Bluefish Caves Research Articles

Experiments suggest rockfall an improbable cause for bone surface modification on 24,000-year-old bone at Bluefish Caves, Canada

At Bluefish Caves in the Yukon Territory of Canada, researchers argue that 24,000-year-old faunal remains bear anthropogenic cutmarks, and provide evidence of a pre-Last Glacial Maximum (23-18 ka) human occupation of North America's arctic. However, non-anthropogenic agents can also leave marks on bones that might resemble bone surface modifications (BSMs) produced by stone tools. Here we test the hypothesis that rockfall traces can mimic stone tool cutmarks by experimentally replicating the spalling limestone shelter at Bluefish Caves, dropping variably sized limestone blocks (12–2322 g) from 3.5 m onto Bovidae remains. These same bones were subsequently sliced with stone tools to produce cutmarks for comparison. The resulting marks were analyzed with a Dino-Lite microscope and a Sensofar S Neox 3-D optical profilometer to allow quantitative comparisons of their morphologies. Results show that cutmarks can be distinguished from rockfall damage, and do not support the hypothesis that the BSM previously identified as cutmarks at Bluefish Caves are instead a product of rockfall.

Horse exploitation by Beringian hunters during the Last Glacial Maximum

Genetic data suggest that the Native American founder population diverged from its Asian parent population about 25,000 years ago and was geographically isolated during the Last Glacial Maximum (LGM, ca. 21,000 years BP) before dispersing into North and South America as the ice sheets retreated. Archaeological evidence in eastern Siberia and Beringia is scarce, however. Although stone tools and cutmarks on bones dated to the LGM are reported at Bluefish Caves (Yukon Territory, Canada), the stratigraphic integrity of the site and the interpretation of the bone modifications have long been questioned by the scientific community. Here, we describe the results of a zooarchaeological study of the faunal assemblages from Pleistocene loess deposits of Bluefish Caves 1 and 2. Taphonomic analyses indicate that humans hunted a variety of prey at the site, including the Beringian horse (E. lambei), as early as 23,500 years BP. We discuss the significance of the site in debates about the timing of the initial peopling of North America and the role of human-hunters in megafaunal extinctions.

Unresolved Questions about Site Formation, Provenience, and the Impact of Natural Processes on Bone at the Bluefish Caves, Yukon Territory

Unresolved Questions about Site Formation, Provenience, and the Impact of Natural Processes on Bone at the Bluefish Caves, Yukon Territory

Cheek tooth morphology and ancient mitochondrial DNA of late Pleistocene horses from the western interior of North America: Implications for the taxonomy of North American Late Pleistocene Equus.

Horses were a dominant component of North American Pleistocene land mammal communities and their remains are well represented in the fossil record. Despite the abundant material available for study, there is still considerable disagreement over the number of species of Equus that inhabited the different regions of the continent and on their taxonomic nomenclature. In this study, we investigated cheek tooth morphology and ancient mtDNA of late Pleistocene Equus specimens from the Western Interior of North America, with the objective of clarifying the species that lived in this region prior to the end-Pleistocene extinction. Based on the morphological and molecular data analyzed, a caballine (Equus ferus) and a non-caballine (E. conversidens) species were identified from different localities across most of the Western Interior. A second non-caballine species (E. cedralensis) was recognized from southern localities based exclusively on the morphological analyses of the cheek teeth. Notably the separation into caballine and non-caballine species was observed in the Bayesian phylogenetic analysis of ancient mtDNA as well as in the geometric morphometric analyses of the upper and lower premolars. Teeth morphologically identified as E. conversidens that yielded ancient mtDNA fall within the New World stilt-legged clade recognized in previous studies and this is the name we apply to this group. Geographic variation in morphology in the caballine species is indicated by statistically different occlusal enamel patterns in the specimens from Bluefish Caves, Yukon Territory, relative to the specimens from the other geographic regions. Whether this represents ecomorphological variation and/or a certain degree of geographic and genetic isolation of these Arctic populations requires further study.

Earliest Human Presence in North America Dated to the Last Glacial Maximum: New Radiocarbon Dates from Bluefish Caves, Canada.

