A Field Guide to the Smoky Hill Chalk

Part 1: Invertebrates

Copyright © 2000-2013 by Mike Everhart

Last revised 11/11/2013

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 mostly composed of microscopic fossils itself (coccolithophores and coccoliths of marine algae), the Smoky Hill Chalk contains the remains of many 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 (Late Coniacian-Early Campanian; 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. This includes the nacre of most shells and the shiny coating of fossil pearls.

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. According to Sowerby 1823, Inoceramus means "fibrous shell," describing the prisms that are visible on shell fragments. Inoceramus cuvieri was the first species of Inoceramus that was formally described.

James Parkinson (1811b) wrote one of the first descriptions of an inoceramid shell:

"Fragments of thick shell of a fibrous structure: The doubts expressed respecting the nature of this shell, and the observations made with regard to it, offer another strong point of agreement between the shells of the two strata. The shell here alluded to is most probably that represented Org. Rem. vol. III. pl. V.-fig. 3; the structure of which agrees exactly with that mentioned as found in the French stratum of- chalk. That shell is however described as being of a tubular form; it is therefore right to observe, that fossil pinnae do sometimes possess this peculiar structure."

LEFT: Figure 3 from Plate V in Parkinson's Organic Remains of a Former World (1811a).

Parkinson, J. 1811a. Organic Remains of a Former World – An Examination of the Mineralized Remains of the Vegetables and Animals of the Antediluvian World. Vol III, Whittingham and Roland, London, i-xv, 479 pp., plates I-XII, index.

Parkinson, J. 1811b. Observations on some of the strata in the neighborhood of London , and on the fossil remains contained in them. Transactions of the Geological Society of London 1(XIV):324-354.

LEFT: A drawing of Inoceramus cuvieri Sowerby (1814) from Great Britain as figured in Sowerby and Sowerby (1823). I. cuvieri is fairly common in the Greenhorn and Carlile (Turonian) formations in Kansas, but I had never paid much attention to it. In late 2011, I needed the citation for the name given by Sowerby and discovered that it wasn't really that easy to find. In fact the first citation that I worked with was incredibly wrong. The citation pointed back to seven volumes of a book written by Sowerby between 1812 and 1843 called "The mineral conchology of Great Britain , or colored figures and descriptions of those remains of testaceous animals or shells, which have been preserved at various times and depths in the Earth." ... After some searching, I found Inoceramus cuvieri described and figured (left) in Volume 5, but the volume had been published in 1823, not 1814. So I kept looking. The solution to the mystery was found on page 457 of a paper published by James Sowerby in 1822:

Sowerby, J. 1822. On a fossil shell of a fibrous structure, the fragments of which occur abundantly in the chalk strata and in the flints accompanying it. Transactions of the Linnean Society of London XIII: 453-458. Plate XXV.

LEFT: A note at the beginning of the paper states that it had been read orally by (James Sowerby (1757-1822) before the meeting of the society on November 1, 1814. There was no explanation of the delay in publication. His son, James De Carle Sowerby (1787-1871) continued the publication of the conchology books starting with Volume 5. Volume 7 was never finished.

LEFT: It is worth noting that about the same time, Cuvier described a similar species from France, and indicating that it differed from Inoceramus in some ways, but also credited the work of Sowerby and James Parkinson (Cuvier, G. and Brongniart, A. 1822. Description Géologique des Environs de Paris):

"Fig.10, A, E, F, G, H, I. Catillus cuvieri, A. BR. (p.15) Inoceramus cuvieri, SOW., PARK. The name Inoceramus has been given to shells which seem to me show so numerous and striking differences that I could not decide to keep them together, breaking the law I imposed myself to bring no change in the shells division (family), such as it had been established by the specialists. One has just to compare the fossil shells that I unite here under the name of Catillus with Inoceramus, fig.11 and 12, pl.VI, to be stricken by this difference. The species of both these genera are found in the chalk, but they are located in very distant strata.

It has seemed logical for me to keep the name Inoceramus for the gender composed of the shells that M. Parkinson made known and drew under this name in the first volume of the Transactions of Geol. Soc. of London., that M. Sowerby established and presented under this same name et the Linnaean Soc. of London in 1814, of which figures he just published in plates 305 and 306 in Conchology, and I have preferred give a new name to the species for which I see no description nor precise figure anywhere.

