The extraordinary fossil remains of Australia's biggest spider, which lived 16 million years ago, have been discovered.
In 2017, paleontologists from the Australian Museum (AM) and the University of New South Wales (UNSW) unearthed the ancient remains at the McGraths Flat in central New South Wales — a famous fossil site consisting of iron-rich rock called "goethite."
The newly found fossil has been scientifically named Megamonodontium mccluskyi. Fossil is estimated to be between 11 and 16 million years old.
As per the official release, this find is particularly noteworthy because just a few spider fossils have been unearthed in Australia.
“Only four spider fossils have ever been found throughout the continent, making it difficult for scientists to understand their evolutionary history. That is why this discovery is so significant; it reveals new information about the extinction of spiders and fills a gap in our understanding of the past,” said Matthew McCurry in the press release.
Using an advanced stacking microphotography method, the researchers thoroughly inspected and scanned the well-preserved fossil of this ancient spider.
This approach revealed previously hidden anatomical features of fossils.
“Scanning electron microscopy allowed us to study minute details of the claws and setae on the spider’s pedipalps, legs, and the main body. Setae are hair-like structures that can have a range of functions. They can sense chemicals and vibrations, defend the spider against attackers, and even make sounds,” said Michael Frese, an associate professor at the University of Canberra.
Australian Museum (AM) and University of New South Wales
The fossil findings suggest a strong resemblance to the modern genus Monodontium, known as a brush-footed trapdoor spider. However, this prehistoric creature was notably larger, approximately five times the size, compared to this living species.
“The closest living relative of this fossil now lives in wet forests in Singapore through to Papua New Guinea. This suggests that the group once occupied similar environments in mainland Australia but have subsequently gone extinct as Australia became more arid,” added McCurry.
Moreover, this comprehensive analysis established that this spider represents the first discovery of a fossil from the Barychelidae family.
Barychelidae is a mygalomorph spider family, which notably includes brush-footed trapdoor spiders. This spider family is noted for their peculiar burrowing activity and may be found all over the world, including Australia, Asia, Africa, and the Americas.
“Not only is it the largest fossilized spider to be found in Australia, but it is the first fossil of the family Barychelidae that has been found worldwide. There are around 300 species of brush-footed trapdoor spiders alive today, but they don’t seem to become fossils very often. This could be because they spend so much time inside burrows and so aren’t in the right environment to be fossilized,” said Robert Raven, arachnologist.
The fossil is now housed in the museum’s paleontology collection and is accessible online for researchers to conduct further studies.
The findings were reported in the Zoological Journal of Linnean Society.
The aridification of the Australian continent led to the diversification of mygalomorph spiders in the Miocene, but a depauperate fossil record has made it difficult to investigate evolution across this epoch. Here, we describe the first fossil barychelid spider (Araneae: Barychelidae) in the world and the second fossil mygalomorph spider from Australia. It is placed as a new genus and species (Megamonodontium mccluskyi gen. et sp. nov.). Megamonodontiumresembles Monodontium Kulczyński, 1908, a genus that persists in rainforests through Singapore, Indonesia and Papua New Guinea. The new specimen is the second largest spider fossil in the world and is approximately five times larger than extant Monodontium. The fossil shows that this lineage once occupied mesic rainforest habitats in Australia but has since been replaced by other spiders.