|Timothy H. Heaton
Department of Earth Sciences
University of South Dakota
Vermillion, SD 57069
|H. Gregory McDonald|
Hagerman Fossil Beds National Monument
P.O. Box 570
Hagerman, ID 83332
A series of quarries in the Bon Homme Gravel have yielded isolated elements of over a dozen taxa of large mammals. The most significant quarry is the Kuchta Sand Pit located 19 km west of Yankton, reported by Johnson and Milburn (1984) and Pinsof (1985, 1986). The age of this deposit is late Blancan to early Irvingtonian based on the presence of Stegomastodon mirificus, Equus cf. giganteus, Gigantocamelus spatulus, and Titanotylopus. Several new specimens have been collected from the Kuchta Sand Pit and donated to the University of South Dakota since 1986, including additional material of Equus and Hemiauchenia. Of greater significance are two new additions to the fauna, Megalonyx and Camelops.
McDonald (1977) demonstrated that Pleistocene Megalonyx comprise a single lineage that underwent a steady increase in size and can be conveniently divided into three chronospecies: M. leptostomus of the late Blancan and earliest Irvingtonian, M. wheatleyi of the later Irvingtonian, and M. jeffersonii of the Rancholabrean. The Kuchta specimen is a right third metacarpal (USDVP 1180), and its size is small when compared to the same element at other sites (Figure 1). It is most similar to M. leptostomus from the Inglis 1 A locality of the early Irvingtonian of Florida, so we refer it to that species.
There have been two previous reports of Megalonyx from South Dakota. The first is a right femur (UNSM 88438) from an isolated locality near Philip in Haakon County, first reported by Hay (1914) and illustrated by Pinsof (1986). Although no species level identification was given, it is probably M. jeffersonii based on its large size. Warren (1952) and Flint (1955) reported Megalonyx from the Bergner Gravel Pit, an Irvingtonian deposit 160 km NW of the Kuchta site. M. R. Voorhies was unable to find sloth material in the Bergner collection at the time of Pinsof's (1986) work but has since located a single second phalanx from digit four of the pes (UNSM 88506). We assign it to M. Wheatleyi based on its size and the associated taxa; the Kuchta fauna slightly predates the Bergner Pit fauna (Pinsof 1985, 1986). If these identifications are correct, South Dakota deposits have produced all three chronospecies of Megalonyx, but only one specimen of each!
The other new addition to the Kuchta fauna is Camelops sp., represented by a left I/2 (USDVP 1176), a right astragalus (USDVP 1177), and a first phalanx (USDVP 1178). These were compared with Camelops from Natural Trap Cave (KU) and the Bergner Gravel Pit (SDSM 5181) and found to be identical. The proximal phalanx is particularly distinct because the suspensory ligament scar extends so far distally on the shaft, a character noted and illustrated by Breyer (1974) and Voorhies and Corner (1986). The phalanx measures at the upper end of the size distribution for Camelops with a maximum length of 126.5 mm and a proximal transverse width of 50.4 mm. The astragalus has a lateral length of 83.5 mm and a minimum length of 65.3 mm, making it large compared with Nebraska Camelops (Breyer 1974) but typical of those from Rancho La Brea (Webb 1965).
Green (1977) reported an upper canine of Camelops (SDSM 7522) from another quarry of similar age in Yankton County, and Camelops is known from deposits as early as middle Blancan in Nebraska (Barbour and Schultz 1937, Voorhies and Corner 1986), so its presence in the Kuchta Sand Pit is no surprise.
We extend thanks to Robert L. Kuchta for collecting fossils from his quarry and donating them to the University of South Dakota. We also thank Gary D. Johnson of the University of South Dakota (USDVP), Philip R. Bjork and Janet L. Whitmore of the South Dakota School of Mines and Technology (SDSM), Michael R. Voorhies and R. George Corner of the University of Nebraska State Museum (UNSM), Larry D. Martin of the University of Kansas (KU), and John D. Pinsof of Daemen College for access to fossils in their care and for helpful discussions concerning this project.
Breyer, J. 1974 Examination of Selected Postcranial Elements in Pleistocene Camelids. Contributions to Geology 13:75-85.
Flint, R. F. 1955 Pleistocene Geology of Eastern South Dakota. U.S. Geological Survey Professional Paper 262:1-173.
Green, M. 1977 Dipoides (Rodentia: Castoridae) from Yankton County, South Dakota. Journal of Paleontology 51:136-138.
Hay, O. P. 1914 The Pleistocene Mammals of Iowa. Annual Report, Iowa Geological Survey 23:1-662.
Johnson, G. D., and S. E. Milburn 1984 Pathological Evidence of an Injured Equid, and Associated Fossils of Late Blancan(?) Age from the Bon Homme Gravel, Yankton County, South Dakota. Proceedings of the South Dakota Academy of Sciences 63:77-84.
Kurtén, B., and E. Anderson 1980 Pleistocene Mammals of North America. Columbia University Press.
McDonald, H. G. 1977 Description of the osteology of the extinct gravigrade edentate, Megalonyx, with observations on its ontogeny, phylogeny and functional anatomy. Unpublished M.A. thesis, University of Florida, Gainesville.
Pinsof, J. D. 1985 The Pleistocene Vertebrate Localities of South Dakota. Dakoterra 2:233-264.
Pinsof, J. D. 1986 The Pleistocene Vertebrate Fauna of South Dakota. Unpublished M.S. thesis, South Dakota School of Mines and Technology, Rapid City.
Voorhies, M. R., and R. G. Corner 1986 Megatylopus(?) cochrani (Mammalia: Camelidae): a Re-evaluation. Journal of Vertebrate Paleontology 6:65-75.
Warren, C. R. 1952 Probable Illinoian Age of Part of the Missouri River, South Dakota. Geological Society of America Bulletin 63:1143-1155.
Webb, S. D. 1965 The Osteology of Camelops. Bulletin of the Los Angeles County Museum 1:1-54.