A team of Australian scientists led by UNSW Sydney palaeontologist Lachlan Hart has calculated the body mass of two ancient amphibians.
From: UNSW Media/Australian Museum
November 21, 2022 -- 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 the School of Biological, Earth & Environmental Sciences at
UNSW Sydney, has assessed various methods of estimating the weight of these
unique extinct animals. The team’s study is published in Palaeontology.
“Estimating mass in extinct animals presents a challenge, because we
can’t just weigh them like we could with a living thing,” said Mr Hart. “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 as case
studies
Mr Hart said temnospondyls were “very strange animals”.
“Some grew to enormous sizes, six or seven metres long. They went through
a larval (tadpole) stage just like living amphibians. Some had very broad and
round heads – such as Australia’s Koolasuchus, recently named as
the Victorian State Fossil Emblem – and others, like the temnospondyls we used
in this study, had heads that were more croc-like.”
The 1.8 metre-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 more aquatically
inclined Paracyclotosaurus was the heftier of the two, tipping
the scales at roughly 260 kilograms, where Eryops was a more modest 160
kilograms.
“The size of an animal is important for many aspects of their life,” said
Mr Hart. “It impacts what they feed on, how they move and even how they handle
cold temperatures. So naturally, palaeontologists are interested in calculating
the body mass of extinct creatures so we can learn more about how they lived.
“There have been several studies on body mass estimation in other groups
of extinct animals, such as dinosaurs, but not extensively on temnospondyls.
“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,” Mr Hart said.
Because temnospondyls have no direct living relatives, the team of scientists
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 3-dimensional digital models of the animals,” said Dr. Nicolas
Campione from the University of New England, Armidale, an authority on body
mass estimation who was also involved in the study. “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.”
Dr. Matthew McCurry, Senior Lecturer in Earth Science at UNSW, and
co-author on the study said, “This work has shown 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 palaeontologists because many fossils we find are only of one or two
parts of the skeleton.”
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