Paleocommunity of Late Pleistocene Megafauna Found Along the Lower Mississippi Delta. Gravel Bars. Christine Beck, Danielle Husley, Nina L. Baghai-Riding, ...
Paleocommunity of Late Pleistocene Megafauna Found Along the Lower Mississippi Delta Gravel Bars Christine Beck, Danielle Husley, Nina L. Baghai-Riding, and Eric Blackwell
Introduction 15%
Mississippi is usually not regarded as a place to find large quantities of vertebrate fossils compared with other regions of the United States. In fact, this area is usually neglected and is often regarded as both an ‘agricultural bread belt’ in reference to the vast amounts of crop plants produced in the area, and the birthplace of blues music. However, numerous remains of megafauna are exposed along gravel bars when the water level of the Mississippi River is low. Individuals can travel by boats to venture, explore, and collect specimens from these gravel bars. For example, one collection referred to as the Looper collection, contains specimens collected over a six-year span (1989-1995). This collection consists of 550 specimens including cranial, teeth, and disarticulated post-cranial elements. These specimens were collected from nineteen gravel bars that extend from East Carroll Parish in Louisiana into Bolivar, Washington, and Issaquena Counties in Mississippi and Chicot, Desha, and Phillips Counties in Arkansas (Figure 1).
45%
40%
Table of organisms associated with the Looper collection.
Fig 2. Digestive anatomy of ice age mammals associated with the Looper collection. Peccary was counted twice because it was both hind gut and foregut.
Looper Collection/Vertebrate Fauna The Looper Collection, is significant in that it possesses 19 assorted large megafauna mammals (Table 1) and is considered to date to the Rancholabrean, based on the presence of Bison (bison), Mammut americanum Kerr (American mastodon), Mammuthus primigenius Blumenbach (mammoth), Arctodus simus Cope (short-faced bear; Figure 3C), and Tapirus haysii Leidy (giant tapir). Other Rancholabrean associated faunas include perissodactyls such as Equus complicates Leidy (extinct horse; Figure 3E), carnivores such as Canis dirus Leidy (dire wolf ), artiodactyls like Paleolama mirifica Simpson (stout-legged llama), Megaloynx jeffersonii Harlan (giant ground sloth; Figure 3H) and Cervalces scotti Ledekker (stag moose), large rodents such as Castoroides ohioensis Foster (giant ice age beaver; Figure 3F), as well as other taxa (Figure 3). Several taxa in this assemblage have not been previously reported from the northern Mississippi Delta Coastal Plain or high latitude Mississippi Delta (Bolivar and Coahoma) regions: Bootherium bombifron (Harlan) (woodland musk ox), Cervalces scotti (Figure 3B), Paleolama mirifica, Tapirus haysii, Platygonus compressus LeConte (flat-headed peccary; Figure 3G), Equus complicatus, and Trichechus manatus L. (American manatee). In addition, the John Connaway collection, donated to the Pink Palace Museum in Memphis consists of 2288 vertebrate elements from local Mississippi gravel bars in the Mississippi Delta; 24 taxa of large mammals including horn cores of Bison bison antiquus, the Nothrotheriops (small western ground sloth), and a jaw of Panthera leaatrox (American lion) (Dockery and Thompson, 2016).
B. A.
30 cm
56 cm
Fig.1- Late Pleistocene fossil sites associated with the Looper collection
Ancient Bison Bootherium bombifron
C.
White Tailed Deer Odocoileus virginianus D.
