Brendan J. Culleton

Development and Disintegration of Maya Political Systems in Response to Climate Change

Maya and Climate Climate has affected the vitality of many different societies in the past, as shown by numerous records across the globe and throughout human history. One of the most obvious and spectacular examples of this is from the Classic Maya civilization, whose advanced culture left highly detailed records of all aspects of their existence between 300 and 1000 C.E. Kennett et al. (p. 788; see the cover) present a detailed climate record derived from a stalagmite collected from a cave in Belize, in the midst of the Classic Maya settlement. The fine resolution and precise dating of the record allows changes in precipitation to be related to the politics, war, and population fluctuations of the Mayans. A record of rainfall from a stalagmite in southern Belize provides a context for better understanding Maya civilization. The role of climate change in the development and demise of Classic Maya civilization (300 to 1000 C.E.) remains controversial because of the absence of well-dated climate and archaeological sequences. We present a precisely dated subannual climate record for the past 2000 years from Yok Balum Cave, Belize. From comparison of this record with historical events compiled from well-dated stone monuments, we propose that anomalously high rainfall favored unprecedented population expansion and the proliferation of political centers between 440 and 660 C.E. This was followed by a drying trend between 660 and 1000 C.E. that triggered the balkanization of polities, increased warfare, and the asynchronous disintegration of polities, followed by population collapse in the context of an extended drought between 1020 and 1100 C.E.

Paleoindian Seafaring, Maritime Technologies, and Coastal Foraging on California’s Channel Islands

Archaeological sites reveal a variety of tools used to hunt marine birds, mammals, and fish 12,000 years ago. Three archaeological sites on California’s Channel Islands show that Paleoindians relied heavily on marine resources. The Paleocoastal sites, dated between ~12,200 and 11,200 years ago, contain numerous stemmed projectile points and crescents associated with a variety of marine and aquatic faunal remains. At site CA-SRI-512 on Santa Rosa Island, Paleocoastal peoples used such tools to capture geese, cormorants, and other birds, along with marine mammals and finfish. At Cardwell Bluffs on San Miguel Island, Paleocoastal peoples collected local chert cobbles, worked them into bifaces and projectile points, and discarded thousands of marine shells. With bifacial technologies similar to those seen in Western Pluvial Lakes Tradition assemblages of western North America, the sites provide evidence for seafaring and island colonization by Paleoindians with a diversified maritime economy.

Intrashell Radiocarbon Variability in Marine Mollusks

We demonstrate variable radiocarbon content within 2 historic (AD 1936) and 2 prehistoric (about 8200 BP and 3500 BP) Mytilus californianus shells from the Santa Barbara Channel region, California, USA. Historic specimens from the mainland coast exhibit a greater range of intrashell variability (i.e. 180-240 14C yr) than archaeological specimens from Daisy Cave on San Miguel Island (i.e. 120 14C yr in both shells). δ13C and δ18O profiles are in general agreement with the upwelling of deep ocean water depleted in 14C as a determinant of local marine reservoir correction (∆R) in the San Miguel Island samples. Upwelling cycles are difficult to identify in the mainland specimens, where intrashell variations in 14C content may be a complex product of oceanic mixing and periodic seasonal inputs of 14C-depeleted terrestrial runoff. Though the mechanisms controlling ∆R at subannual to annual scales are not entirely clear, the fluctuations represent significant sources of random dating error in marine environments, particularly if a small section of shell is selected for accelerator mass spec- trometry (AMS) dating. For maximum precision and accuracy in AMS dating of marine shells, we recommend that archae- ologists, paleontologists, and 14C lab personnel average out these variations by sampling across multiple increments of growth.

Late Pleistocene Human Skeleton and mtDNA Link Paleoamericans and Modern Native Americans

American Beauty Modern Native American ancestry traces back to an East Asian migration across Beringia. However, some Native American skeletons from the late Pleistocene show phenotypic characteristics more similar to other, more geographically distant, human populations. Chatters et al. (p. 750) describe a skeleton with a Paleoamerican phenotype from the eastern Yucatan, dating to approximately 12 to 13 thousand years ago, with a relatively common extant Native American mitochondrial DNA haplotype. The Paleoamerican phenotype may thus have evolved independently among Native American populations. The differences between Paleoamericans and Native Americans likely resulted from local evolution. Because of differences in craniofacial morphology and dentition between the earliest American skeletons and modern Native Americans, separate origins have been postulated for them, despite genetic evidence to the contrary. We describe a near-complete human skeleton with an intact cranium and preserved DNA found with extinct fauna in a submerged cave on Mexico’s Yucatan Peninsula. This skeleton dates to between 13,000 and 12,000 calendar years ago and has Paleoamerican craniofacial characteristics and a Beringian-derived mitochondrial DNA (mtDNA) haplogroup (D1). Thus, the differences between Paleoamericans and Native Americans probably resulted from in situ evolution rather than separate ancestry.

