A Field Guide to the Smoky Hill Chalk Part 1: Invertebrates  Copyright © 2000-2007 by Mike Everhart Last revised 08/14/2007         LEFT: A beautiful specimen of Uintacrinus socialis crinoids collected by Chuck Bonner and on display in the Keystone Gallery (about three feet across)

INVERTEBRATES: Besides being composed of microscopic fossils itself (coccolithophores and coccoliths of marine algae), the Smoky Hill Chalk contains many fossil remains of invertebrates (animals without backbones) including clams, crinoids and cephalopods (squids and ammonites). Other kinds of invertebrates that are found, but not well represented in the fossil record include sponges, cirripids, annelid worms and, rarely, crustaceans.

The Smoky Hill Chalk was deposited near the center of  the Western Interior Sea during late Cretaceous time (87-82 mya).   This map shows the extent of the seaway about 90 million years ago. (Map is part of the exhibits at the University of Nebraska State Museum, Lincoln, NE.) Although the Smoky Hill Chalk has been a excellent source of well preserved vertebrate remains, the preservation of invertebrates, except Inoceramid clams. oysters and rudists, is generally poor because much of the shell material (aragonite) was dissolved prior to fossilization.

Inoceramids: Some species of clams (bivalves) grew to giant size in the late Cretaceous, attaining diameters of four feet or more. In cross section, these shells are composed of prismatic (calcitic) crystals. The inner, nacreous (Mother of Pearl) layer of the shell was usually dissolved during fossilization and the outer portion is usually covered with colonies of oysters and other invertebrates. Pearls are occasionally found pressed into the Inoceramid shell.

Volviceramus grandis

LEFT: Volviceramus grandis - A common, large bivalve in the lower Smoky Hill chalk. This lower valve measures 12 inches by 10 inches. Click here for a view of the other side of this shell which is encrusted with Pseudoperna congesta oysters. RIGHT: A juvenile V. grandis lower valve with attached P. congesta oysters. This shell measures about 2.5 by 2.0 inches. The shell crushing shark, Ptychodus, most likely fed on shells that were about this size.

LEFT: A field photograph of a medium sized V. grandis shell that was uncrushed and shows the depth of the bowl shape. Specimen was found in the lower chalk of Trego County RIGHT: A field photograph of a complete V. grandis shell from the lower chalk of Trego County with the upper (right) valve still in place, and completely covered with Pseudoperna congesta oysters.   The bottom of this specimen was also completely covered with oysters.

Cladoceramus undulatoplicatus

Cladoceramus undulatoplicatus: A large fossil clam that occurs in a limited zone about 1/3 of the way up from the base of the chalk. The shell is characterized by deep ripples and has been called the "Snowshoe Clam." At right: The edge of a large Cladoceramus undulatoplicatus eroding from the edge of a gully in the lower Smoky Hill chalk.

Platyceramus platinus

: A very large clam shell that occurs throughout the chalk, sometimes reaching more than four feet in diameter. As the name implies, these shells are flat and often very thin. While alive, the interior sometimes served as shelter for schools of small fish which are occasionally preserved inside as fossils pressed into the shell. RIGHT: Part of a large Platyceramus platinus eroding from the middle of the Smoky Hill Chalk. (Scale = 6 in / 15 cm) LEFT:  The exhibit specimen of Platyceramus platinus (FHSM IP-532) at the Sternberg Museum. This shell is about 3 ft. wide and 3.5 feet long. (Scale = 10 cm)

LEFT: A very large P. platinus shell eroding from the lower chalk of Trego County. The shell is almost completely covered with Pseudoperna congesta oysters.  The shell is about 1 m (39 in.) across. RIGHT: Platyceramus platinus shells were so large that they provided shelter for schools of small fish. Sometimes the fish were trapped inside the clam's shell when it died.  This picture shows fragments of small fish that were preserved inside a Platyceramus platinus shell from the Smoky Hill Chalk.

Pseudoperna congesta (Oysters)

Small bivalve shells, similar to the oysters found in the ocean today, covered any solid object that they could attach to. Inoceramid clam shells, rudists, driftwood and the skeletons of marine reptiles served as homes for oysters and other invertebrates in the inland sea. Sometimes there were 3 or 4 layers as succeeding generations built up on the same shell. The lower, or right shell of the oyster is attached to the substrate. The other shell was free to open and close. The species found most often is called Pseudoperna congesta (Conrad, in Nicollet, 1843, p. 169): "*Conrad's description of the ostrea congesta: Elongated; upper valve flat; lower valve venticose, irregular; the umbo truncated by a mark of adhesion; resembles a little gryphea vomer of Morton." At right: Several small oysters on Inoceramid fragments and an unusual unattached oyster shell (upper right). Exogyra is a very rare and recently discovered, but unnamed species of oyster in the lower. (Hattin, 1995)

Rudists: A strange looking, highly modified clam that more or less floated on the surface of the mud. The lower shell looked like a large funnel or cone with a thick circular collar.

