Russell W. Graham

Spatial Response of Mammals to Late Quaternary Environmental Fluctuations

Analyses of fossil mammal faunas from 2945 localities in the United States demonstrate that the geographic ranges of individual species shifted at different times, in different directions, and at different rates in response to late Quaternary environmental fluctuations. The geographic pattern of faunal provinces was similar for the late Pleistocene and late Holocene, but differing environmental gradients resulted in dissimilar species composition for these biogeographic regions. Modern community patterns emerged only in the last few thousand years, and many late Pleistocene communities do not have modern analogs. Faunal heterogeneity was greater in the late Pleistocene.

Kimmswick: A Clovis-Mastodon Association in Eastern Missouri

Stone tools characteristic of the Clovis culture have been found in direct association with bones of the American mastodon at Kimmswick, Missouri. The vertebrate fauna from Clovis components suggests a deciduous woodland and meadow habitat. Such an environmental reconstruction provides a new perspective for Clovis adaptations and the ecological tolerances of Mammut americanum.

A catastrophic kill of ice-trapped coots; time-averaged versus scavenger-specific disarticulation patterns

More than 300 coots ( Fulica americana ) became frozen in Spring Lake, Tazewell County, Illinois, on December 1, 1985. This catastrophic event permitted 8 weeks of taphonomic observations, which showed that ice forms a stable substrate which permits terrestrial taphonomic processes to be imprinted on lacustrine deposits. Bird and mammal scavengers attacked coot carcasses in different manners, resulting in distinct disarticulation sequences. Bird scavengers preferentially fed on the head, neck, and breast-wing complex, causing early disarticulation of bones in these areas, late loss of hindlimb joints, and minimal bone damage. In contrast, mammal scavengers concentrated their attention on the hindlimb and tail region, resulting in bone breakage and early disarticulation of these body parts, but late disarticulation of the breast-wing complex. These data demonstrate that scavenger-specific feeding behaviors significantly influence disarticulation patterns early in assemblage formation, while anatomy may exert increasingly greater influence on disarticulation patterns as carasses become less attractive to scavengers. Finally, because taphonomic processes change in intensity and type through time, bone frequency and modification patterns will vary according to the time at which the patterns are arrested by burial. Thus, bone frequency and modification patterns should provide an index to the relative importance of specific biotic agents and of anatomy in fossil disarticulation patterns as well as an estimate of the time between death and burial.

Quantifying the extent of North American mammal extinction relative to the pre-anthropogenic baseline.

Earth has experienced five major extinction events in the past 450 million years. Many scientists suggest we are now witnessing a sixth, driven by human impacts. However, it has been difficult to quantify the real extent of the current extinction episode, either for a given taxonomic group at the continental scale or for the worldwide biota, largely because comparisons of pre-anthropogenic and anthropogenic biodiversity baselines have been unavailable. Here, we compute those baselines for mammals of temperate North America, using a sampling-standardized rich fossil record to reconstruct species-area relationships for a series of time slices ranging from 30 million to 500 years ago. We show that shortly after humans first arrived in North America, mammalian diversity dropped to become at least 15%–42% too low compared to the “normal” diversity baseline that had existed for millions of years. While the Holocene reduction in North American mammal diversity has long been recognized qualitatively, our results provide a quantitative measure that clarifies how significant the diversity reduction actually was. If mass extinctions are defined as loss of at least 75% of species on a global scale, our data suggest that North American mammals had already progressed one-fifth to more than halfway (depending on biogeographic province) towards that benchmark, even before industrialized society began to affect them. Data currently are not available to make similar quantitative estimates for other continents, but qualitative declines in Holocene mammal diversity are also widely recognized in South America, Eurasia, and Australia. Extending our methodology to mammals in these areas, as well as to other taxa where possible, would provide a reasonable way to assess the magnitude of global extinction, the biodiversity impact of extinctions of currently threatened species, and the efficacy of conservation efforts into the future.

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.

