Natural History, 2001 Colorado Blvd., Denver, CO 80205. P.J. Harries (ed.) ... Fort Wallace in western Kansas (see Almy, 1987, for a history of the discovery).
Chapter 11
Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale) KENNETH CARPENTER
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. History of Collecting Fossil Vertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Vertebrate Biostratigraphy of The Smoky Hill Chalk And Sharon Springs Member . 3.1. Protosphyraena pernicosa Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Spinaptychus n. sp. Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Cladoceramus undulatoplicatus Zone . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Clioscaphites vermiformis and Clioscaphites choteauensis Zone . . . . . . 3.5. Spinaptychus sternbergi Zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6. Hesperornis Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7. Dolichorhynchops Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.
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INTRODUCTION Throughout much of the Western Interior of North America there is a
KENNETH CARPENTER • Department of Earth and Space Sciences, Denver Museum of Natural History, 2001 Colorado Blvd., Denver, CO 80205.
P.J. Harries (ed.), High-Resolution Approaches in Stratigraphic Paleontology. © Springer Science + Business Media B.V. 2008
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thick sequence of Upper Cretaceous marine rocks, which in places exceeds 6000 m (Weimer 1983). These sediments record a meridional seaway that connected the Gulf of Mexico to the Arctic Ocean during the Late Cretaceous. Marine vertebrate fossils are extremely common in some of these beds, especially in the Smoky Hill Chalk Member of the Niobrara Formation and in the overlying Sharon Springs Member of the Pierre Shale. Most specimen collecting has concentrated on the Smoky Hill Chalk because of the exquisite quality of the fossils. As a result, there is a large volume of literature that spans over 100 years (e.g., Cope 1875; Williston 1906; Goody 1970). Unfortunately, however, most collections have treated the Smoky Hill as a single fauna, despite early evidence to the contrary (e.g., Williston 1897). Recently, attempts have been undertaken to determine the biostratigraphic distribution of the various vertebrate taxa (Stewart 1988, 1990a; Bennett 1990, 2000; Sheldon 1996; Everhart 2001) and this has provided insights into the faunal changes that have occurred (Carpenter 1990, 1996a, also below; Sheldon 1996). The Smoky Hill Chalk has been extensively studied by Hattin (1982) in western Kansas, where it ranges from Upper Coniacian to Lower Campanian (~87.3-80.64 Mya; Kauffman et al., 1993), and the studies of Bennett (2000), Sheldon (1996) as well as Everhart (2001) rely on the marker units identified by Hattin (1982). He discovered 23 marker units (mostly bentonite seams or beds of distinctive lithology) in a 181.8 m composite section of the Smoky Hill Chalk. The Sharon Springs Member has been studied by Gill and Cobban (1966) in eastern Wyoming and by Gill et al. (1972) in western Kansas. The Sharon Springs Member is both older and younger in Kansas (~80.64-77 Mya based on ammonites, Kauffman et al., 1993) than in Wyoming (80.57-78.25 Mya based on ammonites, Kauffman et al., 1993). This age difference is due to the Sharon Springs deposition environment developing first and terminating last in what is now the Kansas region (Gill et al., 1972). The Sharon Springs Member is thinner than the chalk, being 38.7 m thick in Wyoming and 68.6 m thick in Kansas. Although the Sharon Springs has many bentonitic marker units (Gill et al., 1972), deposition was of such short duration that little change occurs in the vertebrate fauna (Carpenter, 1990, 1996a, and below). The contact between the Smoky Hill Chalk and the Sharon Springs Member is best seen in western Kansas, where it is gradational (Gill et al., 1972; Hattin 1982). In eastern Wyoming, the Sharon Springs is separated from the Smoky Hill Chalk by the Gammon Ferruginous Member. This member is chronostratigraphically equivalent to the top of the Smoky Hill Chalk and basal Sharon Springs of Kansas (Gill et al., 1972, fig. 3).
