Homestead Cave Research Articles

Where does the time go?: Mixing and the depth-dependent distribution of fossil ages

Knowing how time is distributed within a fossil record is fundamental to paleobiology. Many efforts to quantify temporal resolution have estimated rates of specimen decay from the frequency distribution of specimen ages in near-surface assemblages. The implicit assumption has been that the shape of these distributions is invariant with depth and thus decay-rate estimates reflect the temporal resolution of a fossil record’s deeper layers as well. Here we present a new model that predicts how age-frequency distribution shape will change with depth due to the interplay of burial, mixing, and decay. Unlike previous models, this model distinguishes the dimensions of time, specimen age, and depth, and predicts a right-to-left shift in age-frequency distribution skewness, and a decrease in kurtosis, with increasing stratigraphic depth. We find support for these predictions with the accelerator mass spectrometry 14C dating of 80 small mammal specimens spanning the Quaternary fossil record of Homestead Cave, Utah (United States). Our study indicates (1) that previous models overestimate rates of specimen decay, (2) that the acuity of ecological information captured in near-surface assemblages is higher than previously inferred, and (3) how time-averaging can alter the apparent dynamics of biodiversity over time. We thereby offer a new quantitative framework to account for time-averaging, to merge modern and paleontological archives, and to place ecological systems within the context of their past dynamics.

Paleoenvironmental implications of two relative indicator rodent taxa during the Pleistocene to Holocene transition in south‐eastern Washington state, USA

ABSTRACTLocal pollen data, diminution of body size of three ungulate species, and decreased mammalian richness and evenness all indicate grass decreased in abundance during the Pleistocene–Holocene transition (PHT) in eastern Washington state, USA. This paleoenvironmental history suggests that the abundance of remains of Microtus sp. should decrease as remains of Peromyscus maniculatus increase in abundance during the PHT. These two taxa have well‐known ecologies relative to one another. PHT sediments at the Marmes archeological site in south‐eastern Washington state are sorted into three chronologically sequent, isotaphonomic analytical units. Relative abundances of remains of Microtus sp. and P. maniculatus shift across the analytical units in the predicted manner whether raw abundances or rarified abundances are considered. These results suggest relative abundances of remains of Microtus sp. and P. maniculatus recovered from other sites may be used as relative indicators of paleohabitats. Their abundances at Homestead Cave, Utah, shift as predicted from the Late Pleistocene through the Early Holocene.

The Bonneville Estates Rockshelter rodent fauna and changes in Late Pleistocene–Middle Holocene climates and biogeography in the Northern Bonneville Basin, USA

Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,50014CyrBP (14,800calyrBP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 900014CBP (10,200calyrBP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene–early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 950014CyrBP (10,800calyrBP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.

Within-taxon morphological diversity in late-Quaternary Neotoma as a paleoenvironmental indicator, Bonneville Basin, Northwestern Utah, USA

Ecological data indicate that as the amount of precipitation in an arid areas increases, so too does mammalian taxonomic richness. This correspondence has been found in two late-Quaternary mammalian faunas from Utah, one from Homestead Cave in the Bonneville Basin. We use the remains of two species of woodrat ( Neotoma cinerea and Neotoma lepida) from Homestead Cave to test the hypothesis that as the amount of precipitation in an arid area increases, so too does morphological diversity within individual mammalian taxa. Morphological diversity is measured as corrected coefficients of variation and as richness of size classes of mandibular alveolar lengths. Coefficients of variation for N. cinerea are few and coincide with moisture history if temporally successive small samples are lumped together. More abundant coefficients of variation for N. lepida coincide only loosely with moisture history, likely because such coefficients measure dispersion but not necessarily other aspects of variation. Richness of size classes of N. lepida is high during the early and late Holocene when moisture was high, and lowest during the middle Holocene when climate was most arid.

Holocene Environmental Change, Artiodactyl Abundances, and Human Hunting Strategies in the Great Basin

Despite a deep Great Basin tradition of incorporating paleoenvironmental change within ecologically oriented analyses of past human lifeways, there has been little attention focused on Holocene variation in artiodactyl abundances and the human hunting strategies dependent upon them. Here, we draw upon recently generated paleontological evidence from Homestead Cave of the Bonneville Basin to document a late Holocene artiodactyl population increase. We then use the prey model of foraging theory to predict late Holocene increases in the hunting of artiodactyls, relative to lagomorphs. That prediction is then tested against several fine-grained archaeological records of hunting behavior in the Bonneville Basin, Hogup Cave and Camels Back Cave, and a variety of more coarse-grained faunal records from throughout the Great Basin. Close fits are found between the deductively derived prediction and the empirical records of hunting behavior: dramatic proportional increases in artiodactyl hunting occurred during the late Holocene. The results have far-reaching implications for our understanding of prehistoric human adaptations in the Great Basin.

