A 308 million-year-old arachnid stands out for its spiny legs

May 17. () –

A strange, unclassified fossilized arachnid, discovered in 308-million-year-old rocks from an Illinois site, is described in an article in the Journal of Paleontology.

All kinds of arachnids crawled through the Carboniferous forests of North America and Europe. These included familiar animals we would recognize, such as spiders, harvestmen and scorpions, as well as exotic animals now found in warmer regions, such as whip spiders and whip scorpions.

But in these habitats there were also quite strange arachnids that belonged to now extinct groups. Even among these rarest species now lost to time, the one that stars in the new study could have stood out for its armored legs.

This ancient creature has been described by Paul Selden of the University of Kansas and the Natural History Museum in London and Jason Dunlop of the Berlin Nature Museum.

“Douglassarachne acanthopoda comes from the famous Mazon Creek locality in Illinois and is about 308 million years old,” he said. it’s a statement lead author Selden. “This compact arachnid had a body length of approximately 1.5 centimeters and is characterized by its remarkably robust and spiny legs, “so it is very different from any other known arachnid, living or extinct.”

The researcher said the geological formation of the find is an important source of information for fossil arachnids, and represents the first time in Earth’s history that most living groups of arachnids were found together. However, the fauna was still quite different from today.

“Spiders were a fairly rare group, known at the time only from primitive lineages, and shared these ecosystems with several arachnids that became extinct long ago,” said co-author Dunlop. “Douglassarachne acanthopoda is a particularly impressive example of one of these extinct forms. The fossil’s very spiny legs are reminiscent of some modern harvesters, but its body structure is quite different from that of a harvester or any other known group of arachnids.”

UNLIKE THE ORDERS OF KNOWN ARACHNIDS

This led the two scientists to conclude that it does not belong to any of the known arachnid orders.

“Unfortunately, you can’t see details like the mouth parts, making it difficult to say exactly which group of arachnids are their closest relatives,” Selden said. “It could belong to a larger group, which includes spiders, whip spiders and whip scorpions. Whatever their evolutionary affinities, these spiny arachnids appear to come from a time when arachnids were experimenting with a variety of different body plans.

According to the team, the Mazon Creek site is one of the most important windows into life in the late Carboniferous, producing a wide range of fascinating plants and animals. The current fossil was discovered in a clay and ironstone concretion in the 1980s by Bob Masek and later acquired by the David and Sandra Douglass Collection and displayed in their Museum of Prehistoric Life.

“The genus name Douglassarachne recognizes the Douglass family, who kindly donated the specimen to the Field Museum of Natural History in Chicago for scientific study once it became apparent that it represented an undescribed species,” Dunlop said. “So, acanthopoda refers to the animal’s unique and characteristic spiny legs.”