Jessica Z. Metcalfe

Solving the Woolly Mammoth Conundrum: Amino Acid 15N-Enrichment Suggests a Distinct Forage or Habitat

Understanding woolly mammoth ecology is key to understanding Pleistocene community dynamics and evaluating the roles of human hunting and climate change in late Quaternary megafaunal extinctions. Previous isotopic studies of mammoths’ diet and physiology have been hampered by the ‘mammoth conundrum’: woolly mammoths have anomalously high collagen δ15N values, which are more similar to coeval carnivores than herbivores, and which could imply a distinct diet and (or) habitat, or a physiological adaptation. We analyzed individual amino acids from collagen of adult woolly mammoths and coeval species, and discovered greater  15N enrichment in source amino acids of woolly mammoths than in most other herbivores or carnivores. Woolly mammoths consumed an isotopically distinct food source, reflective of extreme aridity, dung fertilization, and (or) plant selection. This dietary signal suggests that woolly mammoths occupied a distinct habitat or forage niche relative to other Pleistocene herbivores.

Isotopic Evidence for Diet at Chau Hiix, Belize: Testing Regional Models of Hierarchy and Heterarchy

The stable carbon and nitrogen isotope values (o13C, §15N) of collagen and the carbon isotope value of structural carbonate in bioapatite were measured in the bones and teeth of Early Classic to Historic period Maya buried at Chau Hiix, Belize. Diet at Chau Hiix comprised a mixture of resources but contained an unusual amount of protein from high trophic levels. There were no differences between the diets of males and females, and there were no consistent changes in diet from birth to age 12. However, children consumed more maize than adults during all time periods. Similarities in general diet and temporal changes at Chau Hiix, Lamanai, and Altun Ha suggest their participation in a regional socioeconomic system. The diets of the highest-status Early Classic individuals at Chau Hiix, Lamanai, and Altun Ha were different from one another and from those of other individuals buried at their respective sites. We suggest that elites created or attempted to create hierarchies of food consumption within sites during the Classic period and that a heterarchy existed among elites from different sites. During the Postclassic period the major protein component of the Chau Hiix diet shifted from terrestrial animal and/or freshwater resources to reef resources, which suggests increased associations with coastal sites. Temporal changes in diet at Chau Hiix closely paralleled changes at Lamanai, but diets at the two sites were distinct during all time periods.

American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change

Significance New radiocarbon (14C) dates on American mastodon (Mammut americanum) fossils in Alaska and Yukon suggest this species suffered local extirpation before terminal Pleistocene climate changes or human colonization. Mastodons occupied high latitudes during the Last Interglacial (∼125,000–75,000 y ago) when forests were established. Ecological changes during the Wisconsinan glaciation (∼75,000 y ago) led to habitat loss and population collapse. Thereafter, mastodons were limited to areas south of the continental ice sheets, where they ultimately died out ∼10,000 14C years B.P. Extirpation of mastodons and some other megafaunal species in high latitudes was thus independent of their later extinction south of the ice. Rigorous pretreatment was crucial to removing contamination from fossils that originally yielded erroneously “young” 14C dates. Existing radiocarbon (14C) dates on American mastodon (Mammut americanum) fossils from eastern Beringia (Alaska and Yukon) have been interpreted as evidence they inhabited the Arctic and Subarctic during Pleistocene full-glacial times (∼18,000 14C years B.P.). However, this chronology is inconsistent with inferred habitat preferences of mastodons and correlative paleoecological evidence. To establish a last appearance date (LAD) for M. americanum regionally, we obtained 53 new 14C dates on 36 fossils, including specimens with previously published dates. Using collagen ultrafiltration and single amino acid (hydroxyproline) methods, these specimens consistently date to beyond or near the ∼50,000 y B.P. limit of 14C dating. Some erroneously “young” 14C dates are due to contamination by exogenous carbon from natural sources and conservation treatments used in museums. We suggest mastodons inhabited the high latitudes only during warm intervals, particularly the Last Interglacial [Marine Isotope Stage (MIS) 5] when boreal forests existed regionally. Our 14C dataset suggests that mastodons were extirpated from eastern Beringia during the MIS 4 glacial interval (∼75,000 y ago), following the ecological shift from boreal forest to steppe tundra. Mastodons thereafter became restricted to areas south of the continental ice sheets, where they suffered complete extinction ∼10,000 14C years B.P. Mastodons were already absent from eastern Beringia several tens of millennia before the first humans crossed the Bering Isthmus or the onset of climate changes during the terminal Pleistocene. Local extirpations of mastodons and other megafaunal populations in eastern Beringia were asynchrononous and independent of their final extinction south of the continental ice sheets.

