Taphonomic Research Articles

Sulfidation of nano-magnetite to pyrite: Implications for interpreting paleoenvironmental proxies and biosignature records in hydrothermal sulfide deposits

Nano-magnetite is a potential archive for biosignatures and paleoenvironmental proxies in hydrothermal systems. However, sulfidic diagenesis at hydrothermal conditions potentially drives the rapid transformation of magnetite to Fe sulfide minerals. The identity and characteristics of transformation products from these reactions are crucial for interpreting biosignature records and paleoenvironmental proxies associated with Fe minerals in sulfide deposits. To constrain the preservation and transformation of magnetite in hydrothermal sulfide habitats, we incubated synthetic nano-magnetite in anoxic artificial seawater at a sulfide:Fe ratio of 4:1 as well as at different pH (7, 10) and temperatures (20-80°C), and in presence or absence of added S0. Experimental products were analyzed by means of sequential Fe extraction, μ-X-ray diffraction (μ-XRD), Raman spectroscopy, and scanning electron microscopy (SEM). After 46 days, nano-magnetite was only detected at 20°C (pH ∼10). Fe(III)-containing mackinawite and greigite formed at pH ∼10 and ≥20°C. At pH ∼7 and 80°C, magnetite was transformed to pyrite within only 19 days, with faster rates in the presence of polysulfides, which formed from the sulfide-mediated reduction of Fe(III) and in the presence of S0. Our results demonstrate a potential taphonomic bias against nano-magnetite in sulfidic hydrothermal habitats and suggest that pyrite-associated paleoenvironmental proxies and biosignature records of Fe- and S-cycling microorganisms in hydrothermal deposits are affected by diagenetic fluid-mineral interactions.

Taphonomic analysis of the Rosario Mine (Valdeteja Formation, Bashkirian, NW Spain): evidence of tsunamis or cyclones

ABSTRACT This study presents the analysis of the taphonomical processes at the Rosario Mine (Valdeteja Formation, León). The studied beds are an ensemble of normal graded sequences comprised of rudstones and grainstones that pass upwards to packstones and finally to marls. The last sequence culminates in a 3 m thick bed of carbonaceous shales with coal balls. In the limestones there are evidences of breakage, resedimentation and even some reworking. The top of the packstones and the marls show hummocky cross stratification and abundant burrows. The fossils in the limestones represent an allochthonous assemblage, while the marls contain a mostly autochthonous assemblage, typical of a deep marine environment.These sequences were deposited in a deep area of a tropical carbonate platform in a foreland basin, and they resulted from mass flows triggered by large waves followed by quiet background environmental conditions. Tsunamis or cyclones could be the events originating these sequences. The characteristic of the deposit and the palaeogeographical framework have been examined to try to differentiate between these events. The climate and tectonic context during the sedimentation support both possibilities, while the deep environment and the amount of plant remains dragged to the sea seem more consistent with tsunamis.

Flourishing chancelloriids from the Cambrian Kaili Biota of South China

ABSTRACT Diverse chancelloriids from two sections of the Kaili Biota (Cambrian Wuliuan Stage) in Guizhou Province, China, are systematically described. A total of 25 complete individuals were collected from calcareous silty mudstones of the Cambrian Kaili Formation and are assigned to 3 genera and 6 species, including Archiasterella anchoriformis sp. nov., Chancelloria zhaoi sp. nov., C. eros, Allonnia erjiensis, Al. phrixothrix, and Al. sp. The new species Ar. anchoriformis with sclerites characterised by a large angle between two marginal-lateral rays and an obvious apical tuft represents the first unambiguous Archiasterella scleritome in South China. The C. zhaoi is dominated by a series of bilaterally symmetrical, rosette-like sclerites that composed of five or six lateral rays and a central ray. Moreover, based on a careful survey of the spatial-temporal distribution of chancelloriids (including both scleritome and isolated sclerite fossils) in South China, two flourishing ages, though may be related to preservational bias, of this metazoan group are recognised: 1) a significant diversification in the upper Stage 2 to Stage 3 and 2) a thriving in the Wuliuan Stage.