The timing of the first entry of humans into North America is still hotly debated within the scientific community. Excavations conducted at Bluefish Caves (Yukon Territory) from 1977 to 1987 yielded a series of radiocarbon dates that led archaeologists to propose that the initial dispersal of human groups into Eastern Beringia (Alaska and the Yukon Territory) occurred during the Last Glacial Maximum (LGM). This hypothesis proved highly controversial in the absence of other sites of similar age and concerns about the stratigraphy and anthropogenic signature of the bone assemblages that yielded the dates. The weight of the available archaeological evidence suggests that the first peopling of North America occurred ca. 14,000 cal BP (calibrated years Before Present), i.e., well after the LGM. Here, we report new AMS radiocarbon dates obtained on cut-marked bone samples identified during a comprehensive taphonomic analysis of the Bluefish Caves fauna. Our results demonstrate that humans occupied the site as early as 24,000 cal BP (19,650 ± 130 14C BP). In addition to proving that Bluefish Caves is the oldest known archaeological site in North America, the results offer archaeological support for the “Beringian standstill hypothesis”, which proposes that a genetically isolated human population persisted in Beringia during the LGM and dispersed from there to North and South America during the post-LGM period.

Pleistocene vertebrates of the Yukon Territory

Unglaciated parts of the Yukon constitute one of the most important areas in North America for yielding Pleistocene vertebrate fossils. Nearly 30 vertebrate faunal localities are reviewed spanning a period of about 1.6 Ma (million years ago) to the close of the Pleistocene some 10 000 BP (radiocarbon years before present, taken as 1950). The vertebrate fossils represent at least 8 species of fishes, 1 amphibian, 41 species of birds and 83 species of mammals. Dominant among the large mammals are: steppe bison ( Bison priscus), horse ( Equus sp.), woolly mammoth ( Mammuthus primigenius), and caribou ( Rangifer tarandus) – signature species of the Mammoth Steppe fauna ( Fig. 1), which was widespread from the British Isles, through northern Europe, and Siberia to Alaska, Yukon and adjacent Northwest Territories. The Yukon faunas extend from Herschel Island in the north to Revenue Creek in the south and from the Alaskan border in the west to Ketza River in the east. The Yukon holds evidence of the earliest-known people in North America. Artifacts made from bison, mammoth and caribou bones from Bluefish Caves, Old Crow Basin and Dawson City areas show that people had a substantial knowledge of making and using bone tools at least by 25 000 BP, and possibly as early as 40 000 BP. A suggested chronological sequence of Yukon Pleistocene vertebrates ( Table 1) facilitates comparison of selected faunas and indicates the known duration of various taxa.

Dental Characteristics of Late Pleistocene Equus Lambei from the Bluefish Caves, Yukon Territory, and their Comparison with Eurasian Horses

Bluefish Caves I, II and III of northern Yukon, have yielded the earliest in situ evidence of human occupation of Eastern Beringia, associated with one of the largest and most diverse Late Pleistocene faunas recovered in the region. This paper presents data derived from the study of a large sample of horse teeth recovered from the three caves. This research contributes to our knowledge of the Late Pleistocene Beringian equid, Equus lambei. A comparison of the dentition of E. lambei with that of some contemporary European horses, indicates they have similar size cheekteeth. The hypothesis of a Late Pleistocene trend of size reduction in equids is considered in the light of this comparison.

Macrofossil and pollen evidence for full-glacial steppe within an ecological mosaic along the Bluefish River, eastern Beringia

Plant and insect macrofossil assemblages dating to the full-glacial (late Wisconsinan) are rare from eastern Beringia. Here we present an assemblage of fossil pollen, insect and plant macrofossils recovered from alluvium at the Bluefish Exposure, northern Yukon Territory. Nine AMS radiocarbon ages place these data between ca. 18,880–16,440 14C yr BP (22,313–19,597 cal. yr BP). These data indicate that xeric steppe, rich in bunchgrasses Poa and Elymus, Artemisia frigida and diverse forbs was interspersed within a mosaic of local vegetation types, including mid-rich fens, mesic graminoid meadows, steppe-tundra and herb-tundra. Macrofossils and minor pollen of tundra forbs suggest steppe-tundra plant associations within midslope elevations and discontinuous herb-tundra on high elevation uplands on exposed bedrock ridges. The composition and distribution of local vegetation was dependent on available moisture, drainage, aspect and elevation. Compositional and physiognomic similarities can be made with extrazonal steppe-dominated dry slopes and high elevation steppe-tundra ecotones in central Alaska and Yukon Territory. Our paleoecological data reflect environments inhabited by the diverse late Pleistocene Bluefish Caves fauna, including woolly mammoth, horse, steppe bison, and saiga antelope.

