Down Underneath Got here A Spider – The Bristol Dinosaur Venture

Visitor Writer – Dr Rachel Kruft Welton
Palaeobiology MSc Graduate

It’s attainable, if in case you have by no means lived in Australia, that you’ve by no means come throughout a brush-footed trapdoor spider. These beauties are considerable in Australia and may be discovered from the tropical rainforests to intertidal coastal areas to the dry inside. They reside in shallow burrows, typically with a double entrance door, and a few are identified to climb timber the place they make burrows in appropriate cracks and cervices.

They’re mygalomorph spiders, which suggests they’re energetic hunters with vertical biting chelicerae. The comb-footed (aka brushed) trapdoor spiders, Barychelidae, are a sister group to the higher identified and extra feisty tarantulas, and bigger species may be simply mistaken for them.

A Segocrypta trapdoor spider
An extant member of the Barychelidae – Brush-Footed Trapdoor Spider – household from Queensland, Seqocrypta jakara. Credit score Robert Whyte.

Brush-footed trapdoor spiders have a number of distinguishing options, not all of which I’ll bore you with right here. They are often distinguished from different mygalomorph spiders by their physique proportions, i.e., relative leg lengths, tibia to tarsal lengths, paired tarsal claws, and distribution of hairs (setae), amongst different traits.

Brush-footed trapdoor spiders have collections of bristles on their ft which permit them to climb up surfaces so easy that Spider-man himself would wish a ladder. Every hair interacts on the molecular stage with the surroundings round it, creating tiny electrical points of interest known as van der Waals forces. These act to connect the spider to a floor.

The energy of the forces is additive and will increase with the variety of bristles of the tufts. Energy is additional enhanced by tiny micro-hairs on every bristle. The cumulative impact can permit some spiders to hold the other way up with prey as heavy as themselves clamped of their jaws.

The fanned claw tufts of a barychelid spider. Fine hairs fan around two thin dark hook structures.
Claw tufts of a barychelid spider. Credit score: Robert Raven / Queensland Museum

The Australian fossil file is, sadly, very patchy, and by patchy I imply just about invisible.  Solely 4 fossil spiders have been described from the continent thus far, and solely two of those are mygalomorph spiders. The evolutionary historical past of those spiders remains to be very obscure, so the latest description of a brush-footed trapdoor spider (McCurry et al. 2023) relationship from the Miocene could be very thrilling.

The fossil is 11 to 16 million years previous, and dates to a time when the west coast of Australia was drying out, altering from rainforest to a extra arid surroundings. The fossil is exceptionally effectively preserved, and comes from McGrath’s Flats, a lagerstätte in New South Wales, 200km NE of Sydney.

A fossilised spider in red rock
Megamonodontium mccluskyi. (Michael Frese)

McCurry et al. used a scanning electron microscope to intimately examine the fossil, which was so exquisitely preserved that particular person setae might be recognized. The physique proportions allowed the spider to be positioned confidently throughout the Barychelidae, and so they named the brand new species Megamonodontium mccluskyi.

Nevertheless, there was an issue. This historical brush-footed trapdoor spider doesn’t have furry ft, whereas each extant species of Australian Barychelid spider do have tufty toes. This fossil should belong to a extra basal lineage.

A little bit little bit of looking out later, led the researchers to a bunch of tiny, litter-dwelling brush-footed trapdoor spiders known as Monodontium, which additionally lack tufty toes. This genus will not be present in Australia, and as an alternative inhabits the tropical rainforests of Singapore, Indonesian and Papua New Guinea. Megamonodontium mccluskyi most intently resembles this genus.

The Miocene surroundings within the McGrath Flats space of Australia was much like that of modern-day Southeastern Asia rainforests, however the surroundings was altering. There’s a well-documented turnover of vertebrate fauna (Murray & Megirian, 1992) from this time, however which different varieties of fauna had been affected will not be identified. This fossil offers a number of the first proof that invertebrates had been challenged as tree species and cover cowl altered. It seems that this spider belonged to a lineage that went extinct because the local weather modified.

In regards to the Writer

Dr Rachel Kruft Welton accomplished the Palaeobiology MSc course on the College of Bristol in 2023. Rachel’s masters targeted on the drivers of evolution and extinction of bivalves, notably throughout the Cretaceous – Palaeogene boundary.

Article edited by Rhys Charles


McCurry, R., Frese, M., & Raven, R. (2023) A big brush-footed trapdoor spider (Mygalomorphae: Barychelidae) from the Miocene of Australia. Zoological Journal of the Linnean Society. zlad100

Murray, P. & Megirian, D. (1992) Continuity and distinction in center and late Miocene vertebrate communities from the Northern Territory. The Beagle: Information of the Museums and Artwork Galleries of the Northern Territory. 9, 195 – 217

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