Pliocene hominins from East Turkana were associated with mesic environments in a semiarid basin

During the middle Pliocene (∼3.8–3.2 Ma), both Australopithecus afarensis and Kenyanthropus platyops are known from the Turkana Basin, but between 3.60 and 3.44 Ma, most hominin fossils are found on the west side of Lake Turkana. Here, we describe a new hominin locality (ET03-166/168, Area 129) from the east side of the lake, in the Lokochot Member of the Koobi Fora Formation (3.60–3.44 Ma). To reconstruct the paleoecology of the locality and its surroundings, we combine information from sedimentology, the relative abundance of associated mammalian fauna, phytoliths, and stable isotopes from plant wax biomarkers, pedogenic carbonates, and fossil tooth enamel. The combined evidence provides a detailed view of the local paleoenvironment occupied by these Pliocene hominins, where a biodiverse community of primates, including hominins, and other mammals inhabited humid, grassy woodlands in a fluvial floodplain setting. Between <3.596 and 3.44 Ma, increases in woody vegetation were, at times, associated with increases in arid-adapted grasses. This suggests that Pliocene vegetation included woody species that were resilient to periods of prolonged aridity, resembling vegetation structure in the Turkana Basin today, where arid-adapted woody plants are a significant component of the ecosystem. Pedogenic carbonates indicate more woody vegetation than other vegetation proxies, possibly due to differences in temporospatial scale and ecological biases in preservation that should be accounted for in future studies. These new hominin fossils and associated multiproxy paleoenvironmental indicators from a single locale through time suggest that early hominin species occupied a wide range of habitats, possibly including wetlands within semiarid landscapes. Local-scale paleoecological evidence from East Turkana supports regional evidence that middle Pliocene eastern Africa may have experienced large-scale, climate-driven periods of aridity. This information extends our understanding of hominin environments beyond the limits of simple wooded, grassy, or mosaic environmental descriptions.

Combining quantification, sex, age, and utility patterns to interpret two dugong bone mounds from Woeydhul Island (Western Torres Strait, Australia)

The analysis of dugong bone mounds in the Torres Strait Islands has traditionally focused on ritualized deposition and treatment of remains, the distinction between formalized ritual and midden refuse, and their socio-political and spiritual role within Torres Strait Islander seascapes. Research has consistently targeted the abundance of specific skeletal elements in a mound, with interpretations frequently based on the calculation of common quantitative units (i.e., NISP and MNI) or relative weight to assess proportional representation. Far less research has focused on the taphonomic history and processes embodied by these mounds. This paper presents a novel zooarchaeological and taphonomic analysis of dugong bone mounds where qualitative and quantitative data are combined. Through the analysis of two assemblages from Woeydhul Island (Western Torres Strait, Australia), this paper provides inferences regarding deposition time span and formalized depositional behaviors. Our research examines the age distribution of represented animals and differential butchery practices associated with anatomical provenance, while also suggesting new methods for identification of sex ratios in these assemblages. Our results provide new approaches to investigate dugong hunting by past Torres Strait communities, proposing the combination of sex, butchery patterns, and meat utility indices to interpret the meaning of dugong bone mounds in the Western Torres Strait.

New records of dinosaur tracks in eastern Tibet and a review of Middle Jurassic dinosaur faunas from the eastern Tethys, southwest China

ABSTRACT We report five new dinosaur track sites in Chaya County, about 120 km southeast of Changdu City. The track assemblages are dominated by sauropods (45 tracks), which have been identified tentatively as cf. Brontopodus. Also present are two thyreophoran trackways consisting of 13 tracks that show strong similarities with the ichnogenus Deltapodus, the potential trackmakers of which were probably stegosaurids. The sauropod tracks from the Chaya region are dominated by large tracks with different affinities if compared to those of the Changdu area. The isolated sauropod tracks from Changdu and Chaya regions show similar morphological patterns, but those from the Chaya region lack large scale tracks. This paper compares and discusses the known ichno and body fossil records of sauropods, theropods, and ornithischians from the Middle Jurassic of Yunnan, Sichuan, and eastern Tibet and their importance for our understanding of dinosaur faunas from this region. The absence of basal neornithischian records in the Yunnan and Changdu regions is likely a preservational bias but also an ecological pecularity cannot be completely excluded. The palaeogeographic position of the four sampled skeleton and track sites suggests the possible existence of a corridor through which faunal exchanges were taking place throughout the Jurassic.

The signature of the stones: pXRF studies on prehistoric axes from the Eastern Sahara

Prehistoric stone axes are common in the Sahara but not much attention has been paid to them in recent research. Necked axes, also “haches à gorge” or “Darfur axes”, are a remarkable form of axes, which are characterised by a groove and a round or mushroom shaped neck. This rather peculiar type is widespread throughout the Sahara and can be linked with different pastoral groups of the 5th to 3rd/2nd millennia BCE. The distribution of these axes between the Nile Valley and Mali raises questions of trade and transport. In this regard the raw material used for the manufacture of these axes is of special interest. Visual rock determination of necked axes from the eastern Sahara, especially from the Wadi Howar and Laqiya regions in northern Sudan, indicates igneous rocks, mainly diabase, as raw material. As macroscopic raw material determination of archaeological objects can be difficult due to ancient surface treatment and taphonomic processes, a non-destructive elemental analysis approach was performed. pXRF analysis carried out on 62 pieces from the eastern Sahara for the first time allowed to further distinguish different rock groups based on their chemical composition. Comparison between pXRF measurements on the natural and fresh surfaces was made to address the question of taphonomic influence. A look for potential raw material sources for the production of the necked axes found in northern Sudan indicate a regional provenance of the raw material to be probable.

