A new species of prehistoric arachnid has been named and described from the famous Mazon Creek fossil site in Illinois, USA.  The new species has been named Douglassarachne acanthopoda.  The fossils are believed to be around 308 million years old.  D. acanthopoda is characterised by its remarkably robust and spiny legs.  Its appearance is strikingly different from all other living or extinct arachnids.  The preserved character combination examined by the researchers does not permit easy referral to any known arachnid, living or extinct.  Thus, the new fossil in placed as Arachnida, in the clade Tetrapulmonata.  The Tetrapulmonata consists of the whip scorpions and the true spiders.

Douglassarachne acanthopoda fossil. A bizarre, Late Carboniferous arachnid. Picture credit: Professor Paul Selden.

Picture credit: Professor Paul Selden

A Bizarre Arachnid with Spiny Legs – Douglassarachne acanthopoda

This new Carboniferous invertebrate has been described in a scientific paper published in the “Journal of Paleontology”.  Researchers Jason Dunlop from the Museum of Natural History, Berlin and Paul Selden (University of Kansas/London Natural History Museum), wrote the paper.

During the Carboniferous, many different types of arachnids evolved.  These included forms that we are familiar with today, such as the true spiders, harvestmen and scorpions. There were also many exotic animals that today are confined mainly to the tropics. Animals like the whip spiders and whip scorpions.  The fossil record suggests that in the coal forests, true spiders were quite rare.  Among these were primitive forms and other lineages that have no living descendants.

To read a recent article about the discovery of the oldest harvestmen from Germany: The Oldest Harvestmen from Germany are Scientifically Described

Preserved Inside a Clay-Ironstone Nodule

The Mazon Creek site is famous for its remarkable fossils.  It preserves the flora and fauna of a Late Carboniferous tropical forest.  The ecosystem was very different to modern ecosystems.  The Douglassarachne acanthopoda specimen (number FMNH PE 91366), was discovered in the 1980s by Bob Masek in a clay-ironstone concretion. Bob deployed a common method for splitting the concretion.  He placed the nodule outside immersed water throughout the winter.  The cold and frost penetrated natural fissures in the concretion along the plane containing the fossil.  After the weather had done its work, a blow from a geology hammer was enough to split the nodule and reveal the fossil.

The specimen was acquired by David Douglass and was displayed at the Douglass family’s Prehistoric Life Museum.  The fossil was donated to the Field Museum of Natural History in Chicago in 2023 so it could be studied.

The body of the D. acanthopoda measures 15.4 mm in length.  The extremely spiny legs probably evolved to deter predators. Whilst it might superficially resemble an extant harvestman or mite, it differs significantly from any extant harvestman or any other known arachnid group.  Unfortunately, the mouthparts (chelicerae) are not preserved.  This makes classification difficult.  Douglassarachne has bene tentatively assigned to the Tetrapulmonata clade.  This clade includes the true spiders, whip spiders and whip scorpions.

Diverse Arachnids

Whilst is it not possible to determine the exact evolutionary relationship of Douglassarachne acanthopoda, it is noted that during the Carboniferous a diverse variety of arachnids evolved.  Some of these families later died out.  Many forms became extinct during the so-called “Carboniferous Rainforest Collapse” when global climate change led to the decline of the coal forests.

Everything Dinosaur acknowledges the assistance of a media release from the Museum für Naturkunde Berlin in the compilation of this article.

The scientific paper: “A remarkable spiny arachnid from the Pennsylvanian Mazon Creek Lagerstätte, Illinois” by Selden, P. A. and Dunlop, J.A. published in the Journal of Paleontology.

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