The Overmyer mastodon (Mammut americanum) from Fulton County, Indiana

In June 1978 the partial skeleton of an American mastodon, Mammut americanum, was salvaged from a drainage ditch in Fulton County, north-central Indiana. The remains were recovered mostly from ca. 170–260 cm below the current land surface in marl overlain by peat and peaty marl. The stratigraphy of the site indicates that the remains were deposited in a small, open-water pond that subsequently filled. The skeleton, which is 41–48% complete, is that of a mature female, ca. 30–34 y old at death based on dental eruption and wear. Postcranial bone measurements indicate that this individual was relatively large for a female. Radiocarbon dating of wood from under the pelvis of the mastodon provided a maximum date of 12,575 ± 260 ¹⁴C y BP [15,550–13,850 cal y BP] for the animal, which is up to 2575 ¹⁴C y before the species is believed to have become extinct. Pollen samples from the site corroborate the interpretation that the regional climate was cooler and more humid than at present and supported a mixed spruce-deciduous parkland assemblage. The relatively small size of the molars of this and other mastodons from Indiana supports the hypothesis that late-glacial mastodons—just prior to their extinction—were smaller in size relative to earlier, full-glacial conspecifics. The relationship between molar size and body size is not clear, however, and there may be geographical factors as well as a temporal influence to size variation in these animals.