EFFECTS OF ECOLOGICAL AND PALEOECOLOGICAL PATTERNS ON SUBSISTENCE AND PALEOENVIRONMENTAL RECONSTRUCTIONS

Archaeology is presently evolving to show a more interdisciplinary approach by its researchers, an attitude which is reflected in greater consideration of the physical environment and increasing interaction with the work of allied scientists such as geologists and paleoecologists. It is increasingly accepted that human populations form a living ecosystem, tied to their environment and responding to the same types of external regulatory mechanisms as other organisms, though in part adapting to environmental change by cultural evolution (Ford 1977). The problems inherent in successfully integrating and synthesizing multidisciplinary data into an interdisciplinary product have been discussed by Butzer (1975), while Rhoades (1978) issued a much needed warning about the dangers of oversimplifying ecological concepts when applying them to archaeological situations. In this paper we discuss the development of these concepts and attempt to clarify their present status and to evaluate their pertinence to archaeological problems. Our viewpoint is that of paleoecologists who frequently work with archaeologists on problems of mutual interest, and as such it may offer some new ideas to the archaeologist himself working with such data. One of the goals of ecology is to ascertain the causes of distribution and abundance of organisms. This field concerns itself not only with single organisms, but with populations, with biotic communities of numerous species, and with ecosystems which include both the biotic community and its abiotic environment. If it is difficult to study an organism without taking into account its biotic and physical environment, it is nearly impossible to study a community without first knowing something about the organisms of which it is comprised. Archaeology is tied closely to the study of communities and ecosystems since it deals with sequences of social and cultural evolution under diverse environments.

Paleoenvironmental implications of the Quaternary distribution of the eastern chipmunk (Tamias striatus) in central Texas

Abstract Four Quaternary cave sites in central Texas demonstrate that the eastern chipmunk ( Tamias striatus ) ranged more than 600 km southwest of its modern distribution. Climatographs suggest that the late Pleistocene/early Holocene summer climates were either 7.5°C cooler and 120 mm moister than today or 300 mm moister, if temperature remained unchanged. The distribution of T. striatus also implies that mixed deciduous forest existed on the eastern Edwards Plateau at this time.

Collateral mammal diversity loss associated with late Quaternary megafaunal extinctions and implications for the future

Abstract Using data from two palaeontological databases, MIOMAP and FAUNMAP (now linked as NEOMAP), we explore how late Quaternary species loss compared in large and small mammals by determining palaeospecies-area relationships (PSARs) at 19 temporal intervals ranging from c. 30 million to 500 years ago in 10 different biogeographical provinces in the USA. We found that mammalian diversity of both large and small mammals remained relatively stable from 30 million years ago up until both crashed near the Pleistocene–Holocene transition. The diversity crash had two components: the well-known megafaunal extinction that amounted to c. 21% of the pre-crash species, and collateral biodiversity loss due to biogeographical range reductions. Collateral loss resulted in large mammal diversity regionally falling an additional 6–31% above extinction loss, and small mammal diversity falling 16–51%, even though very few small mammals suffered extinction. These results imply that collateral losses due to biogeographical range adjustments may effectively double the regional diversity loss during an extinction event, substantially magnifying the ecological ramifications of the extinctions themselves. This is of interest in forecasting future ecological impacts of mammal extinctions, given that c. 8% of USA mammal species, and 22% of mammal species worldwide, are now considered ‘Threatened’ by the IUCN.

Ancient DNA supports southern survival of Richardson's collared lemming (Dicrostonyx richardsoni) during the last glacial maximum

Collared lemmings (genus Dicrostonyx) are circumpolar Arctic arvicoline rodents associated with tundra. However, during the last glacial maximum (LGM), Dicrostonyx lived along the southern ice margin of the Laurentide ice sheet in communities comprising both temperate and boreal species. To better understand these communities and the fate of these southern individuals, we compare mitochondrial cytochrome b sequence data from three LGM‐age Dicrostonyx fossils from south of the Laurentide ice sheet to sequences from modern Dicrostonyx sampled from across their present‐day range. We test whether the Dicrostonyx populations from LGM‐age continental USA became extinct at the Pleistocene–Holocene transition ~11000 years ago or, alternatively, if they belong to an extant species whose habitat preferences can be used to infer the palaeoclimate along the glacial margin. Our results indicate that LGM‐age Dicrostonyx from Iowa and South Dakota belong to Dicrostonyx richardsoni, which currently lives in a temperate tundra environment west of Hudson Bay, Canada. This suggests a palaeoclimate south of the Laurentide ice sheet that contains elements similar to the more temperate shrub tundra characteristic of extant D. richardsoni habitat, rather than the very cold, dry tundra of the Northern Arctic. While more data are required to determine whether or not the LGM southern population is ancestral to extant D. richardsoni, it seems most probable that the species survived the LGM in a southern refugium.

The spatial response of mammals to Quaternary climate changes

The Quaternary was characterized by rapid climatic fluctuations (Dansgaard et al. 1993) which had dramatic effects on terrestrial biotas, especially the mammalian fauna (Graham & Mead 1987). These climatic events controlled the composition and spatial distribution of continental mammal faunas by regulating intercontinental movements, by driving intracontinental shifts in the geographic distributions of species, and by creating environmental conditions for diversification and extinction. For this discussion, I will focus only on intercontinental and intracontinental movements of species. Diversification (evolution) and extinction are covered, respectively, by Lister (1996) and Sher (1996).