Late Cretaceous Vertebrate Biostratigraphy
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HISTORY OF COLLECTING FOSSIL VERTEBRATES
It is not known when the first fossil vertebrates were collected from the Smoky Hill Chalk or the Sharon Springs Member. Considering that bone often erodes out of the exposures, it seems probable that Native Americans were the first collectors. One of the first specimens collected for scientific study was an upper jaw fragment of a fish that was collected in 1803 by the Lewis and Clark Expedition. The jaw is believed to have been found in Smoky Hill Chalk exposures in what is now northeastern Nebraska. It was named Saurocephalus lanciformis by Richard Harlan in 1824, who compared it to an ichthyosaur, a marine reptile. In 1868, E. D. Cope, of The Academy of Natural Science of Philadelphia, received a fragmentary reptile skeleton from Captain Theophilus Turner, a U. S. Army surgeon stationed at Fort Wallace in western Kansas (see Almy, 1987, for a history of the discovery). Cope described the specimen as the long-necked plesiosaur, Elasmosaurus platyurus (Cope 1869, 1871). Much of the specimen was articulated in marked contrast to most of the Cretaceous vertebrate fossils that were being described from southern New Jersey. Thus alerted to the presence of articulated material in the West, Cope and O. C. Marsh of Yale University led expeditions to Kansas beginning in 1870. Numerous specimens of fish, reptiles and aquatic birds were collected and named, albeit most of the specimens were fragmentary because collecting techniques had not reached the level of sophistication developed only a decade later. Most of the specimens came from the Smoky Hill Chalk where preservation is better than the selenite encrusted bones of the Sharon Springs Member. For a variety of reasons, both men later hired others to continue to collect on their behalf: Benjamin Mudge and Samuel Williston for Marsh, and Charles Sternberg for Cope. Based in part on the scientific papers generated by Marsh and Cope during the 1870s and 1880s on the specimens, other museums and universities expressed an interest in acquiring specimens. Williston began collecting in 1890 for the University of Kansas many years after he left Marsh’s employment. The University has continued to collect from both the Smoky Hill Chalk and Sharon Springs Member sporadically since that time. In the 1880s, Cope financial difficulties forced Sternberg to become a freelance collector for other museums, mostly in Europe and Canada. Barnum Brown led American Museum of Natural History expeditions in 1903 and 1904 to Kansas, Wyoming and South Dakota where they collected in the Smoky Hill Chalk and the Sharon Springs Member (Carpenter, 1996a). Fredrick Loomis from Amherst College also collected from the Sharon Springs Member in Wyoming in 1903 (Loomis, 1915).
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In 1948, David Dunkle, from the National Museum of Natural History, made a collection from the Sharon Springs Member in eastern Wyoming (Gill and Cobban, 1966). He returned in 1973 for the Cleveland Museum of Natural History and made another small collection. Yet another large collection of vertebrates from the area was made by amateur paleontologists Asa Maxson and James Mellinger. These collections were transferred to the University of Colorado Museum in 1973. The University of Nebraska State Museum collected from the Sharon Springs Member in northwestern Nebraska beginning in 1966 (Martin and Tate, 1967). Further collecting from the area continued during the 1970s by the University of Kansas under the leadership of Larry Martin (S. C. Bennett, pers. comm., 1990). In 1967, the Field Museum of Natural History collected from the Sharon Springs Member near Fairburn, South Dakota. The South Dakota School of Mines has also collected sporadically for many years from near Fairburn, Buffalo Gap and several other localities in western South Dakota (Welles and Bump 1949). More recently, J. Martin (pers. comm., 1989) has begun more systematic collecting in South Dakota. The specimens collected from the Smoky Hill Chalk and Sharon Springs Member have been described in an enormous body of literature, the most notable of which are fishes by Stewart (1899, 1900), Bardack (1965, 1976), Bardack and Sprinkle (1969), Goody (1970, 1976), Stewart (1988); mosasaurs by Cope (1871) Williston (1898), Russell (1967); sea turtles by Cope (1873), Hay (1905), Zangerl (1953a, b), pterosaurs by Eaton (1910), Miller (1972), Bennett (1994), plesiosaurs by Williston (1903), Welles (1952, 1962), Welles and Bump (1949), Carpenter (1996b, 1997, 1999), and birds by Marsh (1880) and Martin and Tate (1976).
3.
