Trapdoor spider terrorised Australia’s forests 15 million years ago

For the first time, fossilised remains of a brush-footed trapdoor spider have been found. The hairy monstrosity which lived 11–16 million years ago in Australia is five times larger than its modern relatives.

Megamonodontium mccluskyi is described in a paper published in the Zoological Journal of the Linnean Society.

Fossil spider mirror with scale
Megamonodontium mccluskyi. Supplied.

The spider is related to the modern Monodontium – a genus of brush-footed trapdoor spider, part of the Barychelidae group of spiders. Today, these creepy-crawlies are very small and can be found in the rainforests of Singapore, Indonesia and Papua New Guinea.

The ancient Megamonodontium was five times larger – the fossil’s abdomen and thorax are appear to be about 10mm long, and the legs perhaps a further 20–25mm. The entire spider might have been 50mm from toe to toe.

This makes the ancient brush-footed trapdoor specimen roughly the size of a wolf spider.

Today, the largest spiders are South America’s goliath birdeaters which have bodies measuring 13 cm.

During Earth’s Late Carboniferous period (also known as the Pennsylvanian, 323.2 million to 298.9 million years ago) giant spiders called Megarachne existed, with bodies more than half a metre in length.

While not the largest spider ever, Megamonodontium is huge compared to its modern-day relatives.

It is one of only four spider fossils found on the entire Australian continent. It was discovered McGraths Flat near the regional New South Wales town of Gulgong.

Megamonodontium lived during the middle of the Miocene epoch (23–5 million years ago). Globally, temperatures were much higher than today and Australia was much wetter, with most of the northern parts of the continent covered in rainforest.

Drawing of large spider in forest with large flightless birds in background
Megamonodontium mccluskyi recreation. Supplied.

“The closest relative of this fossil now lives in wet forests in Singapore through to Papua New Guinea,” Dr Simon McClusky, an associate professor of geophysics at the Australian National University in Canberra. “This suggests that the group once occupied similar environments in mainland Australia but have subsequently gone extinct as Australia became more arid.”

Though not an author on the research paper, McClusky discovered the fossil in June 2020 and, thus, gives his name to the newly named species.

“Scanning electron microscopy allowed us to study minute details of the claws and setae on the spider’s pedipalps, legs and the main body,” says co-author Michael Frese, an associate professor at the University of Canberra. “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.”

“Not only is it the largest fossilised spider to be found in Australia but it is the first fossil of the family Barychelidae that has been found worldwide,” says Queensland Museum arachnologist and supervising author Dr Robert Raven. “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 fossilised.”

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