Home range of the Columbian mammoths (Mammuthus columbi) and grazing herbivores from the Waco Mammoth National Monument, (Texas, USA) based on strontium isotope ratios from tooth enamel bioapatite

Abstract

Waco Mammoth National Monument (WMNM) is a central Texas, Late Pleistocene fossil site dating to ~67 ka. At least 23 Columbian mammoths (Mammuthus columbi), along with the remains of 12 other vertebrate genera have been discovered at this locality. Mammoth teeth were micro-sampled at a high resolution with a computerized micromill, whereas bison and horse teeth were serially sampled with a handheld rotary tool. Serial samples from these individuals offer insights into the movement patterns (87Sr/86Sr) of WMNM herbivores. Regional vegetation and local sediments were also collected to construct an 87Sr/86Sr isoscape to track past movement of mammals, derived from Sr analyses of teeth enamel. 87Sr/86Sr in WMNM herbivores often reflects multiple grazing provenances, and sources. A series of mixing models are proposed to understand the contribution of different surface Sr sources to herbivore diets. These data indicate one mammoth spent some time at the Llano uplift area ~180 km to the SSW during the formation of molar enamel. The remaining individuals (three mammoths, a bison and a horse) lived in an area more proximal to the WMNM, ≤70 km SE of the site. 87Sr/86Sr from WMNM mammoths indicate individual fidelity to at least two geographic ranges, with at least one mammoth, potentially unrelated to the possible matriarchal herd, indicating complex population dynamics prior to mass mortality. This analysis shows that at least 25 mammals, including the horse and bison, congregated at the confluence of Brazos and Bosque rivers at ~67 ka ago, prior to their demise. A resource shortage related to drought is consistent with this pattern.