlan Hart.
The 1.8 meter long Eryops megacephalus lived during the Permian period in what is now the USA, while the slightly longer Paracyclotosaurus davidi is known from the Triassic of Australia. The water-leaning Paracyclotosaurus was the heavier of the two, tipping the scales at about 260 kilograms, where Eryops weighed in at 160 kilograms more.
“An animal’s size is important to many aspects of its life,” Hart said. “It affects what they eat, how they move, and even how they handle cold temperatures. So, naturally, paleontologists are interested in calculating the body mass of extinct creatures so we can learn more about how they lived.
“There have been several studies of body mass estimation in other groups of extinct animals, such as dinosaurs, but not extensively on temnospondyls.
“They survived two of Earth’s five major mass extinction events, which makes them a very interesting case study of how animals adapted after these global catastrophes,” Hart said.
Because temnospondyls have no direct living relatives, the team of scientists had to gather a selection of five modern “analogues” (such as the Chinese giant salamander and the saltwater crocodile) to test a total of 19 different techniques of ‘body mass estimation to determine suitability. for use in temnospondyls.
“We found several methods that gave us consistently accurate body mass estimates in our five live animals, which included the use of mathematical equations and three-dimensional digital models of the animals,” said Dr. Nicolas Campione of the University of Nova Scotia. England, Armidale, an authority. on body mass estimation who also participated in the study. “We hypothesized that because these methods are accurate for animals that lived and looked like temnospondyls, they would also be suitable for use with temnospondyls.”
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Dr Matthew McCurry, Senior Lecturer in Earth Sciences at UNSW and co-author of the study said: “This work has shown that there are multiple methods for estimating mass in temnospondyls.
“We don’t need the whole skeleton to do this, as some methods involve using the width of the skull or the circumference of the legs. The work will be useful for paleontologists because many fossils we find are only one or two parts of the skeleton”.