Arenaerpeton supinatus
As a child growing up in the North Oxfordshire countryside, and already deeply interested in all things to do with nature, one of my favourite ways of looking for fossils was to search the many dry-stone walls used as field boundaries in the area. Being made largely from sedimentary limestone, they often contained fossils of ancient marine molluscs. It would probably have given a creationist nightmares to find evidence of vanished seas in a field wall, but even that is modest compared with a fossil discovered in a slab intended for use in a garden retaining wall in New South Wales, Australia.
The slab was among stones obtained in the 1990s from a local NSW quarry by a retired chicken farmer who intended to use them to build a garden retaining wall. When he spotted the fossil, however, he donated the slab to the Australian Museum in Sydney. Decades later, Australian Museum palaeontologist Lachlan J. Hart, with colleagues from the University of New South Wales and the University of Washington, Seattle, identified it as the 240-million-year-old fossil of Arenaerpeton supinatus. The fossil preserves most of the skeleton and, unusually, even shows the outline of the animal’s skin. Their formal description was published in the Journal of Vertebrate Paleontology.
Arenaerpeton supinatus, meaning ‘supine sand creeper’, inhabited freshwater rivers in what is now the Sydney Basin during the Triassic Period, around 240 million years ago. It may have been one of the top predators in that environment, hunting ancient fish such as Cleithrolepis. Superficially, it resembled the modern Chinese giant salamander, but it was more heavily built and armed with powerful teeth, including a pair of fang-like tusks in the roof of its mouth.
What Were The Temnospondyls? Temnospondyls were a highly diverse group of extinct early tetrapods, often described informally as “amphibians”, although they were not simply oversized versions of modern frogs, newts or salamanders. They first appeared in the Carboniferous, around 330 million years ago, and survived for more than 200 million years, through the Permian and Triassic and, in some places, into the Jurassic and Cretaceous.How the fossil was discovered and identified is explained in a UNSW news item:
They ranged from small, salamander-like forms to large, crocodile-like predators several metres long. Many were semi-aquatic or fully aquatic, living in rivers, lakes, swamps, lagoons and coastal environments, although some smaller forms were more terrestrial. The large aquatic species often had broad, flattened skulls, upward-facing eyes and powerful jaws, making them well suited to ambushing fish and other prey in shallow water.
The name “temnospondyl” refers to the structure of their vertebrae, which were composed of separate bony elements rather than the simpler vertebral structure seen in living amphibians and reptiles. Many also had heavily ornamented skull bones, large palatal openings, and teeth not only around the jaws but also on the roof of the mouth. In some forms, these roof-of-mouth teeth became fang-like tusks.
Temnospondyls were especially successful before dinosaurs became dominant. Some survived the end-Permian mass extinction, the most severe extinction event in the history of complex life, and continued as important aquatic predators during the Triassic. Arenaerpeton supinatus, from the Sydney Basin, belonged to this long-lived lineage and shows that temnospondyls were still thriving in Australian freshwater ecosystems around 240 million years ago.
Their relationship to living amphibians is still debated. Many palaeontologists think modern frogs, salamanders and caecilians may have evolved from within, or close to, one branch of the temnospondyls, especially the small-bodied dissorophoid forms. Others have proposed different relationships, so the exact ancestry of modern amphibians remains an active research question. Either way, temnospondyls show that the early history of land vertebrates was far richer and more varied than a simple ladder of progress from fish to reptiles, mammals and birds.
One of the last known temnospondyls, Koolasuchus cleelandi, lived in what is now Victoria, Australia, about 125 million years ago — long after most of its relatives had disappeared elsewhere. Its survival in cool, polar river systems suggests Australia may have acted as a refuge for these ancient amphibian-grade predators after they had vanished from most of the world.
Scientists name new species of giant amphibian found in retaining wall
Arenaerpeton supinatus was discovered in rocks cut from a nearby quarry that were intended for the building of a garden wall.
A 240-million-year-old fossil of an amphibian that was found in a retaining wall in the 1990s has been formally named and described by scientists at UNSW Sydney and the Australian Museum.
The fossil was originally found by a retired chicken farmer in rocks obtained from a local quarry intended for use in the construction of a garden retaining wall and was subsequently donated to the Australian Museum in Sydney.