Human impacts on Nearshore Shellfish Taxa: a 7,000 year record from Santa Rosa Island, California

Within the broad framework of historical and behavioral ecology, we analyzed faunal remains from a large habitation site (CA-SRI-147) on Santa Rosa Island to explore a 7,000 year record of coastal subsistence, nearshore ecological dynamics, and human impacts on shellfish populations. This long, stratified sequence provides a rare opportunity to study the effects of prolonged human predation on local intertidal and nearshore habitats. During the past 7,000 years, the Island Chumash and their predecessors had significant impacts on nearshore ecosystems, caused by growing human populations and depletion of marine and terrestrial ecosystems. At CA-SRI-147, local depletion of higher ranked shellfish species stimulated dietary expansion and a heavier reliance on lower-ranked shellfish taxa and more intensive exploitation of nearshore and pelagic fishes. In the Late Holocene, as local ecosystems were increasingly depleted, the Island Chumash relied increasingly on craft specialization and trade to meet their subsistence needs. Native peoples clearly impacted Channel Island ecosystems, but data from CA-SRI-147 suggest that they adjusted their subsistence strategies toward productive fisheries that sustained the high population densities and sociopolitical complexity recorded by early Spanish chroniclers at European contact.

Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (≈12,900 ± 100 cal BP or 10,900 ± 100 14C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to ≈12,950 ± 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event, further strengthened by its co-occurrence with other nanometer-sized diamond polymorphs (n-diamonds and cubics). These shock-synthesized diamonds are also associated with proxies indicating major biomass burning (charcoal, carbon spherules, and soot). This biomass burning at the Younger Dryas (YD) onset is regional in extent, based on evidence from adjacent Santa Barbara Basin and coeval with broader continent-wide biomass burning. Biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths (Mammuthus exilis) on the Channel Islands, correlating with broader animal extinctions throughout North America. The only previously known co-occurrence of nanodiamonds, soot, and extinction is the Cretaceous-Tertiary (K/T) impact layer. These data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over North America at ≈12,900 ± 100 cal BP.

Early procurement of scarlet macaws and the emergence of social complexity in Chaco Canyon, NM

Significance New accelerator mass spectrometer (AMS) 14C dates of scarlet macaw (Ara macao) skeletons from Chaco Canyon in northwestern New Mexico reveal the earliest (A.D. 900–975) direct evidence for procurement of this Neotropical species by Pueblo people from Mesoamerica. By directly dating the macaws, we demonstrate the existence of long-distance acquisition networks throughout much (A.D. 900–1150) of Chaco’s history. In contrast to models of societal evolution that attribute procurement of macaws to the 11th-century peak of Chacoan influence and architectural expansion, most 14C dates significantly predate this period. We propose that access to and control of these important status markers from Mesoamerica before A.D. 1040 was thus linked to the early formalization of social hierarchy in Chaco. High-precision accelerator mass spectrometer (AMS) 14C dates of scarlet macaw (Ara macao) skeletal remains provide the first direct evidence from Chaco Canyon in northwestern New Mexico that these Neotropical birds were procured from Mesoamerica by Pueblo people as early as ∼A.D. 900–975. Chaco was a prominent prehistoric Pueblo center with a dense concentration of multistoried great houses constructed from the 9th through early 12th centuries. At the best known great house of Pueblo Bonito, unusual burial crypts and significant quantities of exotic and symbolically important materials, including scarlet macaws, turquoise, marine shell, and cacao, suggest societal complexity unprecedented elsewhere in the Puebloan world. Scarlet macaws are known markers of social and political status among the Pueblos. New AMS 14C-dated scarlet macaw remains from Pueblo Bonito demonstrate that these birds were acquired persistently from Mesoamerica between A.D. 900 and 1150. Most of the macaws date before the hypothesized apogeal Chacoan period (A.D. 1040–1110) to which they are commonly attributed. The 10th century acquisition of these birds is consistent with the hypothesis that more formalized status hierarchies developed with significant connections to Mesoamerica before the post-A.D. 1040 architectural florescence in Chaco Canyon.

