Passport-In-Time Microvertebrate Fossil Project at the University of Wyoming Geological Museum: Late Cretaceous Paleontological Resources in the Public Eye
Thunder Basin National Grasslands, Wyoming, 1999
by Brent H. Breithaupt, Geological Museum, University of Wyoming, Laramie, WY 82071
Abstract—During two weeks in February of 1999, the University of Wyoming Geological Museum conducted a laboratory project working with Late Cretaceous microvertebrate fossils collected from the Lance Formation of the Thunder Basin National Grassland in northeastern Wyoming. This project utilized volunteers under the auspices of the Forest Service's Passport-in-Time (PIT) program. The program at the University of Wyoming was one of the first PIT programs dealing with paleontology on Forest Service lands. The Forest Service and UW Geological Museum established this project to help one another accomplish mutually beneficial objectives related to proper management of paleontological resources on lands administered by the Forest Service. One such objective was to get the public involved with paleontology through participation in scientific research, in hopes of increasing their understanding of the management of fossil resources on federal lands. Lance Formation microvertebrate fossils represent important components of the latest Mesozoic vertebrate faunas of the Western Interior. Two previously unstudied sites were the focus of this project. The participants recognized two very different faunas through screen-washing, sorting, and fossil identification. These Late Cretaceous fossils from the Thunder Basin National Grassland of Wyoming are examples of the paleontological resources that are being studied through the collaborations of scientists, students, volunteers, and land managers. As the public becomes more involved in the scientific process, they gain a better understanding of fossil resources and the importance of studying them. Through programs like PIT, people with different backgrounds are encouraged to become partners in paleontological resource management.
Perhaps now more than ever before, the general public travels to museums to learn about the intriguing beasts of the past and the exciting wonders of our ancient world. They marvel at how our planet has evolved through its 4.5 billion year history and how animals and plants have changed through time. One advantage of the current popularity of dinosaurs is that more people are thinking about paleontology; how it works and how much there is still left to learn. Museums provide an important link between scientists and the public, by translating the information provided by researchers into interesting stories about our past.
In addition to telling the stories of past life, most museums are mandated to protect and preserve the scientific resources in their collections. In addition, museums are entrusted with the responsibility to ensure the protection of these resources, by educating the public about their importance. This means not only discussing current scientific ideas, but also demonstrating the need for protecting this material from activities that could be detrimental to the progress of science. This exchange of information often translates into museum exhibits. Vertebrate fossils are excellent examples of geological resources in need of protection, because of their rarity and unique educational and scientific values. While the "megafauna" is often the focus of public attention, the often overlooked microvertebrate fossils are critical to our understand of ancient ecosystems.
During February 14-19 and 21-26, 1999, the University of Wyoming Geological Museum (with Forest Service participation) conducted an in-house laboratory project working with Late Cretaceous microvertebrate fossils collected from the Lance Formation of the Thunder Basin National Grassland in northeastern Wyoming. This project utilized volunteers under the auspices of the Forest Service's Passport-In-Time program. There were 20 available openings for participants. Those 18 and over were invited to the program, but younger participants were encouraged to attend with a responsible adult. No special skills were required other than an interest in lab work and the ability to look through a microscope for extended periods of time. To facilitate the understanding and participation of the volunteers in the process of microvertebrate analysis of Wyoming's Cretaceous inhabitants, the project focused on laboratory research and activities, including the screen-washing, sorting, and identifying of fossils. The Late Cretaceous Lance Formation microvertebrate fossils represent the little animals that scurried beneath the feet of the late Mesozoic giants.
The Forest Service and Geological Museum established this project to help one another accomplish mutually beneficial objectives related to the proper management of paleontological resources on Forest Service lands. One such objective was to get the public involved with paleontological research (such as microvertebrate faunal analysis), in hopes of increasing their understanding of the management of fossil resources on federal lands. This project utilized cientifically important fossil-rich samples from Forest Service managed land. The research being conducted is an excellent example of the proper management, utilization, and study of the fossil remains. Furthermore, the public was involved in the scientific process. As a consequence, by becoming partners in paleontological resource management, they acquired a better understanding of the scientific significance of these resources.
In addition, the project's focus on microvertebrate fossils furthers the scientific understanding and management of Lance Formation fossil deposits. Future studies of this material will include the comparison of ancient and modern environments, and will provide additional information for the management of publicly held fossil deposits. This will benefit the Forest Service and is also part of the Geological Museum's mission. As a result, the Forest Service gained valuable information about fossil resources and provided public participation related to the fossils in the Thunder Basin National Grassland.
