Chronology and Ecology of Late Pleistocene Megafauna in the Northern Willamette Valley, Oregon

Abstract

Since the mid-19th century, western Oregon's Willamette Valley has been a source of remains from a wide variety of extinct megafauna. Few of these have been previously described or dated, but new chronologic and isotopic analyses in conjunction with updated evaluations of stratigraphic context provide substantial new information on the species present, timing of losses, and paleoenvironmental conditions. Using subfossil material from the northern valley, we use AMS radiocarbon dating, stable isotope (δ13C and δ15N) analyses, and taxonomic dietary specialization and habitat preferences to reconstruct environments and to develop a local chronology of events that we then compare with continental and regional archaeological and paleoenvironmental data. Analysis of twelve bone specimens demonstrates the presence of bison, mammoth, horse, sloth, and mastodon from ~ 15,000–13,000 cal yr BP. The latest ages coincide with changing regional climate corresponding to the onset of the Younger Dryas. It is suggested that cooling conditions led to increased forest cover, and along with river aggradation, reduced the area of preferred habitat for the larger bodied herbivores, which contributed to the demise of local megafauna. Archaeological evidence for megafauna–human interactions in the Pacific Northwest is scarce, limiting our ability to address the human role in causing extinction.

Pre–Younger Dryas megafaunal extirpation at Rancho La Brea linked to fire-driven state shift

“…Our results also highlight the importance of considering extinction dynamics on ecologically relevant spatial, temporal, and taxonomic scales. Studies from the northeastern United States ( 2 ), the Pacific Northwest ( 52 ), and Alaska ( 54 ) have also found pre–Younger Dryas disappearances of megafauna coinciding with climate-driven environmental changes, and radiocarbon dates from the Southwestern United States indicate that megafauna may have persisted there well into the Younger Dryas (Fig. 1 and data S2).…”

“…Small populations of humans can have disproportionate impacts on landscapes through the use of fire (48); significant increases in regional fire activity after the arrival of humans have also been noted in Australia (49), New Zealand (50), Panama (51), and many other regions worldwide (52). Today, changing fire regimes resulting from climate change and human activities are again driving some ecosystems toward tipping points (53) vegetation, which affects the availability of key floral resources for animals, alters migration patterns, increases energetic costs of movement, and can put animals at higher risk of predation (53).…”

Landscape response to hydroclimate variability shown by the post-Bonneville Flood (ca. 18 ka) fluvial-geomorphic history of the middle Snake River, Idaho, USA

“…14.0 and 11.5 ka (e.g., Whitlock, 1993;Krause and Whitlock, 2013). The age of Qt1 aggradation in the Snake River and aggradation within other large rivers systems in the Pacific Northwest (e.g., Gilmour et al, 2015) also coincide with the onset of a period of global-scale cooling during the Younger Dryas stadial between 12.9-11.7 ka (Cheng et al, 2020;Fig. 8B).…”

Relationship among Plant Functional Groups, Soil, and Moisture as Basis for Wetland Conservation

“…Despite their high environmental importance, 50% of the wetlands around the world have disappeared in the last 100 years [1]. In the Willamette Valley (OR, USA), wetlands have been exposed to extensive land conversion since the 19th century because this area has fertile soil and abundant rainfall, which are significant factors for agricultural practices [2]. Before the introduction of developed agriculture, the Willamette Valley provided a broad composition of wetland habitats supporting a high diversity of native plants and animal species [3].…”