Human dispersal into interior Alaska: antecedent conditions, mode of colonization, and adaptations

In spite of more than a half-century of exploration, no definitive evidence has yet come to light for human occupation in eastern Beringia preceding 12,000 yr BP. The oldest dates — between 11,500 and 12,000 yr BP — are from sites in interior and northern Alaska. Archaeological sites dating to this time period, such as the Broken Mammoth site in the central Tanana River Valley, have yielded evidence of pioneer colonization by groups with relatively little knowledge of lithic resources. Three possibly older cave sites — Bluefish Caves, Lime Hills Caves, and Trail Creek Caves — have stratigraphic and taphonomic problems that are not easily resolved. No sites in the glaciated coastal zone of southern Alaska are Pleistocene in date, and numerous objections can be raised to the viability of the coastal migration hypothesis, particularly in the western Gulf of Alaska region. For northern and interior Alaska, the earliest colonization appears to have been a “push–pull” phenomenon, linked to the dissolution of the Bering Land Bridge through a combination of rising sea levels and ameliorating climate. The climate of the “Birch-Poplar” rise in the terminal Pleistocene may have forced the extinction of obligate grazers such as mammoth and horse, but it seems to have favored other taxa such as bison and elk, at least until 9000 yr BP. Faunal data from the Broken Mammoth site in the central Tanana valley, with good organic preservation, demonstrate the utilization of a wide diversity of taxa, including small game, waterfowl, and fish. Faunal and sedimentological data give slight support to a Younger Dryas reversal, but this was dwarfed by the mid-Holocene period of dry, windy conditions during which interior Alaska may have been largely abandoned.

Paleoethological Reconstruction and Taphonomy of <i>Equus lambei</i> from the Bluefish Caves, Yukon Territory, Canada

The Bluefish Caves, northern Yukon, Canada, have yielded evidence of pre-Holocene human occupation of eastern Beringia. The three caves at Bluefish contain a large and complex late Pleistocene fauna in situ. Our research on the mortality patterns and the paleoethology of Equus lambei (an extinct species of horse), a dominant component of the Bluefish assemblages, was based on the dental remains. Mortality profiles for Equus lambei indicate that predators were the likely primary agents of bone accumulation at Cave I, while Caves II and III appear to have accumulated bones through accidental or natural deaths, probably regularly monitored by humans and other predator/scavengers. Paleoethological reconstruction for E. lambei, supports the suggestion the Bluefish Basin was not a polar desert during the late Pleistocene. Finally, the use of tooth height/age tables to establish age profiles of fossil equid populations is demonstrated to be limited to establishing broad, relative age categories.

Paleoecological implications of Late Pleistocene and Holocene microtine rodents from the Bluefish Caves, northern Yukon Territory

Bluefish Caves 1, 2, and 3 have produced tens of thousands of vertebrate remains among which at least nine species of microtine rodents are represented: red-backed vole, Clethrionomys rutilus; collared lemming, Dicrostonyx torquatus; brown lemming, Lemmus sibiricus; singing vole, Microtus miurus; tundra vole, Microtus oeconomus; meadow vole, Microtus pennsylvanicus; yellow-cheeked or taiga vole, Microtus xanthognathus; muskrat, Ondatra zibethicus; and northern bog lemming, Synaptomys borealis. Late Pleistocene and Holocene components are clearly distinguishable from one another in each of the three caves, and each component can be subdivided within cave 1. This paper discusses (i) variations in taxonomic abundance through time and between site areas, (ii) contrasts in microhabitat between north-facing cave 1 and south-facing cave 2, and (iii) decreases in tooth size that may reflect a reduction in the length of the growing season. A general decrease in diversity is shown to involve increased dominance and decreased species richness and evenness. These changes are attributed to postglacial zonation of habitat.