THUNDER BASIN NATIONAL GRASSLAND
The Thunder Basin National Grassland is managed by the USDA Forest Service as part of the Medicine Bow National Forest. The Thunder Basin National Grassland occupies more than 572,000 acres in a mosaic of state, federal, and private lands totaling over 1.8 million acres. The resources of the Thunder Basin National Grassland, like the National Forests, are managed for a variety of interests and uses. The Forest Service uses the concept of Multiple Use management. The blending of multiple use objectives in a way that conserves and protects the land, while at the same time allowing for the use of its resources, are the basic principles of Multiple Use Management. Currently, livestock grazing, wildlife habitat, mineral production, and recreation are the major uses of these lands. The Grassland, like so many other federal lands, preserves the rich paleontological heritage and fossil diversity of our country, and thus, is a natural national repository of fossil remains.
Passport-In-Time (PIT) is a volunteer program of the Forest Service. PIT provides opportunities for individuals and families to work with professional archaeologists, historians, and paleontologists on various research projects. PIT volunteers take part in research on national forests across the nation. Their participation in the PIT program helps in the understanding of the historic and prehistoric stories of North America, as well as assisting in the preservation of the fragile sites that chronicle these stories. PIT participants share in new discoveries, learn about science and research, and meet many new friends. The PIT program provides an important opportunity for the public to contribute to natural heritage resource protection and management. The Passport-In-Time Microvertebrate Fossil Project at the University of Wyoming was one of the first PIT programs to utilize paleontological resources on Forest Service lands.
As Forest Service lands may contain important paleontological resources, paleontology partnerships are an important management tool for the protection of these resources. Fossils on public lands can help document the rich history and diversity of life on our planet. The Forest Service's responsibility for the management and protection of public lands, includes stewardship of its scientific resources. To better protect and manage paleontological resources for present and future generations, the Forest Service works closely with paleontologists at museums and universities to discover, document, and interpret the fossils found on public lands. The fossils in the Thunder Basin National Grassland of Wyoming are examples of the paleontological resources that are being studied through the collaborations of scientists, students, volunteers, and land managers.
The most prolific unit in Wyoming for Late Cretaceous vertebrate fossils is the Lance Formation (Breithaupt, 1997). It is dominated by nonmarine, coastal floodplain sandstones, mudstones, and marls, with marginal marine sandstones and shales in its lower parts. The latest Cretaceous depositional environment in Wyoming was a warm temperate to subtropical, seasonal floodplain on the west coast of an eastward-regressing inland seaway. The Lance Formation encompasses a fairly short period of geologic time (approximately 1.5 million years) at the end of the Maastrichtian. It reaches over 750 meters in thickness and is found throughout Wyoming. Because of the mammalian fauna found in the Lance Formation, the fossils from this unit are assigned to the Lancian "age" (Russell, 1975; Lillegraven and McKenna, 1986).
The Lance Formation contains one of the best-known Late Cretaceous vertebrate faunas (Archibald, 1996; Estes, 1964; Clemens, 1960, 1963, 1966, 1973; Derstler, 1994; Breithaupt, 1982, 1985; Whitmore, 1985; Whitmore and Martin, 1986; Webb, 1998, 2001). The diverse fauna contains various cartilaginous and bony fishes, frogs, salamanders, champsosaurs, turtles, lizards, snakes, crocodiles, pterosaurs, mammals, birds, and some of the best known Cretaceous dinosaurs (e.g.,Triceratops, Torosaurus, Tyrannosaurus, Edmontosaurus, Pachycephalosaurus, Ankylosaurus, Edmontonia, Thescelosaurus, Troodon, Dromaeosaurus, and Ornithomimus). Derstler (1994) calculated that 85% of the Lance Formation dinosaurs were represented by the ceratopsian Triceratops, with another 12% of the dinosaur fauna represented by the hadrosaur Edmontosaurus. Abundant remains of small vertebrates (e.g., mammals, lizards, and snakes) and ceratopsian dinosaurs were collected for O. C. Marsh by J. B. Hatcher during the years 1889-1894 (Hatcher, 1893; Hatcher et al., 1907). Clemens (1963) provides an excellent summary of investigations done in the Lance Formation of eastern Wyoming.
