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Uintacrinus calyx
These calyxes are in Uintacrinus slab on display in Keystone Gallery. The slab (shown at right) contains twenty calyxes.
Crinoids (kry-noidz) are invertebrate sea animals related to present-day sea urchins and brittle stars. They are very common fossils in Mississippian, Pennsylvanian and Permian deposits.

Crinoid slabThe crinoid genus found in the Kansas chalk, Uintacrinus, (you-in-tuh-cry-nuss) had no stem to attach itself to the seabed floor, unlike most crinoids. Therefore it could move freely from place to place.

Uintacrinus fed on microscopic sea life by moving it down feathery extensions on its four-foot-long segmented arms. The food ended up in the crinoid’s mouth under its calyx (kay-licks) or head. It is not certain if these crinoids were solitary or communal creatures, but they are often preserved in large colonies.

—Clams & Oysters—

By far the most numerous fossils found in the Niobrara Cretaceous are clams and oysters. The three main groupings of these shells are Inoceramids, Rudists and Oysters.


InoceramusThe largest of the many species of Inocermids is Inoceramus platinus. These clam shells could grow as large as four feet in length and width. They are often preserved with oyster shells on both sides.

Inoceramus-MuralInoceramus platinus (eye-no-serr-a-muss platt-in-uss) shells sometimes fossilize with small fish inside. It is not known why this occurs. The small fish may have sought refuge inside the clams or fed on small bits of food inside. Somehow they were trapped when the clam died.

This phenomenon provides paleontologists an excellent source of small fossil fish that otherwise would not have been preserved in a deep ocean environment. Two of the most common fish preserved in clams are Omosoma (oh-muh-so-muh), a small, herring-like fish and Kansius (kan-zee-uss), a fat-bodied, perch-like fish.


Other interesting clams from the Niobrara formation are the coral-shaped rudists. They are represented by the genus Durania (durr-ay-nee-uh) and are much more prevalent in the lower chalk, often occurring in groupings of as many as twenty individuals. Most Durania in the upper chalk are single or in small groups and are hard to find as they resemble pieces of calcite that occur in the chalk.

Like Inoceramus clams, Durania often have oyster shells adhered to them.

Ostrea congesta

Oysters are very common throughout the Niobrara chalk and you can hardly avoid walking on them in some locations. They are often packed into thick layers of large slabs. The name Ostrea congesta (oss-tree-uh kun-jess-tuh) was chosen for this species to describe this crowded grouping. Sometimes individual Ostrea are found and they are often adhered to various kinds of clams.


Ammonite-Mural Cephalopods may have been prevalent in the Kansas Cretaceous Sea. However, they did not fossilize very well because of the high lime content in the sediment.

Ammonites (amm-o-nights) (coiled-shell) and Baculites (back-you-lights) (straight shell) are only known in the Smoky Hill chalk from a portion of their shell. The aptichi (hood) that covers the opening of the squid’s shell was composed of material (calcite) that fossilized. Impressions of the rest of the shell may be preserved as a trace fossil. Aptichi come in relatively equal-sized, leaf-shaped pairs that resemble those of a bi-valve clam.

Spinaptychus & Rugaptychus

Spinaptychus (spine-app-tick-uss) is a cephalopod hood that has raised, sharp dots that cover its outer surface. Rugaptychus (rug-app-tick-uss) is similar to Spinptychus, but is usually smaller and more elongated in shape. Instead of raised dots, Rugaptychus has raised bands on its outer surface.

These aptychi are on display in Keystone Gallery. The two pairs on the left side of this image are Rugaptychus. The other aptychi are Spinaptychus.

Niobrarateuthis bonneri

Niobrarateuthis bonneri-MuralAnother cephalopod preserved in the Niobrara formation is the giant squid. The only parts of this soft-bodied animal that fossilize are the ink sac and pen. Squids use ink to hide when escaping other predators. One genus of squid pen found in the Kansas chalk is Niobrarateuthis bonneri, (nai-o-brer-a-tooth-iss baw-nurr-eye) found by and named for Marion Bonner.

©2015 Keystone Gallery / Photos © Barbara Shelton unless otherwise noted

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