I haven't yet seen an entire individual of this species, so that the gender itself is difficult to characterize; but with the help of hinge fragments from various collections, with the figures published by MM. Parkinson and Mantell, one can succeed in characterizing satisfactorily this gender so as it can be recognized by geologists, and give them a way to designate in a uniform manner so remarkable a shell commonly found in the white chalk." (Translation by Jean-Michel Benoit)

Volviceramus grandis (Late Coniacian)

Volviceramus grandis: A common clam found in the lower third (late Coniacian) of the chalk. The lower shells are thick and generally bowl shaped. In many areas, the surface of the chalk is littered with thousands of fragments of this shell, some of which may resemble bone in outward appearance. Examination of the edge of the fragment will determine if it is bone (porous) or shell (crystalline structure).

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 relatively 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 (Early Santonian)

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 (above Marker Unit 7). This zone straddles the boundary between the Coniacian and Santonian ages. The shell of Cladoceramus undulatoplicatus is characterized by deep ripples and it has been referred to as the "Snowshoe Clam."

LEFT: The broken edge of a large Cladoceramus undulatoplicatus eroding from the edge of a gully in the lower Smoky Hill chalk. This specimen was associated with the discovery of a Pteranodon sternbergi skull. in 1996.

RIGHT: Another large Cladoceramus undulatoplicatus eroding from the lower Smoky Hill chalk. This specimen was associated with the discovery of a Ptychodus mortoni specimen (FHSM VP-14785).

Platyceramus platinus (Latest Coniacian through Early Campanian):

A very large clam shell that occurs throughout the chalk, sometimes reaching more than four feet in diameter in Kansas. They are thought to be the largest clams ever, reaching nearly 9 feet in length (3-4' width) in the Niobrara of Colorado (see Kauffman, et al, 2007). As the name implies, these shells are relatively 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.

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)

The latest publication on these giant clams is:

Kauffman, E.G., Harries, P.J., Meyer, C., Villamil, T., Arango, C. and Jaecks, G. 2007. Paleoecology of giant Inoceramidae (Platyceramus) on a Santonian seafloor in Colorado. Journal of Paleontology 81(1):64-81.

LEFT: Part of a large Platyceramus platinus eroding from the middle of the Smoky Hill Chalk. (Scale = 6 in / 15 cm). There has been some controversy regarding the orientation of these clams as they sat on the sea bottom because oysters (Pseudoperna congesta) have been found on both sides. Stewart (1990) suggested that they sat upright, something like modern giant clams are found in modern coral reefs. Others (Kauffman, et al., 2007) indicate that they usually occurred in a recumbent mode, with the left valve on the sea floor. Since the shells are somewhat bowl shaped, this would allow oysters to colonize the lower portion around the edges. Otherwise, the shell could have been colonized after it had died and been turned over (although it is unknown "how" it would have been turned over).

RIGHT: My concept of a giant (> 1m) Platyceramus platinus resting on the sea floor with a rather large area of the rim of the lower shell exposed above the sediment... a great location for oysters looking for a home.

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 skeletal fragments of small fish that were preserved inside a Platyceramus platinus shell from the Smoky Hill Chalk.

How to collect a giant clam shell by Charles H. Sternberg (pp. 24-25, Sternberg, C.H. 1917. Hunting Dinosaurs in the Badlands of the Red Deer River, Alberta, Canada. Published by the author, San Diego, Calif., 261 pp.)

Here, too, in the [AMNH] Invertebrate Department, is the great Inoceramus shell 3'4"x3'7" in size. The second shell of these huge dimensions I sent to Tübingen University. Although they strew the rocks of the Kansas chalk in great numbers, they are always broken into small pieces, and these are scattered by the winds of heaven. It seems impossible to preserve them. But George [his son] and I learned the secret, and after finding a shell with· lips or hinge exposed, we carefully removed the loose chalk above it, then put a frame of two by four lumber around it, in which we poured plaster. On hardening thus stuck securely to the shattered shell, holding the fragments in place. Then we dug beneath and turned over the panel, and in the shop removed the chalk, leaving one side of the shell exposed in the solid plaster.

Pseudoperna congesta (Oysters)

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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."