VERTEBRATE BIOSTRATIGRAPHY OF THE SMOKY HILL CHALK AND SHARON SPRINGS MEMBER
The number of vertebrate specimens seen per square kilometer of outcrop in the Sharon Springs Member equals or exceeded that for the Smoky Hill Chalk in western Kansas (Carpenter 1996a). However, these specimens have not attracted as much attention because of encrustation and damage by selenite crystals. Only bones recovered from concretions are undamaged by selenite growth. Deep excavations into the Sharon Springs Member have demonstrated that selenite growth is a weathering phenomenon (Gill and Cobban, 1966; Carpenter 1996a) resulting in the dissolution of pyrite and the recombination of the liberated sulfur with carbonate in the weathered zone.
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Stewart (1990a) identified six biostratigraphic zones within the Smoky Hill Chalk Member, to which a new one, the Dolichorhynchops zone may be added for the Sharon Springs Member. The zones of Stewart (1990a) were created because many of the standard macrofossils used in zonation of the Western Interior are poorly preserved in the Chalk. This problem is especially true for ammonite shells as noted by Hattin (1982), but not for their aptychi (J. D. Stewart, pers. comm.). The Dolichorhynchops zone is used for convenience because ammonite preservation in the Sharon Springs Member is generally very poor due to selenite growth. Concretions, in which well-preserved ammonites occur, are generally spotty or restricted to specific horizons. The distribution of vertebrate taxa within the zones of the Smoky Hill Chalk and Sharon Springs Member is shown in Table 1 and graphically in Figure 1. The dinosaurs Niobrarasaurus colei and Claosaurus agilis are also included in Table 1 for completeness, but were not included in Figure 1 because these erratics are carcasses that had drifted to sea and are not part of the normal marine community. Pteranodon and several bird taxa are included because they were apparently all piscivores and lived hundreds of miles from land. For some taxa, the various zones represent their first appearance datum (FAD) or last appearance datum (LAD). In addition, some taxa are limited to a single zone, which may indicate endemism. The age of zones is based on cross-correlating the zones of Stewart (1990a) with Hattin (1982), and Hattin (1982) with Kauffman et al. (1993). As a result, the lower part of the Smoky Hill Chalk is now considered older than reported by Stewart (1990a) or Hattin (1982), and the Sharon Springs younger. Vertebrate fossils are not well known from the Fort Hays Limestone Member underlying the Smoky Hill Chalk Member. A few taxa are mentioned by Stewart (1990a): Ptychodus mortoni, Squalicorx, Cretoxyrhina, and Cretolamna, and these also occur higher in the Smoky Hill Chalk. Several partial fish skeletons have been collected from a quarry near Lyons, Colorado, and are housed at the Denver Museum of Natural History. They have yet to be studied, however.
3.1
Protosphyraena pernicosa Zone
This zone is named for a fish whose remains are moderately abundant and distinctive. Of the 34 vertebrate taxa in this zone, seven fish and one reptile taxa do not occur higher than the top of the P. pernicosa zone. An additional 20 fish, five reptiles and a bird extend into younger zones in the
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marker units of Hattin (1982) Scapanorhynchus rhaphiodon Ptychodus martini Belonostomus sp. Micropycnodon kansasensis Lepisosteus sp. Protosphyraena pernicosa Bananogmius zitteli Chelosphargis advena Pseudocorax laevis Ptychodus anonymous Martinichthyes ziphoides Protosphyraena nitida cf. “Macropoma” sp. Ichthyornis cf. I. anceps Enchodus dirus Paraliodesmus guadagnii Squalicorx falcatus
Protosphyraena pernicosa
biostratigraphic zones of Stewart (1990) modified
Inoceramus (Volviceramus) grandis
standard Kansas biostratigraphic zones (Hattin 1982)
Clioscaphites choteauensis
Table 1. Biostratigraphic distribution of vertebrates in the Smoky Hill Chalk, Niobrara Formation, and Sharon Springs Member, Pierre Shale.
