Today I have an Ammonite from New Mexico to show you. It's a Coilopoceras springeri from the Carlile Shale member of the Mancos Shale (Turonian stage of the Cretaceous), Sandoval County, NM. The fossil is very thin in cross section, it reminds me of a frisbee, and has a very complex suture pattern. Each whorl overlaps the previous whorl by about 95%.
A closer detail of the keel from the side. I'm not sure if the segmentation that is shown is part of the shell or just an erosional feature.
Keel with a cross section view of the last suture chamber.
A closer view of the suture pattern.
I found a publication, "The Upper Cretaceous (Turonian) ammonite family Coilopoceratidae Hyatt in the Western Interior of the United States." W. A. Cobban and S. C. Hook. 1980. United States Geological Survey Professional Paper 1192:1-28, that has a good description of this species and this helpful drawing (figure 11, page 18) of a few typical suture patterns from C. springeri specimens.
Thanks to Mike (PFooley on the Fossil Forum) for this fossil that he offered up as part of an auction to help defray some of the operating costs of the Fossil Forum website.