The physical environment and biotic diversity of the Late Cretaceous of Wyoming is comparable to that seen in the southern United States today. Russell (1989) provides a vivid description of Lancian paleoecology. The subtropical Gulf Coast of the United States is perhaps the best modern correlative to Wyoming's latest Cretaceous landscape. The Gulf Coast has a diverse biota, with a distinctive assemblage consisting of alligators, crocodiles, soft-shelled turtles, sirens, gars, and bowfins, similar to that found in the latest Cretaceous fossil record. The lush lowland vegetation, meandering streams with coastal connections, and areas of occasional ponding with seasonal water restrictions relate closely to the floodplain environments associated with the western epicontinental sea during latest Cretaceous time (Breithaupt, 1982). Knowlton (1922) and Dorf (1942) provide descriptions of the flora of the Lance Formation.
Named for a small drainage (Lance Creek) in the eastern part of Wyoming, the Lance Formation is best known for the exposures found in that region of the Powder River Basin. However, the 1872 discovery of a partial skeleton of a dinosaur from the western part of the state by Drs. F.B. Meek and H.M. Bannister (while working for F.V. Hayden's Geological Survey of the Territories) was the first indication of the paleontological importance of this unit (Breithaupt, 1982; 1994). E.D. Cope (1872) collected and described the material and named a new species of dinosaur, Agathaumas sylvestris. Currently, Agathaumas is thought to be a form of Triceratops (the most common horned dinosaur found in Wyoming and Wyoming's State Dinosaur). Marsh (1889) defined the genus Triceratops on material he had originally called Ceratops horridus from the Lance Formation of Niobrara County, Wyoming. The type area of the Lance Formation in east-central Wyoming has produced hundreds of Triceratops fossils, including at least 100 skulls Derstler, 1994).
Since the discovery of Agathaumas, literally tens of thousands of Late Cretaceous vertebrate remains have been recovered from the Lance Formation. Fossil vertebrate material ranging from important microscopic elements to extensive bonebeds, with nearly complete, sometimes articulated dinosaur skeletons, are known. Some of these monospecific bonebeds may contain over 10 bones per square meter (Derstler, 1994). Spectacular specimens like the dinosaur "mummies" (hadrosaur skeletons surrounded by skin impressions) have also been found in the Lance Formation (Lull and Wright, 1942). Carpenter (1982) reported baby dinosaur fossils from this unit from microvertebrate sites. Lockley (personal communication) is studying a fairly diverse tracksite in the Lance Formation.
In addition, the first discoveries of Tyrannosaurus rex can be traced to the Lance Formation. In 1892, following one of Hayden's routes into South Dakota, Cope (1892) discovered some vertebral fragments that he named Manospondylus gigas.Famed dinosaur hunter Barnum Brown, while exploring the same area of South Dakota and eastern Wyoming, discovered a partial skeleton in 1900. H. F. Osborn (1905) named this specimen Dynamosaurus imperiosus ("powerful imperial lizard"). However, earlier in the same paper Osborn also named a second and more complete skeleton of this dinosaur from Montana, Tyrannosaurus rex ("king of the tyrant lizards").
During the summer of 1994, an archeological survey was conducted for the Forest Service in the Thunder Basin National Grassland in eastern Wyoming. During the course of this inventory, some pieces of fossil bone were discovered in sandstones of the Lance Formation in Weston County. The University of Wyoming (UW) Geological Museum and South Dakota School of Mines and Technology (SDSM) Museum of Geology were contacted. Upon closer inspection, the bones were identified as pieces of the bony plates from an armored dinosaur. The following summer, a crew from the SDSM Museum of Geology returned to the site (SDSM V9523) with the hopes of finding more bones. The summer field program involved a crew made up of students, professors, and members of the general public. The rocks and fossils at the site were thoroughly documented with photos and written notations. Meter grid squares were laid out at the site and were carefully troweled in search of fossil bone. Fortunately, many parts of this dinosaur were recovered, resulting in the first associated partial skeleton of a nodosaurid ankylosaur from eastern Wyoming. Once collected, the specimen was brought to the lab at the SDSM Museum of Geology in Rapid City, where it was prepared, studied, and cataloged (SDSM 34468) by students. Close examination indicated that the specimen represented the armored dinosaur Edmontonia (Finlayson, 1997). Several microvertebrate (e.g., multituberculate mammal, garfish, crocodile, turtle, and dinosaur) remains were found near the Edmontonia specimen. These were discovered while crawling the weathered sandstone outcrops in search of more bones during a June snowstorm. Additional surveys resulted in several areas of promising exposures from which samples were collected for screen-washing (see Martin and Finlayson, 1997). The screen-wash material was taken to the South Dakota School of Mines and Technology and awaited processing. In 1999, material from two of these sites (i.e., SDSM V9717 - Hoodoo Point Site and SDSM V9718 - Gunsight Ledge Site) was transferred to the UW Geological Museum for use during the Passport-In-Time Microvertebrate Fossil Project. PIT participants took part in standard microvertebrate wet screening washing techniques (Hibbard, 1949; McKenna, 1962; McKenna et al., 1994). Historically, Barnum Brown (1906) was one the first investigators to systematically screen-wash Cretaceous units for microvertebrate fossils.