LEFT: Rudists (Durania maxima) had heavy  cone shaped shells, often with a large, circular collar. (From Hattin, 1988) The species found most often (Durania maxima) occurs most commonly in the lower 1/3 of the chalk. (See Hattin, 1988). The most common remains are pieces of heavy, finely striated shell. The upper or free valve of the clam has not been found preserved in the chalk.

LEFT: A beautiful example of a Durania maxima colony from the the Smoky Hill Chalk in the exhibits of the Sternberg Museum of Natural History. RIGHT: More often, the cones are found flattened and sometimes only circular rim remains.

Crinoids (Uintacrinus socialis) - "Their bodies were about the shape of half an egg, with an opening in the center, and ten arms radiating from the margin. These arms were three feet long, with feathered edges. Over the mouth, too, were smaller arms used to comb off into the mouth the tiny animal life of the sea, that was strained through, and caught in the meshes of the feathered arms. My boys found hundreds of these crinoids in the Chalk on Beaver Creek, Kansas, called Uintacrinus socialis. We enriched many Museums with them."

Excerpted from Charles H. Sternberg's "Hunting Dinosaurs on the Red Deer River, Alberta, Canada" (1917, p. 156).  

Crinoids (related to starfish and sea urchins) occurred as floating colonies. The preserved colonies are found rarely near the middle of the Smoky Hill chalk formation. There are good examples in the Sternberg and at the Museum of Natural History at the University of Kansas. At right: A portion of a slab containing dozens of Uintacrinus socialis crinoids. This specimen is in the KU Museum of Natural History. LEFT: A detail from the exhibit specimen of Uintacrinus socialis at the Sternberg Museum. See close-ups of other individuals in this slab: HERE, HERE and HERE.

Cephalopods:

LEFT: A detail from the undersea painting in the Sternberg Museum showing what an living ammonite may have looked like. Ammonites were creatures that resembled a squid or octopus living inside the coiled shell of a large snail. They swam backwards the ocean using a jet of water from their siphons to propel them. The coiled shells are only rarely preserved in the chalk but other fossil evidence indicates that they lived in the Western Interior Sea. Go here for more information about ammonites.  RIGHT: A specimen of Placenticeras meeki in the collection of the University of Nebraska State Museum.

	LEFT: The markings and shapes of ammonite shells are very distinctive to species.  This enables the shells to be used as stratigraphic markers in those rocks that preserve them. RIGHT: An ammonite shell in the Sternberg Museum exhibit.  The blue marks indicate two or more series of depressions in the ammonite shell that have been interpreted to be bite marks. Some researchers believe that "tooth marks" found  in ammonite shells indicate that they may have been prey for mosasaurs and other large predators.
	LEFT: An external mold of Clioscaphites choteauensis from the middle of the Smoky Hill Chalk. According to William Cobban, this is the only species of Scaphites found in the chalk. (About 4 in / 10 cm in diameter) RIGHT: A very rare fragment of an ammonite cast (Texanites sp.) from the Smoky Hill chalk from a specimen about 18 inches in diameter. Ammonites were apparently abundant during the deposition of the Smoky Hill chalk but their shells were seldom preserved.

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.

The delicate aptychi that served as the jaws of the ammonite are well preserved in the Smoky Hill chalk (About 4 inches tall). Click here for a picture of another specimen at the Sternberg Museum (FHSM IP-528). Note this publication on the web: Fischer, A. G. and R. O. Fay., 1953. A spiny aptychus from the Cretaceous of Kansas. Bulletin Geological Survey Kansas. 102(2):77-92, 2 pl.

Squid (Teuthids): Squid are soft bodied invertebrates that probably occurred in great abundance in the warm oceans during this period. Occasionally, the internal structure (gladius or pen) of the squid is preserved. These fossils are characterized by long, straight fibers or strands that often appear to be iridescent.  Squid remains were were initially mistaken for an unusual fish bone.  CLICK HERE FOR MORE INFORMATION

Tusoteuthis, a 'giant' squid that lived in the Western Interior Sea, may have been as long as 25 ft. (7.5 m).  The evidence of bite marks in some squid pens shows that squid were eaten by many predators including fish and mosasaurs. Click here for a picture of a very large Tusoteuthis longa fossil in the Museum of Geology at the University of Kansas. LEFT: A fossilized squid pen (Tusoteuthis longa) in the exhibit at the Sternberg Museum of Natural History.

LEFT: An artist's idea of what the Late Cretaceous squid, Tusoteuthis longa Logan may have looked like (Sternberg Museum). Click here for a picture of a fish specimen (Cimolichthys) that died with a squid in its mouth.

Other Invertebrates: Many invertebrates that were living in the inland sea are represented indirectly by casts, burrows and other evidence. In some cases, the damage done by cirripids as they bored into Inoceramid shells is preserved while the actual animal is not. In addition, the bottom muds of the inland sea may have been relatively low in oxygen and may have not supported large numbers of invertebrates. There is still much work to be done in defining the invertebrate community of the inland sea.

Continued on next page..................  A Field Guide to Fossils of the Smoky Hill Chalk - Part 2; Sharks and Bony Fish

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