Seeds of controversy: Ecology, depositional context, and radiocarbon dating of Ruppia cirrhosa at the White Sands trackway

Abstract

Context and chronology are fundamental in archaeological studies, and without rigorous standards in both fieldwork and analysis, researchers risk drawing faulty conclusions. The role of submerged aquatic plants in radiocarbon dating is a case in point. For example, research at White Sands National Park, New Mexico, has dated fossil human and megafauna trackways using Ruppia cirrhosa (Ruppia) seeds. Some studies, such as Pigati et al. (2024), argue that there are no site formation issues with the Ruppia seed layers used to date the ancient footprints at White Sands Locality-2 (WHSA-2) and that the hard water effect has not impacted their radiocarbon dating. These assertions have significant implications for understanding broader issues like the peopling of the Americas. However, we disagree with these claims, emphasizing the importance of understanding the physical context of the Ruppia seed layers at WHSA-2—whether the plants grew in situ or were transported—and the ecological requirements of Ruppia. These issues remain unresolved. Additionally, the potential impacts of physical mixing and the hard water effect on radiocarbon dates have been largely overlooked. In this paper, we examine both the ecology and depositional context of Ruppia and discuss why the Ruppia seeds at Paleolake Otero still present challenges for radiocarbon dating.