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Late Cretaceous Vertebrate Biostratigraphy Pychodus mortoni Pteranodon sternbergi Niobrarasaurus colei Ichthyornis sp. “Pachyrhizodus” leptopsis Pseudocorax falcatus Urenchelys abditus Caproberyx sp. Trachichthyoides sp. Laminospondylus transversus Clidastes liodontus Tylosaurus nepaeolicus Kansius sternbergi Pteranodon longiceps Bananogmius evolutus Bananogmius favirostris Leptecodon rectus Osmosoma garretti Bothremys barberi Ectenosaurus clidastoides Claosaurus agilis Nyctosaurus gracilis Parahesperornis alexi Ichthyornis victor Cretoxyrhina mantelli Apsopelix anglicus Platecarpus planifrons Protosphyraena tenuis Apteodus sp. Enchodus shumardi Rhinobatus incertus Hadrodus marshi Protostega gigas ?Lophochelys natatrix ?Ctenochelys stenopora Polycotylus latipinnis Baptornis advenus Apatornis celer Ichthyornis dispar Cretolamna appendiculata Xiphactinus audax
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428 Ichthyodectes ctenodon Gillicus arctuatus Saurodon leanus Pachyrhizodus minimus Cimolichthyes nepaholica Pachyrhizodus caninus Enchodus petrosus Enchodus gladiolus Toxochelys latiremis Protosphyranea gladius Stratodus apicalis Clidastes propython Platecarpus tympanicus Tylosaurus proriger “Saurodon” pygmaeus Styxosaurus snowii Squalicorax cf. aff. S. kaupi Saurocephalus lanciformis Dolichorhynchops osborni Hydralmosaurus serpentinus Hesperornis regalis cf. Sphenocephalus sp. Globidens dakotensis Plioplatecarpus cf. P. primaevus Elasmosaurus platyurus Pteranodon n. sp.
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Smoky Hill Chalk. Lepisosteus is primarily a freshwater fish and its presence in marine strata is at odds with its normal lifestyle. The age of the P. pernicosa zone is lower Upper Coniacian. LAD: Scapanorhynchus rhaphiodon, Ptychodus martini, Micropycnodon kansasensis. FAD: Protosphyraena nitida, Belonostomus sp., Paraliodesmus guadagnii, Martinichthys ziphoides, Toxochelys latiremis.
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Figure 1. Diversity of vertebrate taxa by biostratigraphic zone. Abbreviations: Pp = Protosphyraena pernicosa; S = Spinaptychus n.sp.; Cu = Cladoceramus undulatoplicatus; Cv & Cc = Clioscaphites vermiformis-Clioscaphites choteauensis; Ss = Spinaptychus sternbergi; H = Hesperornis; D = Dolichorhynchops. Seaway curve for the Interior Seaway showing fourth-order transgression and regressions of Kauffman (1984).
Endemics: Protosphyraena pernicosa, Bananogmius zitteli, and the turtle Chelosphargis advena.
3.2
Spinaptychus n. sp. Zone
This zone is based on the distinctive aptychi of an ammonite, but the species has not yet been named. Twenty-nine taxa are known, of which two are endemic. The zone also marks the LADs for six fish species and the FAD for four fish species. Seventeen other taxa are also known in both older and younger zones. A possibly new genus of coelacanth is present that may be closely related to Macropoma (Stewart et al., 1991). This zone is upper Upper Coniacian. LAD: Belonostomus sp., Pseudocorax laevis, Ptychodus anonymous, Martinichthyes ziphoides, Protosphyraena nitida. FAD: Enchodus dirus, Protosphyraena tenuis, P. gladius, Stratodus apicalis.
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Endemics: cf. “Macropoma”, Ichthyornis cf. I. anceps.
3.3
Cladoceramus undulatoplicatus Zone
Inoceramids are one of the few invertebrates that are well preserved in the Smoky Hill Chalk. One of these, Cladoceramus undulatoplicatus, is the most distinctive and dominant in this zone (Hattin 1982). Twenty-one vertebrate taxa have been identified. However, none are endemic, and only one FAD and LAD occur. This zone marks the lowest number of vertebrate taxa in the Smoky Hill Chalk for reasons discussed below. Kauffman et al. (1993) have determined the C. undulatoplicatus zone to be upper Lower Santonian. Obradovich (1993) reports a radiometric date of 84.88 + 0.28 Ma from the top of this zone. LAD: Enchodus dirus FAD: “Pachyrhizodus” leptopsis
3.4
Clioscaphites vermiformis and Clioscaphites choteauensis Zone
Clioscaphites vermiformis and C. choteauensis are typically recognized as two separate macrofossil zones in the Western Interior (Kaufmann et al., 1993). However, because preservation of ammonites in the Smoky Chalk is so poor, Stewart (1990a) combined these two zones for convenience. The combined zone has 32 vertebrate taxa, of which four are endemic fish. The zone also marks the LAD for four fish and one reptile, and the FAD for two fish and four reptiles. The age of the zone is Middle Santonian. LAD: Paraliodesmus guadagnii, Squalicorx falcatus, Pychodus mortoni, Pteranodon sternbergi, “Pachyrhizodus” leptopsis. FAD: Kansius sternbergi, Apteodus sp., Clidastes propython, Platecarpus tympanicus, Tylosaurus proriger. Endemics: Pseudocorax falcatus, Urenchelys abditus, Caproberyx sp., Trachichthyoides sp.