LEFT: 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 Smoky Hill Chalk. (Hattin, 1995

Rudists: A strange looking, highly modified clam that more or less floated on the surface of the bottom 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). However, this Durania fragment was collected at the contact between the Smoky Hill Chalk and the overlying Pierre Shale (Early Campanian).

The most common remains are pieces of heavy, finely striated shell. The upper or free valve of the clam is composed of aragonite and has not been found preserved in the chalk.

RIGHT: A beautiful example of a Durania maxima colony from the the Niobrara Chalk in the exhibits of the Sternberg Museum of Natural History.

LEFT: The upper portion (expanded collar) of a Durania shell collected in southeastern Gove County. More often, the cone shaped shells of Durania maxima are found flattened and sometimes only circular rim remains.

RIGHT: Upper and lower views of another recently discovered solitary Durania maxima from the lower Smoky Hill Chalk of southeastern Gove County.

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.

LEFT: A portion of a slab containing dozens of Uintacrinus socialis crinoids. This specimen is in the KU Museum of Natural History. No, the dark spots are NOT eyes....

RIGHT: 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 - Ammonites:

See the new Kansas Ammonites page HERE

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.

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: The impression left by a large ammonite (FHSM AC-12029-2) collected in northwestern Rooks County, Kansas. Miller (1968) initially indentified this specimen as *“Brevahites? sp. B”* *in the Sternberg Museum collection. It was subsequently referred to Submortoniceras sp.* by Miller 1969. Ammonites were apparently abundant during the deposition of the Smoky Hill chalk but their shells were seldom preserved.** RIGHT: A very rare fragment of an ammonite cast (Texanites sp.) from the Smoky Hill chalk that would have come from a living specimen about 18 inches in diameter. Note that the paired aptychi (see photos below) are preserved on this fragment. Another fragment is shown HERE.
	LEFT: An external 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). RIGHT: Another view of the same specimen, with a scale (cm)
	LEFT: The impression of a heteromorph (not coiled) ammonite discovered in the Smoky Hill Chalk by Anthony Maltese in Lane County, KS. This is the only known example of this kind of ammonite in the chalk. The dark line probably represents the siphuncle. Featured on the new Kansas Ammonites page HERE RIGHT: Detail of the opening of the siphuncle. See: Everhart, M.J. and Maltese, A. 2010. First report of a heteromorph ammonite, cf. Glyptoxoceras, from the Smoky Hill Chalk (Santonian) of western Kansas, and a brief review of Niobrara cephalopods. Kansas Academy of Science, Transactions 113:(1-2):64-70.

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..

RIGHT: A large ammonite aptychus in the collection of the Sternberg Museum - FHSM IP-941.

Note this publication is available 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.

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).

LEFT: A pair of small ammonite aptychi (RMDRC 07-025) as found from the upper chalk of Logan County. Their small size could indicate that they are from a straight-shelled baculite, or just a small ammonite.

RIGHT: Another view of the same pair of aptychi... with a scale.

Belemnites and Baculites - Belemnites are an extinct group of marine cephalopods, similar in many ways to modern squid and more closely related to modern cuttlefish. Like squid, cuttlefish and octopi, belemnites possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length. The name "belemnite" is derived from the Greek word belemnon meaning "a dart or arrow."

Baculites is a genus of extinct, straight-shelled marine cephalopods. They are classed as a kind of heteromorph ammonite (see above) and lived in the oceans worldwide throughout the Late Cretaceous Period.

In his paper on the Kansas Niobrara, Williston (1897) also noted that baculites had never been collected from the chalk, but indicated that Baculites ovatus had been found in the overlying Pierre Shale near McAllister Butte in western Logan County . Morrow (1935, pl. 53, fig. 7) was the first to describe and figure the internal mold of a baculite (Baculites sp. cf. B. ovatus) from chalk of Trego County . Since that time the molds of baculites have been recognized by several authors (Miller 1968, 1969; Hattin 1982; Hasenmueller and Hattin, 1985; Stewart 1990).

Based on a single, damaged specimen in the University of Kansas collection, Jeletzky (1955) reported on the first belemnite from the Smoky Hill Chalk which he identified as Belemnitella praecursor. Two years later, Miller (1957) also described Belemnitella praecursor from 12 specimens collected by G.F. Sternberg and M.V. Walker. Those specimens apparently had not been available to Jeletzky. Following Miller’s publication, Jeletzky (1961) was able to examine the material in the collection of the Sternberg Museum , and subsequently redescribed them as belonging to the genus Actinocamax, including two new species, A. sternbergi and A. walkeri. Hattin (1982) mentions that belemnites are rare in the chalk, but did not figure them.