The indoor screen-washing facility at UW was used to wash the material from the two sites. Samples were placed in screened wash boxes and gently agitated. After the very fine material was washed though the brass screens, the boxes were set outside to dry. Once dried, the Thunder Basin material was concentrated into coffee cans and brought into the museum, where eager PIT volunteers waited to pick through the concentrate. Each PIT participant was provided with his/her own binocular microscope, sorting tools, and microvertebrate identification guide.
While the Thunder Basin Lance Formation material was being washed and dried, PIT participants learned how to sort and identify microvertebrate material from a well-studied Cretaceous site (UW Locality V-81013; Hewitt's Foresight). Worked by individuals from the University of Wyoming for nearly a decade (Breithaupt, 1985; Webb, 1998; 2001), this Lance Formation site from Park County in the northeastern part of Wyoming, is known to contain a tremendously diverse fauna of microvertebrates. Several important mammal specimens were found by the PIT participants for Webb's dissertation.
The Hoodoo Point locality washed best (as it was a weathered, fine-grained mudstone) and the concentrate was relatively easy to microscopically sort. Material from the Gunsight Ledge locality was coarser grained and did not wash as well. As a result, the microscopic sorting of this material was more tedious and provided less frequent results. PIT participants were expected to pick-out all identifiable bones and teeth and categorize the material to the best of their ability. As the project was held within the exhibit hall of the museum, PIT participants became impromptu docents and were quite willing to explain microvertebrate research to regular museum visitors.
The following is the list of fossils discovered by participants in the 1999 Passport-in-Time Microvertebrate Fossil Project at the UW Geological Museum. The number of specimens assigned to each taxon is also listed. Those specimens not identifiable to a particular taxon were not listed.
GUNSIGHT LEDGE (SDSM V9718) MICROVERTEBRATE FAUNA:
Myledaphus sp. (6 specimens)
Atractosteus sp. (45 specimens)
Unidentified genus and species (33 specimens)
Genus and species understudy (6 specimens)
HOODOO POINT (SDSM V9717) MICROVERTEBRATE FAUNA:
Lonchidion sp. (4 specimens)
Squatirhina sp. (3 specimens)
Myledaphus sp. (51 specimens)
Acipenser sp. (7 specimens)
Amia sp. (6 specimens)
Atractosteus sp. (3 specimens)
Platacodon sp. (1 specimen)
Scotiophyrne sp. (3 specimens)
Scapherpeton sp. (3 specimens)
Prodesmodon sp. (2 specimens)
Habrosaurus sp. (2 specimens)
Genus and species understudy (9 specimens)
Leidyosuchus sp. (1 specimen)
Dromaeosaurus sp. (1 specimen)
Paronychodon sp. (1 specimen)
Thescelosaurus sp. (2 specimens)
Edmontosaurus sp. (1 specimen)
Triceratops sp. (45 specimens)
Alphadon sp. (2 specimens)
The Hoodoo Point Site contains a fairly diverse fauna (e.g., bony and cartilaginous fishes, frogs, salamanders, lizards, crocodiles, dinosaurs, and mammals). Many very delicate bones were preserved and subsequently recovered during screen-washing. Material from this site is comparable with that from other Late Cretaceous sites in the Western Interior (Breithaupt, 1982). The taphonomic scenario for the diversity of taxa and preservation of the material are interesting aspects of the Hoodoo Point Site still under investigation. Further collecting at the locality for additional microvertebrates is recommended. The Gunsight Ledge Site has a less diverse fauna, but contains an interesting accumulation of lizard and garfish material. Continued study of this site should prove interesting. The lizard material from both sites is under study.
The specimens from these two sites will be cataloged into the collections at the Museum of Geology, South Dakota School of Mines and Technology (SDSM 47705-48004). As the UW Geological Museum is currently engaged in a number of research projects dealing with latest Cretaceous sites in Wyoming, the material from the Thunder Basin National Grassland will be incorporated into the comparative analyses of lower vertebrate faunas around the State. In addition, the successful public outreach components of this project have been presented to scientists and resource managers in the region.