Paleolakes and socioecological implications of last glacial “greening” of the South African interior

Determining the timing and drivers of Pleistocene hydrological change in the interior of South Africa is critical for testing hypotheses regarding the presence, dynamics, and resilience of human populations. Combining geological data and physically based distributed hydrological modeling, we demonstrate the presence of large paleolakes in South Africa's central interior during the last glacial period, and infer a regional-scale invigoration of hydrological networks, particularly during marine isotope stages 3 and 2, most notably 55 to 39ka and 34 to 31ka. The resulting hydrological reconstructions further permit investigation of regional floral and fauna responses using a modern analog approach. These suggest that the climate change required to sustain these water bodies would have replaced xeric shrubland with more productive, eutrophic grassland or higher grass-cover vegetation, capable of supporting a substantial increase in ungulate diversity and biomass. The existence of such resource-rich landscapes for protracted phases within the last glacial period likely exerted a recurrent draw on human societies, evidenced by extensive pan-side artifact assemblages. Thus, rather than representing a perennially uninhabited hinterland, the central interior's underrepresentation in late Pleistocene archeological narratives likely reflects taphonomic biases stemming from a dearth of rockshelters and regional geomorphic controls. These findings suggest that South Africa's central interior experienced greater climatic, ecological, and cultural dynamism than previously appreciated and potential to host human populations whose archaeological signatures deserve systematic investigation.

An assessment of whether saturated sediment ablation on stationary bone can mimic bone tool use-wear from Earlier Stone Age contexts

Several taphonomic processes can alter the surface of archaeological bone in a manner that may cause them to superficially resemble bone tools used as digging implements. Under close examination, however, the resultant microwear is usually quite distinct. While many experiments have been done to document the effects of fluvial processes on bone surface alteration, there are many mass soil movement process whose microwear effects have not yet been properly investigated and which could conceivably produce microwear similar to digging implements. One example, which pertains to the Cradle of Humankind landscape, is soil creep. We present the results of an experiment that assesses the resultant microwear on stationary bones occasioned by artificially accelerated soil creep processes. We show that the passage of saturated sediments over stationary bones produces rounding and pitting, and does not resemble microwear occasioned either by fluvial transport or experimental digging in sediments. Although there is room to test additional variables, we conclude that the purported bone tools from the Cradle of Humankind sites were not affected by soil creep processes, at least not to the extent that they caused surface alterations.

Decoding the drivers of deep‐time wetland biodiversity: insights from an early Permian tropical lake ecosystem

AbstractWetlands are important to continental evolution, providing both arenas and refugia for emerging and declining biotas. This significance and the high preservation potential make the resulting fossiliferous deposits essential for our understanding of past and future biodiversity. We reconstruct the trophic structure and age of the early Permian Manebach Lake ecosystem, Germany, a thriving wetland at a time when the tropical biosphere faced profound upheaval in the peaking Late Palaeozoic Icehouse. Nine excavations, high‐resolution spatiotemporal documentation of fossils and strata, and U–Pb radioisotopic dating of tuffs allow us to distinguish autogenic and allogenic factors shaping the limnic biocoenosis. The Manebach Lake was an exorheic, oxygen‐stratified, perennial water body on the 101–102 km2 scale, integrated into the catchment draining much of the European Variscides. Lake formation paralleled an Asselian regional wet climatic interval and benefited from rising base level due to post‐Variscan half‐graben tectonics. Stromatolite‐forming cyanobacteria, bivalves, several crustaceans, amblypterids and xenacanthid sharks formed a differentiated biocoenosis in the lake. Fossil stomach remains and teeth prove the rare presence of acanthodians, branchiosaurs and large amphibians. The results indicate woody‐debris‐bearing lake littorals devoid of semi‐aquatic and aquatic plants as places suitable for stromatolites to grow, underpin the model of declining freshwater‐shark diversity in most Permian Variscan basins, demonstrate fish/amphibian ratios in limnic assemblages to measure lake perenniality and reveal taphonomic biases in lake taphocoenoses. Our outcomes call for more knowledge about the diversity, ecology and fossilization pathways of past limnic biotas, particularly microorganisms and actinopterygian fishes, to reconstruct deep‐time continental ecosystems.

