Print PageIt is not clear how North America's Pleistocene megafauna became extinct. Fossil remains of this vanished community are abundant in the wetlands of Orange County NY, where they are usually found in well-stratified fine sediments rich in microfossils. This formally-glaciated region was just under the southern edge of the Wisconsinan ice sheet at last glacial maximum. As such, it frames the extinction window, thus providing an opportunity to study the timing and pattern of an extinction process that appears to have been complete by 11,000 radiocarbon years before present (14CyrBP). We report two recent finds and their paleoenvironmental context. Among a number of previously accelerator mass spectrometry (AMS) -dated specimens of the local Pleistocene fauna, these appear at the temporal boundaries of the extinction event for this region: a stag-moose (Cervalces scotti) discovered eroding from the side of a drainage ditch beside a fallow field of the Black Dirt agricultural region near Goshen NY, excavated in late 2007, and a mastodon (Mammut americanum) whose tusks were found eroding from a river bank in 2008.
Results/Conclusions
Investigation of the Cervalces site in 2008 showed three sedimentary units: a glacial gray clay, overlaid by the bone-bearing unit of peaty clay with graminoid fiber and snail shells; a fine black peat formed the uppermost unit. Samples were taken at 5cm intervals, to a depth of 260cm. Low organic accumulation characterized the glacial clay, a herb zone dominated by sedge and pine pollen. Organic carbon rose sharply in the bone bearing layer; carbonates reached 25%; spruce, pine, alder and birch were the principal pollen types indicative of the Younger Dryas climatic reversal at 11,000 14CyrBP. AMS analysis of rib fragment of the Cervalces confirmed this assessment, yielding a date of 11,040+/- 110 14CyrBP, putting it among latest known occurrences for this species.
The mastodon tusks had been left in situ since discovery during the previous fall when they eroded out of a riverbank ca.10km west of the Cervalces site. The mastodon remains were embedded in a similarly calcareous unit, also formed in shallow lake conditions; carbonates reached 28% by weight. AMS dates on tusk gave 12,350+/-45 and 12,300+/-45 14CyrBP indicating it lived as much as 1300 years earlier and may be the oldest dated mastodon in New York State.