White-throated sparrows adjust behaviour in response to manipulations of barometric pressure and temperature

Correlational evidence suggests that animals may use changes in barometric pressure to predict or respond to changes in weather. Birds adjust the timing of migratory flights and migratory restlessness in response to changing weather, and they make facultative movements in response to storms during winter and breeding. Using the pressure chamber of a hypobaric climatic wind tunnel we tested the responses of white-throated sparrows, Zonotrichia albicollis, to experimental changes in air pressure alone, or air pressure and temperature in combination. Sparrows in wintering (short-day) condition were exposed to gradual changes in pressure/temperature at dawn that simulated large but realistic high- and low-pressure weather systems. During a drop in pressure, birds approached their food cup more quickly and moved more often. There was no effect of increasing pressure and no additional effects of temperature change. Sparrows in spring migratory condition (photostimulated) were exposed to pressure/temperature changes in the evening. Decreases in temperature resulted in less migratory restlessness during the first hour of night, but there was no additional effect of pressure changes. These experimental results indicate that white-throated sparrows can facultatively adjust their behaviour in direct response to changing barometric pressure and temperature.

Isotopic paleoecology of Clovis mammoths from Arizona

The causes of megafaunal extinctions in North America have been widely debated but remain poorly understood. Mammoths (Mammuthus spp.) in the American Southwest were hunted by Clovis people during a period of rapid climate change, just before the regional onset of Younger Dryas cooling and mammoth extirpation. Thus, these mammoths may provide key insights into late Pleistocene extinction processes. Here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the San Pedro Valley of Arizona, using the carbon (13C/12C) and oxygen (18O/16O) isotope compositions of tooth enamel. These records suggest that Clovis mammoths experienced a warm, dry climate with sufficient summer rainfall to support seasonal C4 plant growth. Monsoon intensity may have been reduced relative to the preceding time period, but there is no isotopic evidence for severe drought. However, it is possible that the “Clovis drought”, inferred from stratigraphic evidence, occurred suddenly at the end of the animals’ lives and thus was not recorded in the enamel isotopic compositions. Unlike mammoths that lived before the Last Glacial Maximum, Clovis mammoths regularly increased C4 grass consumption during summer, probably seeking seasonally green grasslands farther from the river valley. This predictable seasonal behavior may have made mammoths easier to locate by Clovis hunters. Furthermore, Clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction.

Pleistocene Hairs: Microscopic Examination Prior to Destructive Analysis

ABSTRACT Pleistocene hairs can provide significant insights into the peopling of the Americas through isotopic and genetic analysis. Microscopic identification of isolated hairs in coprolites or sediments typically exposes hairs to mounting and/or casting media that might alter stable isotope, radiocarbon, trace element, and ancient DNA results. This paper tests the effects of such contaminants on stable carbon and nitrogen isotope analyses of hair, and describes alternative methods for preliminary hair examination. Contaminant-free methods can be used to identify growth phases, orient hairs, match broken hair fragments, identify unusual hairs for further analysis (e.g., isolated human hairs among predominantly animal remains), and preliminarily identify hairs to genus or species. This paper compares a reference collection of megafauna hairs, including mammoth (Mammuthus spp.), horse (Equus spp.), ground sloth (Nothrotheriops shastensis), and bison (Bison spp.) with isolated hairs from the late Pleistocene Colorado Plateau. Isolated hairs were attributed to mammoth, bison, and human.