Small-Mammal Data on Early and Middle Holocene Climates and Biotic Communities in the Bonneville Basin, USA

Archaeological investigations in Camels Back Cave, western Utah, recovered a series of small-mammal bone assemblages from stratified deposits dating between ca. 12,000 and 500 14C yr B.P. The cave's early Holocene fauna includes a number of species adapted to montane or mesic habitats containing grasses and/or sagebrush (e.g., Lepus townsendii, Marmota flaviventris, Reithrodontomys megalotis, and Brachylagus idahoensis) which suggest that the region was relatively cool and moist until after 8800 14C yr B.P. Between ca. 8600 and 8100 14C yr B.P. these mammals became locally extinct, taxonomic diversity declined, and there was an increase in species well-adapted to xeric, low-elevation habitats, including ground squirrels, Lepus californicus and Neotoma lepida. The early small-mammal record from Camels Back Cave is similar to the 11,300–6000 14C yr B.P. mammalian sequence from Homestead Cave, northwestern Utah, and provides corroborative data on Bonneville Basin paleoenvironments and mammalian responses to middle Holocene desertification.

BIOGEOGRAPHIC IMPLICATIONS OF RECENT LOW-ELEVATION RECOLONIZATION BYNEOTOMA CINEREAIN THE GREAT BASIN

Homestead Cave, a paleontological site located in a low-elevation arid setting in the northern Bonneville Basin of northcentral Utah, documents the local extinction of Neotoma cinerea during the Middle Holocene. N. cinerea is present there today, and the Homestead Cave record suggests that recolonization likely occurred sometime prior to 1,000 years ago. This history supports the view (forwarded by T. E. Lawlor) that cross-valley dispersal by mammals that generally are most abundant in cooler and moister (and therefore higher elevation) parts of the Great Basin is still occurring, showing that Brown's model of Great Basin montane mammalian biogeography is incorrect. These dispersal patterns suggest that conservation efforts directed toward montane mammals in the Great Basin must include low-elevation access corridors to mountain masses.

Terminal Pleistocene Fish Remains from Homestead Cave, Utah, and Implications for Fish Biogeography in the Bonneville Basin

Abstract Eleven fish species were identified from Homestead Cave, Utah. The remains, concentrated in the lowest stratum of the deposit, were accumulated by owls between approximately 11,200 and 10,100 14C yr B.P. and likely represent fish associated with the final die-off of the Lake Bonneville fauna. Four of the species (Salvelinus confluentus, Prosopium abyssicola, Catostomus discobolus, Richardsonius balteatus) represent their first records for Lake Bonneville. The S. confluentus premaxilla is the first Quaternary specimen record for the genus in the Great Basin and suggests a southern range extension during the Pleistocene. The C. discobolus specimens represent the first fossil records for the subgenus Pantosteus in the Great Basin; their presence in Lake Bonneville documents a Pleistocene connection between two presently disjunct populations. The hyomandibulars of Prosopium gemmifer are different from Recent specimens in a pattern suggesting Holocene introgression with Prosopium spilonotus. The lack ...

Fish Remains from Homestead Cave and Lake Levels of the Past 13,000 Years in the Bonneville Basin

A late Quaternary ichthyofauna from Homestead Cave, Utah, provides a new source of information on lake history in the Bonneville basin. The fish, represented by 11 freshwater species, were accumulated between ∼11,200 and ∼1000 14C yr B.P. by scavenging owls. The 87Sr/86Sr ratio of Lake Bonneville varied with its elevation; 87Sr/86Sr values of fish from the lowest stratum of the cave suggest they grew in a lake near the terminal Pleistocene Gilbert shoreline. In the lowest deposits, a decrease in fish size and an increase in species tolerant of higher salinities or temperatures suggest multiple die-offs associated with declining lake levels. An initial, catastrophic, post-Provo die-off occurred at 11,300–11,200 14C yr B.P. and was followed by at least one rebound or recolonization of fish populations, but fish were gone from Lake Bonneville sometime before ∼10,400 14C yr B.P. This evidence is inconsistent with previous inferences of a near desiccation of Lake Bonneville between 13,000 and 12,000 14C yr B.P. Peaks in Gila atraria frequencies in the upper strata suggest the Great Salt Lake had highstands at ∼3400 and ∼1000 14C yr B.P.

Mammalian responses to Middle Holocene climatic change in the Great Basin of the western United States

AbstractIn spite of decades of intense research directed toward understanding the climates and ecology of the Great Basin (western United States) during the past 10,000 years, the responses of mammals to the extreme aridity of the Middle Holocene (c. 8000–5000 years ago) in this region have been poorly understood. Using a well‐dated small mammal sequence from Homestead Cave, north‐central Utah, I show that the Middle Holocene small mammal faunas of this area underwent a decrease in species richness and evenness, driven largely by a series of local extinctions and near‐extinctions coupled with a dramatic increase in the abundance of taxa well‐adapted to xeric conditions. At the end of this period, some taxa that require relatively mesic habitats began to increase in abundance immediately, others did not rebound in abundance until several thousand years later, while still others have not returned at all. This suite of responses has been difficult to detect because climatic change at the beginning of the Middle Holocene was so much more substantial than that which occurred toward its end.