This is Mazon Monday post #21. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Euproops was a horseshoe crab. There are two species of horseshoe crab found in the Mazon Creek biota, Euproops danae (common) and Paleolimulus sp. (extremely rare). Both are known from other Carboniferous fossil localities around the world. As you can see in the pictures, they both look very similar to modern species. The holotype (shown below) resides at the Illinois State Museum. This picture appears here on georgesbasement.com.
There are a few great examples on that page.
The Field Museum had this specimen on display during Member Nights in 2019.
Dave's Down To Earth Rock Shop has a very large specimen.
Here is the text from Creature Corner. The column first appeared in February 1987.
EUPROOPS (horseshoe crab)
Time and again this column has had as it's subject an animal that could easily have been the primitive ancestor of a Sunday Supplement "Living Fossil" article. Soit is again with the "horseshoe crab", Euproops. Our horseshoe crab, Genus Euproops, is a member of the Phylum Arthropoda,Subphylum Chelicerata, Class Merostomata, Subclass Xiphosura and Superfamily Euproopacea.
Our creature for this month can trace its ancestry back to the Cambrian Period. The xiphosura of that timehaving all the appearance of a trilobite; tri-lobed, 12 movabile segments and a sword-like telson (tail). Modern horseshoe crabs have a fused median or central shield that is smooth, with insignificant lobes. Paleozoic xiphosurans were in a state of transition.Terms used to describe trilobites do not "fit' our Euproops. For brevity Euproops has a head-shield, median and a tail. The head-shield, that bore spines in some species, was almost half the body length, and is quite oftenthe only portion found in concretions. The median is almost circular in shape, bearing furrows that denote the positions of the fused segments. Spines, common to all horseshoe Crabs, carry on over the flattened edge or rim of the median and up and over the median furrows. This last feature is used in identifying Euproops. Appendages are located beneath the animal, and are never (?) seen in concretions. Last is the telson, very often lacking on our Mazon Creek fossils.
The species Euproops danae is classified as "common", being the horseshoe crab most often found in Mazon Creek concretions. It is found mainly in Braidwood (non marine) locations, although a few specimens are found in Essex (marine) localities. The fact that it was a denizen of fresh water has been accepted for more than a century. Euproops is quite often found in concretions that contain Arachnids, fresh-water clams, millipedes and plant fragments. Surprising because modern limulids are exclusively marine. There are several species of Euproopids. All became extinct during the Paleozoic.