Archaeogenomic evidence reveals prehistoric matrilineal dynasty

For societies with writing systems, hereditary leadership is documented as one of the hallmarks of early political complexity and governance. In contrast, it is unknown whether hereditary succession played a role in the early formation of prehistoric complex societies that lacked writing. Here we use an archaeogenomic approach to identify an elite matriline that persisted between 800 and 1130 CE in Chaco Canyon, the centre of an expansive prehistoric complex society in the Southwestern United States. We show that nine individuals buried in an elite crypt at Pueblo Bonito, the largest structure in the canyon, have identical mitochondrial genomes. Analyses of nuclear genome data from six samples with the highest DNA preservation demonstrate mother–daughter and grandmother–grandson relationships, evidence for a multigenerational matrilineal descent group. Together, these results demonstrate the persistence of an elite matriline in Chaco for ∼330 years.

Timing and causes of mid-Holocene mammoth extinction on St. Paul Island, Alaska

Significance St. Paul Island, Alaska, is famous for its late-surviving population of woolly mammoth. The puzzle of mid-Holocene extinction is solved via multiple independent paleoenvironmental proxies that tightly constrain the timing of extinction to 5,600 ± 100 y ago and strongly point to the effects of sea-level rise and drier climates on freshwater scarcity as the primary extinction driver. Likely ecosystem effects of the mega-herbivore extinction include reduced rates of watershed erosion by elimination of crowding around water holes and a vegetation shift toward increased abundances of herbaceous taxa. Freshwater availability may be an underappreciated driver of island extinction. This study reinforces 21st-century concerns about the vulnerability of island populations, including humans, to future warming, freshwater availability, and sea level rise. Relict woolly mammoth (Mammuthus primigenius) populations survived on several small Beringian islands for thousands of years after mainland populations went extinct. Here we present multiproxy paleoenvironmental records to investigate the timing, causes, and consequences of mammoth disappearance from St. Paul Island, Alaska. Five independent indicators of extinction show that mammoths survived on St. Paul until 5,600 ± 100 y ago. Vegetation composition remained stable during the extinction window, and there is no evidence of human presence on the island before 1787 CE, suggesting that these factors were not extinction drivers. Instead, the extinction coincided with declining freshwater resources and drier climates between 7,850 and 5,600 y ago, as inferred from sedimentary magnetic susceptibility, oxygen isotopes, and diatom and cladoceran assemblages in a sediment core from a freshwater lake on the island, and stable nitrogen isotopes from mammoth remains. Contrary to other extinction models for the St. Paul mammoth population, this evidence indicates that this mammoth population died out because of the synergistic effects of shrinking island area and freshwater scarcity caused by rising sea levels and regional climate change. Degradation of water quality by intensified mammoth activity around the lake likely exacerbated the situation. The St. Paul mammoth demise is now one of the best-dated prehistoric extinctions, highlighting freshwater limitation as an overlooked extinction driver and underscoring the vulnerability of small island populations to environmental change, even in the absence of human influence.

Bayesian Analysis of High-Precision AMS 14C Dates from a Prehistoric Mexican Shellmound

We establish a precision accelerator mass spectrometry (AMS) radiocarbon chronology for the Archaic period Tlacuachero shellmound (Chiapas, Mexico) within a Bayesian statistical framework. Carbonized twig samples were sequentially selected from well-defined stratigraphic contexts based on iterative improvements to a probabilistic chronological model. Analytical error for these measurements is ±15 to 20 14C yr. This greater precision and the absence of stratigraphic reversals eclipses previous 14C work at the site. Based on this, we establish a chronological framework for a sequence of 3 clay floors dating to between 4930 and 4270 cal BP and determine that the bedded shell deposits that formed the mound accumulated rapidly during 2 episodes: a lower 2-m section below the floors that accumulated over a 0?150 cal yr period at 5050-4875 cal BP and, an upper 3.5-m section above the floors that accumulated over a 0-80 cal yr period at 4380-4230 cal BP.