Permian-Triassic Crocodile-Like Amphibians Were as Heavy as Pygmy Hippos, Study Suggests

by johnsmith

Temnospondyli is a diverse group of extinct amphibians that flourished worldwide during the Carboniferous, Permian, and Triassic periods. The body mass of these extinct creatures is a key variable in inferring their ecological, physiological and biomechanical attributes. However, estimating their body mass has proven difficult because the group has no extant descendants. In new research, paleontologists from the University of New South Wales and the University of New England applied a wide range of body mass estimation techniques developed for tetrapods to two iconic species of temnospondyls: Paracyclotosaurus davidi and Eryops megacephalus.

An artist’s reconstruction of Eryops megacephalus (left) and Paracyclotosaurus davidi (right). Image credit: Josè Vitor Silva.

An artist’s reconstruction of Eryops megacephalus (left) and Paracyclotosaurus davidi (right). Image credit: Josè Vitor Silva.

“Estimating mass in extinct animals presents a challenge, because we can’t just weigh them like we could with a living thing,” said Lachlan Hart, a Ph.D. candidate at the University of New South Wales.

“We only have the fossils to tell us what an animal looked like, so we often need to look at living animals to get an idea about soft tissues, such as fat and skin.”

“Temnospondyls were ‘very strange animals.’ Some grew to enormous sizes, 6-7 m long.”

“They went through a larval (tadpole) stage just like living amphibians. Some had very broad and round heads — such as Australia’s Koolasuchus — and others, like the temnospondyls we used in this study, had heads that were more croc-like.”

In the study, Hart and colleagues focused on two temnospondyl species: the 1.8-m-long Eryops megacephalus and the slightly longer Paracyclotosaurus davidi.

The former lived during the Permian period in what is now the United States, while the latter is known from the Triassic of Australia.

“There have been several studies on body mass estimation in other groups of extinct animals, such as dinosaurs, but not extensively on temnospondyls,” Hart said.

“They survived two of Earth’s Big Five mass extinction events which makes them a very interesting case study on how animals adapted following these global catastrophes.”

Because temnospondyls have no direct living relatives, the paleontologists had to assemble a selection of five modern ‘analogues’ (such as the Chinese giant salamander and the saltwater crocodile) to test a total of 19 different body mass estimation techniques to determine their suitability for use in temnospondyls.

“We found several methods which gave us consistently accurate body mass estimations in our five living animals, which included using mathematical equations and 3D digital models of the animals,” explained Dr. Nicolas Campione, a paleontologist at the University of New England.

“We hypothesized that as these methods are accurate for animals which lived and looked like temnospondyls, they would also be appropriate for use with temnospondyls.”

The authors found that the more aquatically inclined Paracyclotosaurus davidi was the heftier of the two, tipping the scales at roughly 260 kg, where Eryops megacephalus was a more modest 160 kg.

“This work has shown there are multiple methods for estimating mass in temnospondyls,” said Dr. Matthew McCurry, a paleontologist at the University of New South Wales.

“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 of one or two parts of the skeleton.”

The results were published in the journal Palaeontology.


Lachlan J. Hart et al. On the estimation of body mass in temnospondyls: a case study using the large-bodied Eryops and Paracyclotosaurus. Palaeontology, published online November 20, 2022; doi: 10.1111/pala.12629

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