Great Short- Faced Bear Arctodus simus
15 cm
Environmental/Geological Setting The Mississippi River consisted of braided channel belts throughout the central lower Mississippi valley during the Rancholabrean. For example, the Kenneth (16.1 – 14.4 ka) and Morehouse (12.4 – 11.3 ka) braid belts existed along the northern Eastern Lowlands east of Crowley’s Ridge and extended into the Yazoo Basin of Mississippi (Rittenour, at al. 2007). These sediments were derived from glacial outwash from the Ohio, Mississippi, and Missouri Rivers (Rittenour et al. 2007; Saucier, 1974). Great meltwater flows occurred down the Mississippi river and into the Gulf of Mexico between 12.7 ka to 12.100 ka; this abundance of freshwater may have lowered salinity in the Atlantic Ocean based on the abundance of reworked calcareous nannofossils in the Orca Basin, approximately 180 miles southwest of the Mississippi Delta (Dockery and Thompson, 2016). Sea-level was 60 meters (197 ft.) below present level (Dockery and Thompson, 2016). The Mississippi River switched to a meandering regime after 11.3 ka (Dockery and Thompson, 2016). This change is attributed to the breach at Thebes Gap at Crowley’s Ridge approximately 10 ka when Lake Agassiz overflowed its dam, flooding the Mississippi Basin (Dockery and Thompson, 2016; Rittenour et al. 2007; Figure 4). From 12,800 to 11,200 BP, climatic conditions became drier and pine briefly increased before oak became dominant (Watts and Hansen, 1995). Habitats were open and included a high percentage of shrub land and prairie vegetation (Watts, 1980; Figure 5). Drying climatic conditions would force large herbivores to cluster around water holes which caused overcrowding, increased nutritional stress, and vulnerability to Paleoindian hunters (Haynes, 1991). Mastodons, mammoths, bison and equids also were known to migrate long distances based on 87Sr/86Sr ratios from Rancholabrean sites in Florida (Hoppe and Koch, 2007). The Looper assemblage possesses almost an equal number of hindgut and foregut taxa (Figure 2). Erosional margins around the Mississippi river braided channels and bordering floodplains probably caused the spread of grasses which may have attributed to the abundance of grazing animals including mammoths, horses, and bison. Numerous freshwater lakes also probably served as an important resource for large herbivores. Tapirs and llamas probably lived along riverbanks as well. Browsing animals, including mastodons and giant ground sloths, probably ate plants associated with forests that bordered the grasslands. Dire wolves, saber-toothed cats, short-faced bear, black bear, and lions common to North America at that time were able to sustain themselves based on the large numbers of herbivores that were found in this area (Figure 2). The low salinity of the Atlantic Ocean and the receding of the glaciers might have also been responsible for the migration of the manatee up the Mississippi River (Figure 3D).
Fig 4. Limit of the Wisconsin glaciation showing Lake Agassiz (Seeb et al., 1987). Manatee Trichechus manatus 38 cm
E.
F. 10 cm
Modern Beaver Castor canadensi
15 cm
Giant Ice Age Beaver Castoroides ohioensis
Fossil Horse Equus complicatus
G.
H. 15 cm
Fig 5. Preliminary vegation zone map of North America circa 13 ka. (https://markgelbart.wordpress.com/2013/0/page/2/).
Gaint Ground Sloth Megalonyx jeffersonii
References Dockery, T., and D.E. Thompson. 2016. The Geology of Mississippi. University Press of Mississippi, Jackson. 751 pp.
Acknowledgments
Haynes, G. 1991. Mammoths, mastodonts, and elephants: Biology behavior, and the Fossil Record, Cambridge University Press, New York. Hoppe, K. A. and Koch, P. L. 2007. Reconstructing the migration patterns of late Pleistocene mammals from northern Florida, USA, Quaternary Research 68:347-352.
We thank Mr. Lonney Looper for photographs and donation of his vertebrate ice age collection to Delta State University. We would also like to show our gratitude to Dr. Don Spalinger at the University of Alaska in Anchorage, Alaska for his wisdom about hindgut and foregut mammalian herbivores. This presentation was partially supported by a NASA Space Grant and the Delta State University Student Government Association and Department of Biological Sciences.
Rittenour, T. M., M. D. Blum, and R. J. Goble. 2007. Fluvial evolution of the lower Mississippi River valley during the last 100 k.y. glacial cycle: Response to glaciation and sea-level change. Geologic Society of America Bulletin 119(5/6):586-608. Saucier, R. T., 1974, Quaternary Geology of the Lower Mississippi Valley, Arkansas Archeological Survey Research Series No. 6. Second Printing,1984. 26 pgs. Watts, W. A. 1980. The late Quaternary vegetation history of the southeastern United States. Annual Review of Ecology and Systematics 11:387-409.
Long nosed peccary Mylohyus nasatus
Fig 3. Assorted bone, jaws. and teeth specimens obtained from the Mississippi Delta gravel bars.
20 cm
