GEOLOGIC AGE AND ISOTOPIC ANALYSIS OF A YOUNG MASTODON FROM NORTHWEST OHIO

The cause of the megafaunal mass extinctions at the end of the Pleistocene is still debated. One victim of this extinction event is the American mastodon (Mammut americanum), a proboscidean widespread in North America. Identifying mastodon individuals that died close to the Pleistocene-Holocene boundary is invaluable, as they may provide evidence of possible extinction causes. For example, changes in their life histories and geographic distributions linked to potential extinction causes can be inferred from the isotopic ratios of oxygen, carbon, and strontium. Fossil remains of a juvenile mastodon from Wood County in northwest Ohio were sampled for radiocarbon dating and stable isotopic analysis. This mastodon specimen includes several skeletal elements from the hind limb and one partial tusk. The fossils were recovered in the late 19th century from a sandy beach ridge associated with ancient Lake Whittlesey, and show evidence of water transport. Accelerator Mass Spectrometry (AMS) radiocarbon dating on bioapatite from two samples of the mastodon’s femur places the mastodon within approximately 1,500 years of the Pleistocene/Holocene boundary (10,970±50 and 11,210 ±35 14C BP; 12,880 and 13,128 median cal BP). Preliminary results of stable isotopic analysis of tusk samples reveal aspects of this young mastodon’s diet and habitat. Oxygen isotopic ratios more closely match modern values than those reported from other mastodons that lived near the Last Glacial Maximum. Carbon isotopic ratios from the tusk display a diet that is notably different from that of older mastodons. This mastodon individual shows a preference for mixed feeding that approaches grazing, as opposed to the almost entirely browsing diets known from other mastodons.