This is the "Fossil Friday" post #41. Expect this to be a somewhat regular feature of the website. We will post any fossil pictures you send in to [email protected]. Please include a short description or story. Check the #FossilFriday Twitter hash tag for contributions from around the world!
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Today's fossil is a "hooded tick spider" from the Pennsylvanian Period of Illinois. It belongs to a group of animals called ricinuleids, which is an extant group of spiders. The specimen was found by ESCONI member Ben Riegler in Vermilion County, IL. The fossil was discovered in a concretion embedded in an outcropping of the Energy Shale, which is located between the underlying Herrin No. 6 Coal and the overlying Anna Shale. The stratigraphic unit dates to between 306 to 308 million years ago. Ben noticed this fossil was significant and donated it to the Illinois State Museum in 2015. Recently (December 2020), it was described as a new species, Curulioides bohemondi in a paper in the Journal of Paleontology. Congratulations, Ben, awesome find!
A new, giant ricinuleid (Arachnida, Ricinulei), from the Pennsylvanian of Illinois, and the identification of a new, ontogenetically stable, diagnostic character
Abstract
A new fossil ricinuleid, Curculioides bohemondi n. sp., from the Pennsylvanian Energy Shale of Illinois is described from a single specimen. It is the largest ricinuleid species yet described, living or extinct. The Energy Shale represents a new geographic locale for fossil ricinuleids, a sparsely distributed group. The species is distinguished from other members within the genus by the possession of very large (0.09 mm) carapace tubercles at a very low (30 mm-2) density. Statistical analyses are performed on extant and fossil ricinuleids to determine how their tubercles change throughout ontogeny, culminating in the recovery of a new ontogenetically stable diagnostic character: the tubercle coefficient (a measure of the size of the tubercles relative to body size).