3.5
Spinaptychus sternbergi Zone
This zone is based on the distinctive aptychi of an ammonite. The zone is rich in vertebrate remains, in part because of the abundance of exposures (see Bennett 2000). Thirty-one taxa of vertebrates are known in the zone. The LAD of two fish and two reptiles occur, as do the FAD of one fish and one reptile. It also has nine endemic species. This zone is Upper Santonian. LAD: Laminospondylus transversus, Kansius sternbergi, Clidastes liodontus, Tylosaurus nepaeolicus.
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FAD: “Saurodon” pygmaeus, Styxosaurus snowii. Endemics: Bananogmius evolutus, Bananogmius favirostris, Leptecodon rectus, Osmosoma garretti, Bothremys barberi, Ectenosaurus clidastoides, Pteranodon longiceps, Nyctosaurus gracilis, Parahesperornis alexi, Ichthyornis victor.
3.6
Hesperornis Zone
Williston (1897) introduced the name “Hesperornis beds” because so many of Marsh’s specimens of this flightless bird were recovered from these strata. The Hesperornis zone occupies the western-most beds of the Smoky Hill Chalk. Of the 33 vertebrate taxa, nine are endemic, including three birds. The identity of two turtles, Lophochelys natatrix and Ctenochelys stenopora, has not been established with confidence and are not included in the taxa count of Figure 1. The zone also marks the LAD for four fish and one reptile, and the FAD for one fish, two reptiles and one bird. The age for the zone is Lower Campanian. LAD: Cretoxyrhina mantelli, Apsopelix anglicus, Protosphyraena tenuis, Apteodus sp., Platecarpus planifrons. FAD: Saurocephalus lanciformis, Dolichorhynchops osborni, Hydralmosaurus serpentinus, Hesperornis regalis. Endemics: Enchodus shumardi, Squalicorax cf. aff. S. kaupi, Rhinobatus incertus, Hadrodus marshi, Protostega gigas, ?Lophochelys natatrix, ?Ctenochelys stenopora, Polycotylus latipinnis, Baptornis advenus, Apatornis celer, Ichthyornis dispar.
3.7
Dolichorhynchops Zone
Although the polycotylid plesiosaur Dolichorhynchops appears in the Smoky Hill Chalk, it is more common in the Sharon Springs Member (Carpenter 1996b). Its remains are easily diagnosed in the field making it a useful tool for identifying this zone. Twenty-six taxa are known, but it is not known which are endemic,and which mark LADs because, although vertebrate fossils are known in the overlying members of the Pierre Shale, they remain mostly unstudied. Nevertheless, based on fishes from the Bearpaw Shale (Stewart and Carpenter, in prep.), as well as the marine reptile record, a major turnover of the vertebrate fauna occurs during the five million years separating Sharon Springs “time” and Bearpaw “time.” The Dolichorhynchops zone is Middle Campanian based on its ammonite fauna. FAD: Globidens dakotensis, Plioplatecarpus cf. P. primaevus, Elasmosaurus platyurus.
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DISCUSSION
A total of 82 vertebrate taxa are known from the Smoky Hill Chalk and Sharon Springs Member (two turtle taxa whose presence is questionable are not included). This diversity includes 50 fish, 24 reptile (including dinosaurs), and 8 bird taxa. Fish therefore comprise 61% of the taxa, reptiles 29%, and birds 10%. Interestingly, the three small fishes (
