This is Mazon Monday post #78. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Today, we are having a look at Amynilyspes wortheni, an extinct species of pill millipede. A. wortheni was described by Samuel Hubbard Scudder in 1882, a giant in the field of fossil insects and other arthropods during the 1800's. The description of the species appeared in the paper S. H. Scudder. 1882. Archipolypoda, a subordinal type of spined myriapods from the Carboniferous formation. Memoirs of the Boston Society of Natural History 3:143-182. The animal is named for Amos Henry Worthen, who was a paleontologist and geologist from Illinois. He was the second state geologist and the first curator of the Illinois State Museum. Fossil Friday #73 featured a very nice specimen from ESCONI member Connor Puritz.
Pill millipedes look very much like pill bugs, which are very different. Pill bugs are isopods and belong to the Subphylum Custacea any similarity between the two is a case of convergent evolution.
A. wortheni appears on page 48 in "The Mazon Creek Fossil" Fauna by Jack Wittry.
This spinous 25 mm-long, air-breathing arthropod known as the Pill Millipede is so named for its remarkable ability to curl into a tight ball when threatened by a predator. It accomplished this by stretching apart its 13 or 14 overlapping back plates (tergites) and enclosing the 40 or so legs and soft body parts in a small central space. The name millipede-thousand feet-is obviously an overstatement.
Amynilyspes wortheni is the second most common millipede in the Mazon Creek Fauna. Specimens generally show 14 body segments, large spines along the edge of the back, and a row of short spines down the middle. Despite its common name, rolled examples are rare. This animal was originally described by Samuel Scudder over a century ago. In addition to the Mazon Creek Lagerstätte, only a few other sites in North America have yielded fossil pill millipedes.
There is a short description of A. worheni in chapter 13 "Myriapods and Arthropleurids" of the "Richardson's Guide to the Fossil Fauna of Mazon Creek". That chapter was written by Joseph T. Hannibal of the Cleveland Museum of Natural History.
Amynilyspes wortheni Scudder Figures 13.1, 13.2
Amynilyspes wortheni is a medium-sized, spiny pill millipede with 14 tergites (one more than any modern pill millipede) and large eyes. This animal was armored by large spines along the edge of its back and by a row of small spines down the middle of its back.
Most modern oniscomorphs are associated with the forest floor. Based on the presence of stout spines on this species, however, it may have lived in more open habitats, possibly including arboreal habitats (Hannibal and Feldmann, 1981, p. 744). Amynilyspes is the most common oniscomorph found in the Mazon Creek fauna. The type specimen of A. wortheni was presumably found along Mazon Creek; specimens have since been found in Pit 11 and Pits 1 and 6-thus, in both the Essex and Braidwood faunas.
Specimens
From Fossil Friday #73.
From "The Mazon Creek Fossil Fauna".
