A remarkable spiny arachnid from the Pennsylvanian Mazon Creek Lagerstätte, Illinois
By: Paul A. Selden and Jason A. Dunlop
Summarized by Alivia Tom. Alivia is an undergraduate student at Binghamton University who is working towards a Bachelor’s of Science in the Biology Department. She loves to go on hikes and explore nature in her free time.
What was the hypothesis being tested? In this paper, paleontologists Paul A. Selden and Jason A. Dunlop report the results of studying a newly described that was originally discovered in the 1980s. Researchers examined a spider-like fossil from the late Carboniferous Period (~323–298 mya) to determine whether this specimen represent its own new species based on its identifiable characteristics, or if it belongs to an already existing species.
What data were used? Researchers examine a single specimen from the Pit 15 Northern Mine spoil heap located in the Pennsylvanian Mazon Creek in Illinois, USA. This area is classified as a Lagerstätte, which is a geologic unit that has the ability to preserve fossils extremely well. Many other well-preserved fossils have been discovered from this area, including other arachnids and mites. This specimen was compared to many other identified fossil organisms, mainly other arachnids. The data for the other species was sourced from data sets in research papers created by many other scientists. Some of the body parts that were compared included its abdomen and legs, as well as the shape of its body.
Methodology: The person who had found the fossil in the 1980s, Bob Masek, decided to leave the fossil in water during the winter. This allowed the water to run through the existing cracks of the material surrounding the fossil, and then expand through freezing. A hammer was then used on the surrounding material to reveal the fossil. After the discovery and reveal of this fossil, it was passed to the Douglass family Prehistoric Life Museum in Illinois, USA, and then donated to The Field Museum of Natural History for further research. A Canon EOS 5DSR digital camera alongside a Leica MZ16 microscope and low-angled light were used to take pictures of this fossil. When these two instruments were used together, the intricate forms and structures of the fossil were revealed. Pictures of different angles of the fossil were taken to capture details that other angles could not see, and these pictures were layered on top of each other. Through the combination of multiple photographs and further detailing using a microscope, drawings of the fossil were created using Affinity Designer 2 (Fig 1.). Researchers contrasted the differences from the body layout of the new specimen to other studied species, such as how each body part was attached to each other, how they fused to each other, and how the lengths of each body part compared.
Results: This fossil was classified as an arachnid, because of its four pairs of legs, two body parts, fused head and chest, and segmented rear end. However, it was not placed into any existing species due to its distinct large spines on its legs, a very fused head and chest, and very large and equivalent legs. Scientists classified this specimen as a new genus and species, after comparing many of its characteristics to other existing or extinct species that appeared to be similar. This conclusion was reached after determining that the characteristics of the fossil did not match any known arachnid species. Some of its differences include its large spiky spines. They named the new genus and species Douglassarachne acanthopoda. Its differences also do not allow it to be placed into any existing order. An example of a difference that it had was that all its legs appeared to have the same frame and length, setting it apart from harvestmen. Harvestmen are an order of arachnids that have an oval shaped body and thin legs that are of varying lengths.
Why is this study important? This study could make scientists consider a wider range of possible body plans that may have existed in the late Carboniferous, as this arachnid’s body plans did not match any that were previously discovered. Scientists also created hypotheses of what the purpose of these spiny spikes were used for. They hypothesized that they could have been used for defense, creating a longer handling time for predators, increasing their ability to escape and survive.
Broader implications beyond this study: Further studies on this area could also reveal more about the fossil record of the Carboniferous period, as Mazon Creek is known to be able to preserve soft tissue. Even fossils with hard tissues are difficult to preserve, and fossils with soft tissue are even more difficult to preserve as their bodies typically decay quickly after death..
Citation: Selden, P. A., & Dunlop, J. A. (2024). A remarkable spiny arachnid from the Pennsylvanian Mazon Creek Lagerstätte, Illinois. Journal of Paleontology, 1–7. doi:10.1017/jpa.2024.13