SUMMARY AND CONCLUSIONS
Since 1872, when the first dinosaur was discovered in western Wyoming, Mesozoic vertebrate fossils have been found throughout the State. Although the biggest boom for Mesozoic paleontology in Wyoming was in the late 1880s, when scientists from the East were collecting for their institutions, paleontologists continue to make important discoveries in Wyoming today. Many of the same collecting practices that were used by paleontologists over 100 years ago are still in practice. Today, fossils from Wyoming's Lance Formation are highlighted in exhibits and research collections in museums throughout the world. Fossil remains range from isolated fragments to complete skeletons.
The paleoecology of the Late Cretaceous of Wyoming is fairly well understood, as a result of over 100 years of study. However, even after more than a century of work, important vertebrate paleontological discoveries are still being made from the Lance Formation in Wyoming. As the potential for new discoveries in the Rocky Mountain West is high, interagency cooperation (to share expertise and resources) is essential to collect, study, interpret, exhibit, and preserve these specimens for future generations. The Passport-In-Time Microvertebrate Fossil Project exemplifies how paleontological resources can be studied through the collaborations of scientists, students, volunteers, and land managers. The program highlights the opportunities for multiple uses of paleontological resources, emphasizing their scientific, educational, interpretive, and recreational values of the fossil record in the documentation of the history of life on earth, which provides a lasting legacy for future generations.
Appreciation is extended to all of the PIT participants who made this project so enjoyable. Thanks to Michael Webb for his help and presentations during the two weeks in February. Gratitude goes out to Thomas Adams for the illustrations used in this report. Michael and Thomas were also both very helpful in the identifying and cataloging of the fossil material. Veronica Sanchez was instrumental in arranging the PIT participants housing on campus. Special thanks go to Forest Service representatives Ian Ritchie, Joe Reddick, Barbara Beasley, and Rusty Dersch for their help in arranging and participating in this project. Beth Southwell and Neffra Matthews provided valuable comments on the manuscript. Various anonymous reviewers also provided valuable suggestions on this manuscript. Finally, thanks goes out to the Forest Service for assistance in funding this program.
Archibald, J. D., 1996. Dinosaur extinction and the end of an era: Columbia University Press, New York, 237 p.
Breithaupt, B.H., 1982. Paleontology and paleoecology of the Lance Formation (Maastrichtian), east flank of Rock Springs Uplift, Sweetwater County, Wyoming. Contributions to Geology, v. 21, p. 123-151.
________, 1985. Nonmammalian vertebrate faunas from the Late Cretaceous of Wyoming, in Nelson, G. E. (ed.), hirty-sixth Annual Field Conference Guidebook, Wyoming Geological Association, Casper, p. 159-175.
________, 1994. The first dinosaur discovered in Wyoming, in Nelson, G. E. (ed.), Forty-fourth Annual Field onference Guidebook, Wyoming Geological Association, Casper, p. 15-23.
_______, 1997. Lance Formation, in Currie, P. J and Padian K. (eds.), Encyclopedia of dinosaurs, Academic Press, San Diego, p. 394-395.
Brown, B., 1906. Report of expeditions of 1906 to the Montana Laramie, in 1906 Annual Report of the Department of Vertebrate Paleontology, American Museum of Natural History.
Carpenter, K., 1982. Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod, Contributions to Geology, v. 20, no. 2, p. 123-134.
Clemens, W.A., 1960. Stratigraphy of the type Lance Formation, Report of the XXI International Geological Congress (Norden), Part V (Proceedings of Section 3 - The Cretaceous-Tertiary Boundary), p. 7-13.
________, 1963. Fossil mammals of the type Lance Formation, Wyoming. Part I. Introduction and Multituberculata. University of California Publications in Geological Sciences, v. 48, p. 1-105.
________, 1966. Fossil mammals of the type Lance Formation, Wyoming. Part II. Marsupialia. University of California Publications in Geological Sciences, v. 62, p. 1-122.
________, 1973. Fossil mammals of the type Lance Formation, Wyoming. Part III. Eutheria and summary. University of California Publications in Geological Sciences, v. 94, p. 1-102.
Cope, E.D., 1872. On the existence of Dinosauria in the Transition Beds of Wyoming. Proceedings of the American Philosophical Society, v. 12, p. 481-483.