The Potential of Palynology with Regard to the Archaeology of Medieval Monastery Sites in Iceland

In 2014, as part of the Kortlagning klaustur á Íslandi (Mapping Monasticism in Iceland) archaeological project, bulk samples retrieved from various archaeological sites associated with Icelandic monasticism were subsampled for pollen analysis. The objective was to discern something about the character of the past vegetation that surrounded the sites under archaeological investigation as well as to detect the presence of exotic pollen derived from plant species with medicinal, culinary, and other utilities. Two methods were applied: a standard pollen count (up to 300 pollen grains) and rapid scanning (where all pollen were examined but only exotics were recorded). The pollen surveys showed mixed results in achieving the intended insights, mostly due to taphonomic processes (wind and depositional environments), exacerbated by poor chronological resolution. However, there was sufficient data to suggest that careful selection and analysis of subsamples from archaeological contexts can allow some reconstruction of past vegetation communities and land use practices. The presence of cereal type pollen might suggest cultivation and/or storage of grain in association with medieval archaeological contexts. Furthermore, palynology was able to discern some evidence of the importation of plants for medicinal purposes to Iceland.

What can be gained from studying coprolite taphonomy: the case of Villanueva-1 (Palencia, Spain)

ABSTRACT Coprolites are relatively common trace fossils in Quaternary sites and are used to obtain a variety of information that goes from environment reconstruction to dating sites or recovering DNA among others. However, little attention is given to taphonomic processes undergone by the coprolites that might compromise their validity as sources of information. In this paper, we present the study of the Middle Pleistocene coprolites of Villanueva-1 from a taphonomic point of view and discuss the results of the analyses performed and how the taphonomic alterations identified have an effect on palaeoecological interpretations based on these fossils. Modifications prior to burial may be determined by direct observation of shape, colour, fractures and inclusions. Some diagenetic alterations can also be inferred from colour differences, but mostly require destructive analyses in order to identify the degree of chemical and structural changes that might interfere with content preservation, such as pollen, DNA, or organic carbon for dating purposes.

Tracing microbial communities associated with archaeological human samples in Latvia, 7-11th centuries AD.

In the grave environment, microorganisms are major ecological participants in the successional decomposition of vertebrates and could infiltrate the skeleton/skeletal material during taphonomic processes. The diversity of archaeological skeleton-associated microbial assemblages and the impact of various factors are poorly understood. This study aimed to evaluate the taxonomic microbial composition of archaeological human bone and teeth samples from the 7th to 11th centuries AD from two burial sites in Latvia. Samples were analysed by a shotgun metagenomics-based approach. The results showed a strong presence of the environmental DNA in the samples, and variability in microbial community structure between individual samples. Differences in microbial composition were observed between bone and tooth samples, as well as between different burial sites. Furthermore, the presence of endogenous ancient DNA (aDNA) in tooth samples was detected. Overall, compositions of microbial communities associated with archaeological human remains in Latvia dated 7-11th century AD were influenced by the sample type and burial location. These findings indicate that, while the content of historical DNA in archaeological samples is low, the comparison of archaeological skeleton-associated microbial assemblages across time and space, along with aDNA damage profile analysis, is important and could help to reveal putative ancient microorganisms.

Morphological and organic spectroscopic studies of a 44-million-year-old leaf beetle (Coleoptera: Chrysomelidae) in amber with endogenous remains of chitin

This study details the quality of preservation of amber deposits in the Eocene. Through Baltic amber crack-out studies using Synchrotron Micro-Computed Tomography and Scanning Electron Microscopy it was found that the cuticle of a specimen of leaf beetle (Crepidodera tertiotertiaria (Alticini: Galerucinae: Chrysomelidae)) is exceptionally well preserved. Spectroscopic analysis using Synchrotron Fourier Transform Infrared Spectroscopy suggests presence of degraded upalpha-chitin in multiple areas of the cuticle, and Energy Dispersive Spectroscopy supports the presence of organic preservation. This remarkable preservation is likely the result of several factors such as the favourable antimicrobial and physical shielding properties of Baltic amber as compared to other depositional media, coupled to rapid dehydration of the beetle early in its taphonomic process. We provide evidence that crack-out studies of amber inclusions, although inherently destructive of fossils, are an underutilised method for probing exceptional preservation in deep time.