An artist's impression of Arenaerpeton supinatus, the ancestor of today's Chinese Giant Salamander.Image: Jose Vitor Silva
Palaeontologist Lachlan Hart, who holds joint roles with UNSW Science and the Australian Museum, says the fossil – named Arenaerpeton supinatus, meaning ‘supine sand creeper’ – shows nearly the entire skeleton, and remarkably, the outlines of its skin.This fossil is a unique example of a group of extinct animals known as temnospondyls, which lived before and during the time of the dinosaurs. We don’t often find skeletons with the head and body still attached, and the soft tissue preservation is an even rarer occurrence.
Lachlan J. Hart, lead author.
Earth and Sustainability Science Research Centre
School of Biological, Earth and Environmental Sciences (BEES)
University of New South Wales
Kensington, New South Wales, Australia.
Arenaerpeton inhabited freshwater rivers in what is now known as the Sydney Basin during the Triassic period, 240 million years ago. Mr Hart says it most likely hunted other ancient fish such as Cleithrolepis, but apart from that, there is not much evidence that tells us about the other animals that Arenaerpeton shared the land and waters with.
Superficially, Arenaerpeton looks a lot like the modern Chinese Giant Salamander, especially in the shape of its head. However, from the size of the ribs and the soft tissue outline preserved on the fossil we can see that it was considerably more heavyset than its living descendants. It also had some pretty gnarly teeth, including a pair of fang-like tusks on the roof of its mouth.
Lachlan J. Hart.
Arenaerpeton looks a lot like the modern Chinese Giant Salamander.Photo: UNSW Sydney/Richard Freeman
Mr Hart says what is exciting about the discovery is that Arenaerpeton is large – estimated to be about 1.2m from head to tail – when most other closely related animals that lived at the same time were small.
The last of the temnospondyls were in Australia 120 million years after Arenaerpeton, and some grew to massive sizes. The fossil record of temnospondyls spans across two mass extinction events, so perhaps this evolution of increased size aided in their longevity.
Lachlan J. Hart.
Dr Matthew McCurry, Senior Lecturer in UNSW’s School of BEES and Curator of Palaeontology at the Australian Museum says the fossil is a significant find in Australian paleo history.This is one of the most important fossils found in New South Wales in the past 30 years, so it is exciting to formally describe it. It represents a key part of Australia’s fossil heritage.
Dr Matthew McCurry, co-author.
Earth and Sustainability Science Research Centre
School of Biological, Earth and Environmental Sciences (BEES)
University of New South Wales
Kensington, New South Wales, Australia.
Publication:
For creationists, of course, Arenaerpeton supinatus presents the usual insoluble problems: it is far too old for their preferred mythology; it lived in a world utterly unlike the one described in their origin stories; and it belongs to a lineage of animals whose history stretches across hundreds of millions of years of evolutionary change, extinction, survival and diversification.
There is no need here for magic, miracles or mysterious acts of special creation. What the fossil shows is exactly what evolutionary biology, geology and palaeontology predict: ancient animals preserved in ancient rocks, belonging to recognisable groups with anatomical features that place them in a wider pattern of descent with modification. Arenaerpeton was not a modern salamander, nor a reptile, nor a fish, but a member of a once-successful group of amphibian-grade tetrapods that flourished long before mammals, birds, flowering plants or humans existed.
And, as so often, the science does not rest on a single isolated specimen interpreted to fit a preconceived dogma. The fossil can be compared with other temnospondyls, dated by its geological context, placed within the ecology of the Triassic Sydney Basin, and understood as part of the broader history of vertebrate evolution. That is how real science works: evidence is discovered, described, compared, tested and incorporated into a larger, coherent explanation.
Creationism, by contrast, has nothing useful to say about why a 240-million-year-old freshwater predator should be preserved in rocks from Australia, why it should resemble other extinct temnospondyls rather than any modern “kind”, or why its anatomy should fit neatly into an evolutionary pattern already established from fossils around the world. All it can do is deny the age, ignore the context, or wave the evidence away as an inconvenience.
So a stone intended for a garden wall has become another small but telling piece of the immense evidential wall against creationism. It is one more fossil from one more ancient ecosystem, showing once again that Earth has a deep history, life has changed profoundly over time, and the Theory of Evolution remains the only explanation that makes sense of what the rocks actually contain.
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