More than 300 million years ago, various arachnids inhabited the Carboniferous coal forests of North America and Europe. These included familiar species such as spiders, harvestmen, scorpions, as well as more exotic creatures like whip spiders and whip scorpions. Among these ancient arachnids were also bizarre and now-extinct species, one of which recently caught the attention of researchers for its distinctive up-armored legs. The ancient arachnid, named Douglassarachne acanthopoda, was described in a new paper published in the Journal of Paleontology by Paul Selden from the University of Kansas and Jason Dunlop from the Museum für Naturkunde Berlin.
Douglassarachne acanthopoda was found in the famous Mazon Creek locality in Illinois and is approximately 308 million years old. With a body length of about 1.5 centimeters, this compact arachnid is characterized by its robust and spiny legs, making it quite unlike any other arachnid species known to have existed, whether living or extinct. The Carboniferous Coal Measures are an important source of information for fossil arachnids, as they represent a time in Earth’s history when most living arachnid groups coexisted. However, the fauna of that time was significantly different from what we see today, with spiders being a rare group and various other arachnids that have since become extinct sharing ecosystems with them.
Co-author Dunlop noted that Douglassarachne acanthopoda is an impressive example of an extinct arachnid species. Despite having legs reminiscent of modern harvestmen, its body plan sets it apart from known arachnid groups. This led the researchers to conclude that it does not belong to any of the known arachnid orders. Due to the lack of visible mouth parts, determining its closest relatives is challenging. It is possible that this spiny arachnid belonged to a broader group that includes spiders, whip spiders, and whip scorpions. These ancient arachnids with unique body plans may have come from a time when arachnids were experimenting with different forms before facing extinction events, such as the Carboniferous Rainforest Collapse or the end-Permian mass extinction.
The Mazon Creek fossil locality is considered a crucial window into life during the late Carboniferous period, offering a glimpse into a wide range of fascinating plants and animals from that time. The fossil of Douglassarachne acanthopoda was discovered in a clay-ironstone concretion in the 1980s by Bob Masek and later acquired by the David and Sandra Douglass Collection for display in their Prehistoric Life Museum. The genus name Douglassarachne honors the Douglass family for donating the specimen for scientific study, while the species name acanthopoda refers to the arachnid’s unique spiny legs. This study highlights the importance of fossils like Douglassarachne acanthopoda in understanding the diversity and evolution of ancient arachnids during a pivotal period in Earth’s history.