The Younger Dryas (YD; ~12.9 to 11.7 thousand years) marks an abrupt return to near-glacial conditions during the last deglaciation, yet its cause remains debated. One possible scenario, the YD impact hypothesis, proposes an extraterrestrial trigger. However, growing geochemical and stratigraphic evidence points toward a volcanic origin. This study presents the 187Os/188Os isotope and highly siderophile element (HSE) data from the Page-Ladson (PL) site (8JE591) in Florida, a well-dated, continuous sedimentary record spanning the YD onset. The onset in the PL profile is marked by unradiogenic osmium coincident with elevated Os and Re concentrations and a Cl-chondrite-normalized HSE pattern with a compositional range and signature closely matching volcanic aerosol patterns. When integrated with comparable records from Hall's Cave and the Debra L. Friedkin site in Texas, the unradiogenic 187Os/188Os ratios align across multiple depositional environments and correlate with a cluster of major bipolar volcanic eruptions (~12.98 to 12.87 thousand years) documented in Greenland and Antarctic ice cores whose cumulative radiative forcing exceeds the most volcanically active intervals of the Common Era. The magnitude and hemispheric asymmetry of this volcanic activity imply forcing of sufficient magnitude capable of disrupting the Atlantic Meridional Overturning Circulation and triggering rapid Northern Hemisphere cooling. These findings provide multiproxy, regionally consistent evidence for a volcanically driven perturbation at the onset of the YD, offering a robust alternative to impact-based explanations.

The cause, or causes, of the Pleistocene megafaunal extinctions have been difficult to establish, in part because poor spatiotemporal resolution in the fossil record hinders alignment of species disappearances with archeological and environmental data. We obtained 172 new radiocarbon dates on megafauna from Rancho La Brea in California spanning 15.6 to 10.0 thousand calendar years before present (ka). Seven species of extinct megafauna disappeared by 12.9 ka, before the onset of the Younger Dryas. Comparison with high-resolution regional datasets revealed that these disappearances coincided with an ecological state shift that followed aridification and vegetation changes during the Bølling-Allerød (14.69 to 12.89 ka). Time-series modeling implicates large-scale fires as the primary cause of the extirpations, and the catalyst of this state shift may have been mounting human impacts in a drying, warming, and increasingly fire-prone ecosystem.

Bone fragments embedded in a rib of a mastodon ( Mammut americanum ) from the Manis site, Washington, were digitally excavated and refit to reconstruct an object that is thin and broad, has smooth, shaped faces that converge to sharp lateral edges, and has a plano-convex cross section. These characteristics are consistent with the object being a human-made projectile point. The 13,900-year-old Manis projectile point is morphologically different from later cylindrical osseous points of the 13,000-year-old Clovis complex. The Manis point, which is made of mastodon bone, shows that people predating Clovis made and used osseous weapons to hunt megafauna in the Pacific Northwest during the Bølling-Allerød.

Fluting is a technological and morphological hallmark of some of the most iconic North American Paleoindian stone points. Through decades of detailed artifact analyses and replication experiments, archaeologists have spent considerable effort reconstructing how flute removals were achieved, and they have explored possible explanations of why fluting was such an important aspect of early point technologies. However, the end of fluting has been less thoroughly researched. In southern North America, fluting is recognized as a diagnostic characteristic of Clovis points dating to approximately 13,000 cal yr BP, the earliest widespread use of fluting. One thousand years later, fluting occurs more variably in Dalton and is no longer useful as a diagnostic indicator. How did fluting change, and why did point makers eventually abandon fluting? In this article, we use traditional 2D measurements, geometric morphometric (GM) analysis of 3D models, and 2D GM of flute cross sections to compare Clovis and Dalton point flute and basal morphologies. The significant differences observed show that fluting in Clovis was highly standardized, suggesting that fluting may have functioned to improve projectile durability. Because Dalton points were used increasingly as knives and other types of tools, maximizing projectile functionality became less important. We propose that fluting in Dalton is a vestigial technological trait retained beyond its original functional usefulness.

A chert object embedded in the cranium of a bison found at the Alexon site, Florida, is cited as direct evidence of human and megafauna interaction at the end of the Pleistocene in the American Southeast. Previous analyses identified the chert object as the mid-section of a lanceolate projectile point. Radiocarbon ages on unpurified bison collagen from two separate bison elements yielded Late Pleistocene and Early Holocene ages. We were able to relocate the site and examine the stratigraphy, but our attempts to radiocarbon date the bone failed. We obtained micro-computed tomography scans and used digital imaging software to generate a three-dimensional rendering of the embedded object. Finally, the skull and embedded object were visually examined. We conclude that the object embedded in the skull is not an artifact and that the Alexon site is a paleontological locality.

