Arenaerpeton supinatus is the fourth species of chigutisaurid temnospondyl amphibian from Australia and the first from the Sydney Basin.
Arenaerpeton supinatus lived approximately 248 million years ago on the ancient supercontinent Gondwana.
The ancient creature was 94 cm long (excluding the tail) and had a large number of small marginal teeth.
The animal was a member of Chigutisauridae, an extinct family of large temnospondyl amphibians that became widely distributed on Gondwana.
“Chigutisauridae is a family of brachyopoid temnospondyl amphibians with the longest temporal range of all temnospondyl families spanning the Lower Triassic through to the Lower Cretaceous,” said Dr. Lachlan J. Hart, a paleontologist at the University of New South Wales and the Australian Museum Research Institute, and colleagues.
“Chigutisaurids are only known from Gondwana, with fossils recorded from Argentina, Australia, Brazil, India, and South Africa.”
The articulated skeleton of Arenaerpeton supinatus, containing cranial and postcranial elements, was found in Kincumber Quarry, on the Central Coast of New South Wales, approximately 90 km north of Sydney, Australia.
The fossil was preserved in sandstone from within the Terrigal Formation of the Lower-Middle Triassic Sydney Basin.
“The holotype was found among rocks intended for construction of a garden retaining wall at a private property in the mid-1990s,” the paleontologists explained.
“It was subsequently donated to the Australian Museum but has not received a formal description until the present paper.”
Arenaerpeton supinatus is the fourth named chigutisaurid species from the Australian continent, joining Keratobrachyops australis from the Lower Triassic, Siderops kehli from the Lower Jurassic, and Koolasuchus cleelandi from the Lower Cretaceous.
“Arenaerpeton supinatus is also only the second chigutisaurid from the Early Triassic and adds weight to the observations on the asymmetric distributions of brachyopoids throughout the Mesozoic,” the researchers said.
“Chigutisauridae is strictly a Gondwanan clade which has no records in the Middle Triassic, although constituent species have a temporal span from the Early Triassic through to the Early Cretaceous.”
“However, brachyopids are known throughout the Middle Triassic in Gondwana.”
“Chigutisaurids and brachyopids only co-occur in two localities, both in Australia: Arenaerpeton supinatus with Platycepsion wilkinsoni; and Keratobrachyops australis with Xenobrachyops allos.”
“Apart from these two occurrences, brachyopids, chigutisaurids (and plagiosaurids, also a brachycephalic clade) show marked differentiation in their distribution.”
“This may indicate that an ecological (perhaps an ability to estivate or tolerate unfavorable climatic conditions) or morphological trait (such as overall large body size, or skull shape) drove this segregation, and possibly also assisted chigutisaurids in their survival through to the Cretaceous period.”
The team’s work was published this month in the Journal of Vertebrate Paleontology.
Lachlan J. Hart et al. A new chigutisaurid (Brachyopoidea, Temnospondyli) with soft tissue preservation from the Triassic Sydney Basin, New South Wales, Australia. Journal of Vertebrate Paleontology, published online August 3, 2023; doi: 10.1080/02724634.2023.2232829