Like squid, belemnites have a kind of internal skeleton or shell that is composed of fibrous calcite. A complete belemnite shell consists of three parts; however, the fossil that is most normally collected is called the guard (or rostrum). It is the posterior part of the shell that was originally located in the tail of the belemnite. The guard is elongated and bullet-shaped, cylindrical and usually pointed at one end. The sharp end points towards the rear of the belemnite. The guard is usually translucent and is amber or coffee-colored. (Additional information HERE)

LEFT: Two views ofFHSM IP-699 belemnite in the Sternberg Museum collection.

RIGHT: FHSM IP-705 belemnite in the Sternberg Museum collection.

LEFT: Two views of FHSM IP-706 belemnite in the Sternberg Museum collection.

RIGHT: FHSM IP-707 belemnite on exhibit in the Sternberg Museum.

Baculites are rarely preserved in the Smoky Hill Chalk. Like ammonites, their shells are composed of aragonite which usually dissolves before it can be preserved.

LEFT: A specimen of Baculites maclearni from a concretion in the Sharon Springs Member (Middle Campanian) of the Pierre Shale in western Logan County.

RIGHT: A second specimen of Baculites maclearni from a concretion in the Sharon Springs Member (Middle Campanian) of the Pierre Shale in western Logan County. This photo clearly shows the sutures between the segments of the shell.

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 are sometimes 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 drawing of the type specimen of Tusoteuthis longus Logan 1898 (Plate CX, Figure 2). Note that the species name was corrected for gender to longa by Miller (1868).

Logan, W.N. 1898. The invertebrates of the Benton, Niobrara and Fort Pierre groups. The University Geological Survey of Kansas, Part VIII, 4:432-518, pl. LXXXVI-CXX.

Miller, H.W., Jr., 1968. Invertebrate fauna and environment of deposition of the Niobrara (Cretaceous) of Kansas. Fort Hays Studies, n. s., science series no.8, i-vi, 90 pp.

	LEFT: A fossilized squid pen of Tusoteuthis longa (FHSM IP-710) in the exhibit at the Sternberg Museum of Natural History. This specimen was collected by Marion Bonner in Logan County. Squid pens (rachis) are made up of chitin, not bone or cartilage. RIGHT: The gladius of the type specimen of "Enchoteuthis melanae" (FHSM IP-13049) discovered by and named for Melanie Bonner. This specimen appears to preserve much of the original chitin...
	LEFT: A nearly complete Tusoteuthis squid pen collected by Scott Garrett from Trego County in 2009. Note that the missing pieces looks suspiciously like the bite marks left by a small shark. *RIGHT: A field shot of a partial squid pen of Tusoteuthis longa* that I collected in May, 2010. A fragment of a inoceramid shell was laying across the gladius.**

LEFT: Four views of a squid pen that was bitten through by an unknown predator.

Click here for a picture of a fish specimen (Cimolichthys) that died with a squid in its mouth.

RIGHT: An artist's reconstruction of what the Late Cretaceous squid, Tusoteuthis longa Logan may have looked like (Sternberg Museum).

Cirripeds (Families Scalpellidae and Stramentidae)

Cirripeds are any of various crustaceans of the subclass Cirripedia, which includes the barnacles and related organisms that attach themselves to objects or become parasitic in the adult stage.

LEFT: Upper Cretaceous stalked cirripids (adapted from Hattin 1977) are often found attached to inoceramid shells. .

RIGHT: A partially disassociated cirriped (Stramentum haworthi) from the Fairport Chalk of Russell County, KS.

For more information:
Williston, S.W. 1897. The Kansas Niobrara Cretaceous. The University Geological Survey of Kansas 2:237-246, pl. XXXV.
Logan, W.N. 1897. Some new Cirriped crustaceans from the Niobrara Cretaceous of Kansas. Kansas University Quarterly 6(4)187-189.
Stevenson, R.E. 1979. Attachment sites of a stalked cirriped in the Cretaceous Niobrara Sea. Proceedings South Dakota Academy of Science 58:21-29.

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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