This is a very odd fossil that I collected from a Pennsylvanian aged black shale site in North Central Illinois.
i have been collecting this site for many years and have never found anything like it.
The specimen measures approximately 3”.
The site primarily consists of a Thylacocephalan type arthropod along with a variety of fish and a few nautiloids.
it is very similar to the Mecca Quarry Shale of Indiana.
My best guess is that it is some type of nautiloid or possibly a spiral coprolite.
Any suggestions would be appreciated.