_______, 1892. Fourth note on the Dinosauria of the Laramie. American Naturalist, v. 26, p. 756-758.
Derstler, K., 1994. Dinosaurs of the Lance Formation in eastern Wyoming, in Nelson, G. E. (ed.), Forty-fourth Annual Field Conference Guidebook, Wyoming Geological Association, Casper, p. 127-146.
Dorf, E., 1942. Upper Cretaceous Floras of the Rocky Mountain Region, II, Flora of the Lance Formation at its type locality, Niobrara County, Wyoming: Carnegie Institute of Washington, Publication 508, Contributions to Paleontology, p. 81-168.
Estes, R., 1964. Fossil vertebrates from the Late Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences, v. 49, p. 1-180.
Finlayson, H.C., 1997. The most complete armored dinosaur (Nodosauridae) from the Late Cretaceous (Maastrichtian) Lance Formation of eastern Wyoming (M.S. Thesis): Rapid City, South Dakota, South Dakota School of Mines and Technology 86 p.
Hatcher, J.B., 1893. The Ceratops beds of Converse County, Wyoming, American Journal of Science, series 3, no. 45, p. 135-144.
_______, 1896. Some localities for Laramie mammals and horned dinosaurs, American Naturalist, February 1, p. 112-120.
Hatcher, J.B., O.C. Marsh, and R.S. Lull, 1907. The Ceratopsia: United States Geological Survey Monograph 49, United States Government Printing Office, Washington, 300 p.
Hibbard, C.W., 1949. Techniques of collecting microvertebrate fossils. Contributions of the Museum of Paleontology, University of Michigan, v. 3, no. 2, p. 7-19.
Knowlton, F.H., 1922. The Laramie Flora of the Denver Basin. United States Geological Survey Professional Paper 130, United States Government Printing Office, Washington, 175 p.
Lillegraven, J.A. and M.C. McKenna, 1986. Fossil mammals from the "Mesaverde" Formation (Late Cretaceous, Judithian) of the Bighorn and Wind River basins, Wyoming, with definitions of Late Cretaceous North American land-mammal "ages." American Museum Novitates, no. 2840, p. 1-68.
Lull, R.S. and N.E. Wright, 1942. Hadrosaurian dinosaurs of North America. Geological Society of America Special Paper 40, p. 1-242.
Marsh, O.C. 1889. Notice of gigantic horned Dinosauria from the Cretaceous. American Journal of Science, v. 38, p. 173-175.
Martin, J.E. and H.C. Finlayson, 1997. 1997 paleontological survey of a portion of the Thunder Basin National Grassland, eastern Wyoming: A report to the Medicine Bow National Forest.
McKenna, M.C., 1962. Collecting small fossils by washing and screening, Curator, v. 5, no. 3, p. 221-235.
McKenna, M.C., A.R. Bleefeld, and J.S. Mellett, 1994, Microvertebrate collecting: Large-scale wet sieving for fossil microvertebrates in the field, in Leiggi, P. and May, P. (eds.), Vertebrate paleontological techniques: Volume 1, Cambridge University Press, New York, p. 93-111.
Osborn, H.F., 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs. American Museum of History Bulletin, v. 21, p. 259-265.
Russell, D.A, 1975. Mammalian faunal succession in the Cretaceous System of western North America. in The Cretaceous System in the Western Interior of North America, Geological Association of Canada, Special Paper, no. 13, p. 137-161.
Russell, D.A.,1989. An odyssey in time: the dinosaurs of North America, University of Toronto Press, Toronto, 239 p.
Webb, M.W., 1998. A revised summary of Lancian (Latest Cretaceous) mammal localities with introduction to a new Lancian locality (Lance Formation) in the southwestern Bighorn Basin, in Keefer, W.R. and Goolsby, J.E. (eds.), Thirty-sixth Annual Field Conference Guidebook, Wyoming Geological Association, Casper, p. 131-136.
_______, 2001. Fluvial architecture and Late Cretaceous mammals of the Lance Formation, southwestern Bighorn Basin, Wyoming, The University of Wyoming, Doctoral Dissertation.
Whitmore, J.L., 1985. Fossil mammals from two sites in the Late Cretaceous Lance Formation in northern Niobrara County, Wyoming, in Martin, J. E. (ed.), Fossiliferous Cenozoic deposits of western South Dakota and northwestern Nebraska: Dakoterra, v. 2, p. 353-367.
Whitmore, J.L. and Martin, J.E., 1986. Vertebrate fossils from the Greasewood Creek locality in the Late Cretaceous Lance Formation of Niobrara County, Wyoming: Proceedings of the South Dakota Academy of Science, v. 65, p. 33-50.