|Gonioceras occidentale from Illinois, plate LVII of Clarke (1897). This specimen shows part of the wedge-like flaring of the shell and the curved septa.|
Of course, in the field, you're liable to just find a chunk with those distinctive wavy septa:
|Gonioceras in the wild, skooshed flat and otherwise worse for wear, from the lower to middle Mifflin Member of the Platteville Formation.|
Although Gonioceras certainly cannot be accused of simply doing what the other nautiloids were doing, its innovative structure does not appear to have caught on. In Minnesota, Gonioceras is primarily a Platteville Formation concern (Stauffer and Thiel 1941; Catalini 1987). It is generally thought of as a bottom-feeder, sometimes interpreted as a crawler but perhaps analogous to a flounder (Vickers Rich et al. 1996). Like other nautiloids, its propulsion would have moved it primarily backward, so the pointed end was the leading end of the animal when it had to get going.
Catalani, J. A. 1987. Biostratigraphy of the Middle and Late Ordovician cephalopods of the Upper Mississippi Valley area. Pages 187–189 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.
Clarke, J. M. 1897. The Lower Silurian Cephalopoda of Minnesota. Pages 760–812 in Ulrich, E., W. Scofield, J. Clarke, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(2). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.
Stauffer, C. R., and G. A. Thiel. 1941. The Paleozoic and related rocks of southeastern Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Bulletin 29.
Vickers Rich, P., T. H. Rich, M. A. Fenton, and C. L. Fenton. 1996. The fossil book: a record of prehistoric life (corrected republication of 2nd edition). Dover Publications, Inc., Mineola, New York.