Placenticeras pseudoplacenta from the Mancos Shale of New Mexico

One last Ammonite from the Mancos Shale (Turonian stage of the Cretaceous) of Sandoval County, New Mexico: Placenticeras pseudoplacenta. This specimen is a little rough as it has fragments from several whorls attached. the left side is the most intact visibly and I may eventually try to remove the rest of the whorl pieces to make it look cleaner. By my estimations the full sized, intact specimen would have been 6-8" in diameter but only 3" of the current specimen is whole. P. pseudoplacenta is a narrow, flat, disc like shell with little ornamentation on the exterior of the shell. The suture pattern is very complex with a large number of nodes and lobes each with many smaller knobs.

Right side

Left side

Keel and cross section of a chamber

A closer view of the sutures

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.

Prionocyclus hyatti (robust form) from the Mancos Shale of New Mexico

These large, bumpy ammonites are the robust form of Prionocyclus hyatti from the Mancos Shale (Turonian stage of the Cretaceous) of Sandoval County, New Mexico. None of the sutures are visible but the form of the shell is what helps to ID it. The robust form of the shell is wider than the normal form and has distinct, knobby ribs. There is also a noticeable raised keel. The cross section of the chambers is roughly square.

Specimen #1 still has part of the nodule, that once surrounded it, still attached. Ammonites in the Mancos shale are often found in nodules. Sometimes they are septarianized as well.

Right side

Left side

Keel

Closer view of the right side

Specimen #2 is larger than the previous specimen and does show some septarian features.
Right side

Left side

View of the cross section of the last chamber

Keel

Part of the fossil shows septarian features like the "seam" seen below.

The fossil had broken while in transit which allows a view of the calcite filling the interior.

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.

Spathites puercoensis ammonite from the Mancos shale of New Mexico

Here are another couple of Ammonites from the Carlile shale member of the Mancos Shale (Turonian stage of the Cretaceous) of Sandoval County, New Mexico. They are specimens of Spathites puercoensis. This ammonite is small but somewhat robust with some obvious ribs near the keel.  Each whorl overlaps the previous by about 95%. As these are steinkerns and no original shell is left, the suture pattern is easily visible and consists of a number of alternating "U" shapes, of differing depth, accented with some smaller zigzags.

Specimen #1
Right side

Left Side

Keel

A cross section view of the last suture chamber

Specimen #2
Left side

Right side (note the rock plug in the center which indicates there were likely more whorls that eroded away before the fossil was found)

Keel

Cross section view of the last suture.

A closer view of the suture pattern.

The publication "Contributions to Late Cretaceous Paleontology and Stratigraphy of New Mexico Part II". Bulletin 114. New Mexico Bureau of Mines and Mineral Resources. contains a paper by W. A. Cobban titled "The Late Cretaceous ammonite Spathites Kummel and Decker in New Mexico and Trans-Pecos Texas" from which this illustration of the suture patterns of S. puercoensis comes.

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.

Coilopoceras springeri ammonite from the Mancos Shale of New Mexico

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%.

Right side

Left side

Keel

 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.