One of the prevailing hypotheses for the origin of the Younger Dryas (YD) cooling event is that it resulted from a bolide impact or airburst. Purported impact markers peak at or near the YD basal boundary layer at Northern Hemisphere locations. In this study, the Os-187/Os-188 ratios and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances in a well-dated sediment section through the Younger Dryas at the Debra L. Friedkin site, Texas are reported. Unradiogenic Os-187/Os-188 peaks, which could be mantle-derived or extraterrestrial, have been found above, within, and below the YD basal boundary layer. Mass balance mixing models using chondrites or iron meteorites with upper continental crust fail to duplicate the chondrite-normalized HSE patterns of the sediment samples. These HSE signatures in the Friedkin site section replicate those found in Hall's Cave, Texas. The new results here thus independently confirm that the HSE abundances in the unradiogenic Os layers are likely a fingerprint of volcanic gas aerosols derived from large Plinian eruptions and not extraterrestrial materials. To better constrain the lithological origins of YD sediments from the Friedkin and Hall's Cave sites, Texas, trace elements are presented here. The rare earth elements (REE) patterns and Ir, Ni, Ti and Zr abundances are also characterized with terrestrial signatures as opposed to impact melt rocks. An age profile correlation between the two study sites, further shows that three unradiogenic Os peaks overlap in time. The results are inconsistent with the extraterrestrial hypothesis and support instead an episodic and volcanic origin for the observed geochemical anomalies at the Debra L. Fried kin and Hall's Cave sites, Texas. (C) 2021 Elsevier Ltd. All rights reserved.

Hall's Cave, Texas, contains a radiocarbon dated sediment record extending from the Last Glacial Maximum through the Holocene. Changes in the characteristics of the sediments and the pattern of sedimentation in the cave correlate with environmental and climatic shifts over the last 20,000 years. The sediments in Hall's Cave preserve well-documented paleontological and paleoecological records. We show that the cave sediments also contain a well-preserved archaeological record dating from similar to 10,500 cal yr B.P. to the Historic period. Human use of the cave was episodic and tied to environmental factors, with evidence for increasingly intensive use of the cave throughout the Holocene. Episodes of deposition and non-deposition in Hall's Cave were synchronous with periods of deposition and erosion in low-order streams of the Edwards Plateau. These processes structured the archaeological record of central Texas. (C) 2021 The Author(s). Published by Elsevier Ltd.

Thirty-two radiocarbon ages on bone, charcoal, and carbonized plant remains from 10 Clovis sites range from 11,110 ± 40 to 10,820 ± 10 14C years before the present (yr B.P.). These radiocarbon ages provide a maximum calibrated (cal) age range for Clovis of ~13,050 to ~12,750 cal yr B.P. This radiocarbon record suggests that Clovis first appeared at the end of the Allerød and is one of at least three contemporary archaeological complexes in the Western Hemisphere during the terminal Pleistocene. Stemmed projectile points in western North America are coeval and even older than Clovis, and the Fishtail point complex is well established in the southern cone of South America by ~12,900 cal yr B.P. Clovis disappeared ~12,750 cal yr B.P. at the beginning of the Younger Dryas, coincident with the extinction of the remaining North American megafauna (Proboscideans) and the appearance of multiple North American regional archaeological complexes.

In April 2018, the Center for the Study of the First Americans, Hakai Institute, and University of Victoria co-sponsored a five-day workshop investigating the origins of Western Stemmed technologies and their relationship with other Paleoindian and Paleolithic technocomplexes of far western North America, Beringia, and northeast Asia. This Perspective introduces the proceedings of the workshop, which are presented as a series of longer essays in this special issue of PaleoAmerica. The workshop was funded through an endowment created by Robert and Sharon Wilson at Texas A&M University to support the continued multidisciplinary investigation of the peopling of the Americas and dissemination of scientific results to the professional community and the public.

The early archaeological record of Beringia is complicated by the occurrence of several lithic industries. Site assemblages, dating from 14,000 to 12,800 years ago and located from the Yana-Indigirka Lowlands of Siberia to the upper Tanana River basin, contain artifacts characteristic of the Nenana technological complex. After 12,800 years ago, site assemblages contain artifacts diagnostic of the Denali technocomplex. To explain the variation in lithic industries, we first and foremost need well-stratified and well-dated sites with multiple components so we securely know their ages and depositional relationships. We present excavation results of one such site located in interior Alaska, Owl Ridge, with the goal of assessing site stratigraphy, radiocarbon chronology, and natural site formation processes. Owl Ridge was visited three times during the Pleistocene-Holocene transition with a Nenana-complex occupation at 13,380-12,800 years ago followed by two Denali-complex occupations at 12,540-11,430 years ago and 11,270-11,200 years ago. Assemblage change at Owl Ridge was diachronically patterned, as at the nearby Dry Creek archaeological site, and separated by two climatic events, a brief extremely windy Younger Dryas (lasting 300-250 years) and a very brief wetter period (lasting similar to 160 years). Our results indicate these climate and environmental conditions played a role in settlement of eastern Beringia.

