Only 1 vertebrate species was excavated from Nonconnah Creek, a tributary of the Mississippi River that flows through Memphis, Tennessee. In 1977 some kids found a skull complete with tusks and teeth of a male mastodon, later estimated to be between 15-18 years old at the time of its death. Archaeologists and geologists soon descended upon the site and conducted a wonderful study that is very exciting for the paleoecology geek in me. They found plant macrofossils and pollen, snail shells, and even insect parts in the sediment mixed with the mastodon specimen–a jackpot of information that can help scientists determined what the environment was like in this region during the late Wisconsinian Ice Age.
Nonconnah Creek is on the right side of the Mall of Memphis parking lot. The mastodon fossils were uncovered after construction workers dug drainage ditches.
Photo of tusk and teeth from the Nonconnah Creek Mastodon. This photo is from the below reference.
The mastodon found here died about 20,000 calender years ago during the Last Glacial Maximum when the Laurentide Ice Sheet reached its maximum extent as far south as central Ohio. The environment around Nonconnah Creek was much different during the LGM from that of today. A closed canopy forest consisting of spruce and oak dominated the landscape. The most common species of spruce in this forest was an extinct species known as Critchfield’s spruce (Picea critchfeldii). (See:https://markgelbart.wordpress.com/2011/09/03/the-extinction-of-critchfields-spruce-picea-critchfieldii/) This species had longer cones than the extant white spruce which it resembled. This spruce and oak forest likely extended as far south as Louisiana and as far east as western Georgia. Summers were much cooler, but winters were just slightly cooler than those of today. Average temperatures were not as cold as scientists initially thought because they were using the presence of existing species of spruce trees as a proxy for temperature range, not realizing the spruce fossils they were finding were from an extinct species that was probably at home in temperate climates. Foggy conditions often prevailed in the area then. Glacial meltwater descending down the Mississippi River struck warm fronts originating from the Gulf of Mexico creating a cool moist environment that favored spruce trees. The Mississippi River had a braided pattern with many exposed sandbars. Frequent cold winds, blowing from the northern Ice Sheets, blew sand dunes from the river into the spruce and oak forests, occasionally burying the trees. This explains how these plant fossils were preserved. (See:https://markgelbart.wordpress.com/2011/08/28/the-fossil-rich-region-of-tunica-hills-louisiana/). Other species of trees occurring in this Ice Age spruce/oak forest included willow, chestnut, black walnut, hickory, paper birch, elm, cherry, sycamore, sugar maple, and red maple. Mistletoe, a spruce tree parasite, was found here as well. Though modern hardwoods were present, they were far outnumbered by spruce.
The environment during the Farmdalian Interstadial that preceded the Last Glacial Maximum differed markedly from the spruce/oak forest discussed above. Between 32,000 BP-28,000 BP, open pine and oak woodland with prairie openings prevailed here. The Farmdalian was a weak interstadial that gradually gave way to cooler temperatures with lower evapotranspiration rates and lower CO2 levels in the atmosphere–conditions that evidentally favored spruce. Fewer thunderstorms and lightning strikes reduced the incidence of wild fire, probably also explaining why closed canopy spruce/oak became dominant over open pine and oak woodland.
Valvata tricarinata–A freshwater snail It’s a common freshwater snail of lakes presently located north of where the Laurentide Glacier extended during the Last Glacial Maximum. It’s uncommon south of that region though a disjunt relic population lives in the Savannah River, Georgia. Interestingly, this was the most common species of snail found in the Nonconnah Creek fossil site–evidence its range was displaced farther south during the Pleistocene.
Most of the Pleistocene-aged snail shells found at this site were from species commonly found in the region today, and they represent denizens of a variety of aquatic habitats from stagnant pools to fast moving streams. Dam-building beavers and natural forest debris slowed down some parts of the creek while in other parts it was unimpeded. Scientists identified 2 species of snails that no longer occur in the region. Today, Fossaria reflexa is restricted to the New England region, but during the Ice Age this species evidentally was displaced at least as far south as Tennessee. Valvata tricarinata is a common snail species today in the region that was covered by glaciers during the Ice Age. This species was also displaced south of its current range. Curiously, a few disjunct populations of Valvata are found as far south as the Savannah River, but it is not common in the southern parts of its range. However, it was the most common species of snail found at Nonconnah Creek during the Ice Age. Snails are creatures often used to illustrate slowness, but these 2 species were able to keep pace with rapid climate change when they recolonized newly available habitat after the Ice Age.
Dicaelus sculptilis, a ground beetle today found north and west of Nonconnah Creek. It was the only recognizable insect found as fossil remains, dating to the Ice Age.
Most of the grasshopper and beetle remains associated with the mastodon had been dashed to unrecognizable smithereens. However, scientists were able to identify 1 species–Dicaelus sculptilis, a ground beetle that currently ranges to the north and west of this site.
Brister, Ronals; John Armon and David Dye
“American Mastodon Remains and Late Glacial Conditions at Nonconnah Creek, Memphis, Tennessee”
Memphis State University Anthropological Research Center Occasional Papers 10 1981