The preserved shells and internal casts of ammonites are common occurrences in Mesozoic marine sediments around the world and are often used by paleontologists as stratigraphic markers. However, they are only rarely preserved in the Smoky Hill Chalk Member of the Niobrara Chalk, and I have thus pretty much avoided saying much about them. Recently, however, I've had opportunities to collect fossils in other Cretaceous formations in north-central Kansas and have been able to collect several species of ammonites. In addition, I co-authored a paper with Anthony Maltese about the first discovery of a heteromorph ammonite in the Smoky Hill Chalk (see photos below):
Everhart, M.J. and
Maltese, A. 2010. First report of a heteromorph ammonite, cf. Glyptoxoceras,
from the Smoky Hill Chalk (Santonian) of western In
June, 2008, the partial internal mold of a small ammonite was discovered beneath a Tylosaurus
nepaeolicus skull collected from the Clioscaphites vermiformis-C. choteauensis zone
(early to mid-Santonian), Smoky Hill Chalk. in northern Lane County, Kansas by staff of
the |
A brief background of Kansas ammonites from the Introduction of Everhart and Maltese, 2010:
"Cephalopods, including ammonites, occur in relative abundance in
several Late Cretaceous formations in Kansas, but are seldom observed or collected from
the Smoky Hill Chalk Member of the Niobrara Chalk due to the poor preservation of their
aragonitic shells (Hattin, 1982). Among the first to mention The calcitic aptychi of ammonites (Everhart, 2005, fig. 3.4) are preserved
occasionally at various stratigraphic levels in the chalk. Hattin (1982) noted that the
remains of cephalopods belonging to the Collignoniceratidae are rare and mostly only
represented by aptychi. Although there has been considerable debate over use of aptychi as
ammonite opercula or jaws (Morton, 1981), more recently it has been suggested by Lehmann
and Kulicki (2007) that they served as both operculum and cutting edges of the lower jaws.
In his description of the Niobrara vertebrate stratigraphy, Stewart (1990) designated two
of his biostratigraphic zones based on occurrence of Spinaptychus n.
sp. and Spinaptychus sternbergi, and noted occurrence of a third
form, Rugaptychus sp. in the Zone of Hesperornis (Early
Campanian). Another aptychi form (Spinaptychus n. sp. B; J.D. Stewart,
pers. comm. 1991) is present in the Zone of Protosphyraena perniciosa ( |
That said, I know barely enough about these invertebrates to be dangerous. So bear with me and I will show some of the specimens that I have collected or seen collected from Kansas rocks in the last five years. We'll start with the youngest Cretaceous rocks in Kansas (Pierre Shale Group) and go down in time to the oldest - the Kiowa Formation:
Other ammonite related sites:
The Geology of Portsdown Hill Ammonite page
Sharon Springs Formation (Pierre Shale Group) - Middle Campanian:
Ammonites occur rarely in the shales that overlie the Niobrara Formation in far-western Kansas. Baculites are more commonly collected there. I'll add pictures at a later date:
Smoky Hill Chalk Member of the Niobrara Chalk Formation - Upper Coniacian to Lower Campanian:
LEFT: The piece of chalk that preserves an impression (internal
mold) of a heteromorph ammonite (FHSM IP-1484). This is the first such specimen ever
collected from the Smoky Hill Chalk. The specimen was collected by Anthony Maltese in
northern Lane County. RIGHT: A close-up of IP-1484 showing the dark trace that indicates the probable location of the siphuncle in the living ammonite. The siphuncle is a living tube that passes from the body of the ammonite through each chamber of the ammonites shell. It allows the extraction of water from and the injection of gas into the otherwise closed off older chambers of the shell. This enables the ammonite to adjust the amount of water in the hollow shell compartments and allows the animal to control its buoyancy to a certain extent. In this preservation, the structure in the circle may represent the terminus of the siphuncle where it enters the living chamber. See another example below. |
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LEFT: The probable funnel shaped terminus of the siphuncle tube in FHSM IP-1484 RIGHT: An internal mold of Clioscaphites choteauensis from the middle of the Smoky Hill Chalk. According to Cobban, this is the only species of Scaphites found in the chalk. (About 4 in / 10 cm in diameter) |
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LEFT: A portion of the internal mold a "Texanites" ammonite from the Smoky Hill Chalk collected by Duffer Mauck of Hoxie, Kansas. Note that a portion of an associated aptychus is also preserved laying the ammonite mold. Ammonite shells were composed aragonite and were generally dissolved before they could be fossilized. The smaller and thinner aptychi, on the other hand, were composed of calcite and preserve very well, sometimes with exquisite detail (below). RIGHT: Another fragment of the same specimen. Photos by Mike Everhart, courtesy of J.D. Stewart. |
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Spinaptychus is the term used to describe the paired
structures (aptychi) that probably served as jaw structures for the ammonite (similar to
squid beaks). They look like the inside of a clam shell (smooth) on the inside while the
outside is covered with numerous, short projections or spines. Several types of "Spinaptychi"
are found in the chalk. LEFT: Spinaptychus sp.: An ammonite aptychi specimen (FHSM IP-528) on exhibit in the Sternberg Museum. Note this publication is available on the web: Fischer, A.G. and Fay, R.O. 1953. A spiny aptychus from the Cretaceous of Kansas. Bulletin Geological Survey Kansas. 102(2):77-92, 2 pl. RIGHT: A large ammonite aptychus - FHSM IP-941 |
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LEFT: A pair of aptychi (EPC 1994-13) that I
collected in 1994 from the lower chalk of Gove County (about 4 inches tall).