The Younger Dryas (YD) abrupt cooling event ca. 12.9 +/- 0.1 ka is associated with substantial meltwater input into the North Atlantic Ocean, reversing deglacial warming. One controversial and prevailing hypothesis is that a bolide impact or airburst is responsible for these environmental changes. Here, highly siderophile element (HSE; Os, Ir, Ru, Pt, Pd, and Re) abundances and Os-187/ Os-188 ratios were obtained in a well-dated sediment section at Hall's Cave, TX, USA to test this hypothesis. In Hall's Cave, layers below, above, and in the YD have Os-187/ Os-188 ratios consistent with incorporation of extraterrestrial or mantle-derived material. The HSE abundances indicate that these layers contain volcanic gas aerosols and not extraterrestrial materials. The most likely explanation is that episodic, distant volcanic emissions were deposited in Hall's Cave sediments. Coupled Os-187/ Os-188 ratios and HSE concentration data at close stratigraphic intervals are required to effectively differentiate between bolide and volcanic origins.

Large-scale changes in global climate at the end of the Pleistocene significantly impacted ecosystems across North America. However, the pace and scale of biotic turnover in response to both the Younger Dryas cold period and subsequent Holocene rapid warming have been challenging to assess because of the scarcity of well dated fossil and pollen records that covers this period. Here we present an ancient DNA record from Hall's Cave, Texas, that documents 100 vertebrate and 45 plant taxa from bulk fossils and sediment. We show that local plant and animal diversity dropped markedly during Younger Dryas cooling, but while plant diversity recovered in the early Holocene, animal diversity did not. Instead, five extant and nine extinct large bodied animals disappeared from the region at the end of the Pleistocene. Our findings suggest that climate change affected the local ecosystem in Texas over the Pleistocene-Holocene boundary, but climate change on its own may not explain the disappearance of the megafauna at the end of the Pleistocene.

The Page-Ladson site, currently buried and submerged in a sinkhole in northwestern Florida, demonstrates evidence of human occupation in North America by 14,550 calendar years ago (cal yr BP). This paper combines new diatom evidence with existing palynological data to strengthen paleoenvironmental interpretations at the site. The Page-Ladson sinkhole was not entirely submerged between similar to 15,100 and 14,400 cal yr BP. Conditions at the site became warmer and wetter, and the sinkhole became a turbid pond from similar to 14,400 to 12,900 cal yr BP. From similar to 12,900 cal yr BP until similar to 11,000 cal yr BP, a disappearance of diatoms in the coring location suggests the sinkhole margin was dry. Water levels rose between 11,000 and 9000 cal yr BP, submerging the coring location on the pond margin. These environmental data help contextualize the archaeological data in the region.

Forty years ago, Knut Fladmark (1979) argued that the Pacific Coast offered a viable alternative to the ice-free corridor model for the initial peopling of the Americas—one of the first to support a “coastal migration theory” that remained marginal for decades. Today, the pre-Clovis occupation at the Monte Verde site is widely accepted, several other pre-Clovis sites are well documented, investigations of terminal Pleistocene subaerial and submerged Pacific Coast landscapes have increased, and multiple lines of evidence are helping decode the nature of early human dispersals into the Americas. Misconceptions remain, however, about the state of knowledge, productivity, and deglaciation chronology of Pleistocene coastlines and possible technological connections around the Pacific Rim. We review current evidence for several significant clusters of early Pacific Coast archaeological sites in North and South America that include sites as old or older than Clovis. We argue that stemmed points, foliate points, and crescents (lunates) found around the Pacific Rim may corroborate genomic studies that support an early Pacific Coast dispersal route into the Americas. Still, much remains to be learned about the Pleistocene colonization of the Americas, and multiple working hypotheses are warranted.

Drivers of Late Quaternary megafaunal extinctions are relevant to modern conservation policy in a world of growing human population density, climate change, and faunal decline. Traditional debates tend toward global solutions, blaming either dramatic climate change or dispersals of Homo sapiens to new regions. Inherent limitations to archaeological and paleontological data sets often require reliance on scant, poorly resolved lines of evidence. However, recent developments in scientific technologies allow for more local, context-specific approaches. In the present article, we highlight how developments in five such methodologies (radiocarbon approaches, stable isotope analysis, ancient DNA, ancient proteomics, microscopy) have helped drive detailed analysis of specific megafaunal species, their particular ecological settings, and responses to new competitors or predators, climate change, and other external phenomena. The detailed case studies of faunal community composition, extinction chronologies, and demographic trends enabled by these methods examine megafaunal extinctions at scales appropriate for practical understanding of threats against particular species in their habitats today.

North and South America were the last continents to be explored and settled by modern humans at the end of the Pleistocene. Genetic data, derived from contemporary populations and ancient individuals, show that the first Americans originated from Asia and after several population splits moved south of the continental ice sheets that covered Canada sometime between ~17.5 and ~14.6 thousand years (ka) ago. Archaeological evidence shows that geographically dispersed populations lived successfully, using biface, blade, and osseous technologies, in multiple places in North and South America between ~15.5 and ~14 ka ago. Regional archaeological complexes emerged by at least ~13 ka ago in North America and ~12.9 ka ago in South America. Current genetic and archaeological data do not support an earlier (pre-17.5 ka ago) occupation of the Americas.