The Late Carboniferous appears to have been a time of remarkable Arachnid diversity, with known fossils including long-established Arachnid groups such as the Scorpions and Harvestmen, as well as the first appearance of other groups such as the Spiders, Whip Spiders, Whip Scorpions, Tick Spiders, and Camel Spiders. In addition to these living groups, Carboniferous deposits have yielded fossils of a number of entirely extinct groups such as the Trigonotarbids, Phalangiotarbids, and Haptopods. A number of Carboniferous fossil 'Spiders' are also likely to represent extinct, non-Spider groups, as they do not possess spinneretes (silk-producing organs) which are considered to be the diagnostic organ for Spiders by modern Arachnologists.
In a paper published in the Journal of Paleontology on 17 May 2024, Paul Selden of the Department of Geology at the University of Kansas, and the Natural History Museum in London, and Jason Dunlop of the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Science, describe a new species of Arachnid from the Late Carboniferous Mazon Creek Fauna of Illinois.
The Mazon Creek Fossil-Lagerstätte produces a wide range of terrestrial and shallow-marine fossils preserved in ironstone concretions collected from the spoilheaps of coal strip mines around Braidwood in northeastern Illinois. These deposits have provided a valuable insight into the flora and fauna of the Late Carboniferous, including a wide range of Arachnids, with every known order found here, with the exception of the Haptopoda, which is known only from the Late Carboniferous of the UK.
The new species is described from a single specimen which came from a concretion found in the 1980s by fossil hunter Bob Masek on the spoil heap of Pit 15 Northern Mine near Essex in Kankakee County, Illinois. Masek split the concretion by leaving it outside in water during the winter, which enables frost to enter natural cracks in the hard ironstone and widen them, then striking it with a hammer to get it to split along a single plain. The specimen was acquired from Masek by David Douglass of the Prehistoric Life Museum, where it was displayed until 2023, when the importance of the fossil was realised, and it was donated to the Field Museum of Natural History in Chicago.
The new species is named Douglassarachne acanthopoda, where 'Douglassarachne' means 'Douglass's Arachnid' in honour of David Douglass for donating the fossil, and 'acanthopoda' means 'prickly legs' in reference to the numerous spines on the legs of the specimen.
Douglassarachne acanthopoda has a bodylength of about 15 mm, and a body roughly divided into two parts, interpreted as an anterior prosoma and a posterior segmented opisthosoma. The prosoma is covered by a subtriangular dorsal shield, which is divided, and has a slight anterior projection. The chelicerae and pedipalps cannot be seen. The legs are robust, and of roughly even length, with a notable covering of spines. The connection between the prosoma and the opisthosoma is broad, represented by only a slight narrowing of the body. The opisthosoma has at least eight visible tergites, and lacks any form of s spines or large tubercles, with the exception of what appears to be a terminal anal tubercle.
Douglassarachne acanthopoda, reconstruction of the possible appearance of the animal in life. Seldon & Dunlop (2024).Douglassarachne acanthopoda does not clearly belong to any described order of Arachnids, living or extinct. The spiney legs of the species are similar to those seen in Armoured Harvestmen, Podoctidae, but there is no other indication of a close relationship, and spines have arisen numerous in numerous Arthropod groups as an anti-predation measure.
Seldon and Dunlop note that there is a precedent for naming Carboniferous Arachnid orders from a single specimen, the Haptopoda having been described in this way, but decide against doing this, on the basis that the discovery of another specimen of Douglassarachne acanthopoda with preserved chelicerae and pedipalps might reveal a closer relationship to another Arachnid group than is currently obvious, and the need for a revision of the numerous Carboniferous 'Spiders' now thought not to belong to that group. For the time being they settle for assigning the new species tentatively to the clade Pantetrapulmonata, which united the extant Spiders, Whip Spiders, and Whip Scorpions, with the extinct Trigonotarbids.
See also...
%20(1).png)