This specimen was prepared by Neal Larson (Black Hills Institute).
Close-up views of two other fragmentary specimens are HERE.
Note that these structures are rather thin and delicate, with thickness
that varies from 1 to 2 mm, except at the hinges where it is somewhat
thicker.
RIGHT: Another nice Spinaptychus sp. specimen (RMDRC 10-018) collected in 2010 from the lower chalk of Gove County by Anthony Maltese (Rocky Mountain Dinosaur Resource Center). This specimen was prepared, including minor reconstruction, by Neal Larson (Black Hills Institute). |
Blue Hill Shale Member of the Carlile Shale Formation - Upper Middle Turonian:
The Blue Hill Shale ammonite fauna is pretty much dominated by the occurrence of a large ammonite called Prionotropis hyatti (formally Collignoniceras hyatti) - See picture at top of this page -
LEFT: The outer coil of a Prionotropis hyatti ammonite
collected by Gail Pearson in March, 2010, from the Blue Hill Shale in southwestern
Mitchell County, KS. RIGHT: Part of the inner coil of a similarly-sized Prionotropis hyatti ammonite that I collected in March, 2010. Note the distinctive suture formed between adjacent chambers of the ammonite. Another example is shown HERE. Unfortunately the larger outer coil was only partially preserved. However, this fragment preserves the terminus of the siphuncle on the upper edge, just below the keel. Several smaller ammonites were preserved in the concretion that formed around this ammonite. |
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LEFT: Close-of the Prionotropis fragment showing the
terminus of the siphuncle. RIGHT: An anterior end view of one of the chambers, showing the terminus of the siphuncle just below the keel of the shell. |
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LEFT: The Blue Hill Shale also preserves smaller ammonites inside
"mud balls", small gray concretions about the size of a baseball.
Sometimes cracking them open with a hammer will reveal an ammonite or other shell
inside.... RIGHT: Another mud ball ammonite. |
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LEFT: Another ammonite preserved in a mud ball... these are
actually limestone concretions that formed around the ammonite on the muddy bottom of the
sea. RIGHT: A small Prionotropis hyatti ammonite preserved partially inside a mud ball concretion. In this case, outer edge of the ammonite was visible before the concretion was cracked open. |
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LEFT: A heterotroph ammonite and the counter-part that was broken
off to reveal it. In this case the ammonite is a species which was discovered first in
Kansas, called Scaphites carlilensis, for the Carlile Shale Formation. RIGHT: Another Scaphites carlilensis that still preserves some of the rainbow of colors in the nacre. |
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LEFT: Still another Scaphites carlilensis with slightly
different preservation. If you look at the right side of the shell, you can see that some
of the sutures are preserved. RIGHT: Another Scaphites carlilensis, but this one is preserved in the "red rock" layer that occurs about 3 m below the layer containing the mud balls. In this case, most of the original shiny nacre of the shell is preserved. |
Greenhorn Formation - Lower Turonian to Middle Cenomanian:
Kiowa Formation - Upper Albian (Early Cretaceous):
REFERENCES:
Carpenter, K. 2003. Vertebrate biostratigraphy of
the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale).
pp. 421-437 in Harries, P.J. (ed.), Approaches in High-Resolution Stratigraphic
Paleontology, Kluwer Academic Publishers, The
Cobban, W.A. 1951. Scaphitoid cephalopods of the
Niobrara Group.
Crampton, J.S. 2004. Shell composition, cryptic
costae, complex composite molds and taphonomic chicanery in Mytiloides (Inoceramidae,
Bivalvia). Journal of Paleontology 78(6):1091-1096.
Everhart, M.J. 2005. Oceans of
Everhart, M.J.
and Maltese, A. 2010. First report of a heteromorph ammonite, cf. Glyptoxoceras,
from the Smoky Hill Chalk (Santonian) of western
Green, R.G. 1977. Niobrarateuthis walkeri, a
new species of teuthid from the Upper Cretaceous Niobrara Formation of Kansas. Journal of
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Hattin, D.E. 1982. Stratigraphy and depositional
environment of the Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) of the type
area, western
Hasenmueller, W.A. and Hattin, D.E. 1985. Apatitic
connecting rings in moulds of Baculites sp. from the middle part of the Smoky Hill Member,
Niobrara Chalk (Santonian), of western
Jeletzky, J.A. 1955. Belemnitella praecursor,
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Miller, H.W. Jr. 1957. Belemnitella praecursor from
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Miller, H.W. 1969. Additions to the fauna of the
Niobrara Formation of Kansas.
Morrow, A.L. 1935. Cephalopods from the Upper
Cretaceous of
Morton, N. 1981. Aptychi: the myth of the ammonite
operculum. Lethaia 14(1):57-61.
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