On the Sadler Effect and biases in Holocene paleofire records

Relationships between rates of change in Earth-surface systems and their measurement durations suggest that rates may be critically dependent on durations of observation. Studies relating rates and durations of change have appeared increasingly over the past 50 years, with many specifically discussing the importance of the ‘Sadler Effect’, the observation that plots of log duration versus log rate commonly define trends with slopes approaching minus unity toward shorter durations. Concurrently, paleofire research focusing on sedimentary charcoal in lakes has exhibited a similar profusion, with recent paleofire studies noting that both sedimentation rates as well as charcoal accumulation rates share a negative power law relationship with the time span of their measurement, suggesting longer time spans may be inherently biased toward lower charcoal fluxes because of the greater incorporation of sedimentary hiatuses over longer time intervals of measurement.Here we examine the premise that paleofire lake records might exhibit systematic biases because of the greater temporal completeness of younger successions. We evaluate the importance of preservation biases through examination of Holocene increases of sediment deposition and charcoal accumulation rates in 14 Alaskan lakes, and conclude that observed negative trends apparent in log duration versus log rate plots are a result of time as a variable in both axes (duration and rate). However, such self-correlation does not preclude the possibility of a systematic incorporation of sedimentary hiatuses in older portions of these sedimentary records. Age-dating and modelling techniques employed in paleofire research do not allow us to decide if these patterns stem from purely ‘Sadlerian’ preservation bias. Regardless, dependencies of process rate on process duration in these, as well as other, sedimentary archives have the potential to impact paleofire interpretations. Disentangling the drivers and biases inherent to paleofire archives is especially important due to climate change and the increasing need to establish paleofire baselines.

SALINITY-RELATED PRESERVATION OF MOLLUSKS IN SHALLOW LAKES: IMPLICATIONS FOR THE UNDERSTANDING OF THE LACUSTRINE PAMPEAN FOSSIL RECORD

ABSTRACT Premortem and postmortem processes significantly influence the formation of the molluscan fossil record in freshwater environments. Despite their importance for paleoenvironmental studies, they remain poorly understood. In Pampean shallow lakes, Holocene shell deposits of the euryhaline snail Heleobia parchappii show a relation with salinity, as preservation seems to be favored by brackish-saline water conditions. To explore if this pattern may respond to ecological (i.e., differential survival and reproduction) or taphonomic processes acting differently in freshwater and brackish-saline environments, we conducted a field-based study comparing premortem (abundance, length, width/length ratio, and crushing resistance in living and dead shells) and postmortem (fragmentation, fine-scale surface alteration, and loss of periostracum of dead shells) attributes along a modern lacustrine salinity gradient (0.5–40 ppt) in the Pampa plain of Argentina. Snails from saline lakes were smaller and more rotund than those from freshwater lakes, exhibiting higher abundances and resistances in death assemblages. They showed the highest fidelity in shell length and the best states of preservation, which were similar to values recorded in fossil shells. We concluded that shells deposited in saline lakes are better preserved than those deposited in freshwater lakes, giving rise to highly abundant shell concentrations, analogues to those shell-rich fossil levels recorded in Pampean lakes. Such abundance does not reflect the natural abundances of living snails, but rather is the result of the combined influence that less destructive environments and better shell intrinsic properties have on preservation.

Paleoparasitological study of avian trace fossils from the Tremembé Formation (Oligocene of the Taubaté Basin), São Paulo, Brazil

Coprolites are promising tools for the understanding of paleoecological and paleoenvironmental aspects. Through its chemical composition and analysis of micro- and macrostructures, it is possible to obtain information about the diet of ancient animals and insights into the climate and vegetation of paleoenvironments. Paleoparasitological analysis of these trace fossils help to understand the parasite-host relationship and how parasitic infections were processed in the past. The present study aims to identify helminths in coprolites of the Tremembé Formation (Oligocene of the Taubaté Basin, São Paulo). Furthermore, we included the descriptive association of the paleoparasitological data with the paleoenvironmental information present in the literature for this geological formation. Eggs were identified through linear morphometry and morphology. The paleoparasitological analysis revealed the presence of Nematode eggs of Ascaridina, Spirurina, and Trichocephalida, with a prevalence of 5% for each group. The complex life cycle of some nematodes would be made possible by the wide faunal diversity of birds, fish, and arthropods that inhabited the Tremembé paleolake. The low prevalence of helminths in the samples may be related to taphonomic processes. This study represents the first paleoparasitological analysis of avian coprolites from the Tremembé Formation. In addition, the finding of these helminth records creates new perspectives for the studies of this geological unit through the epidemiological point of view associated with the local paleofauna and also provides new subsidies for the further development of evolutionary and biogeographic helminth studies.

Parsing prehistoric patterns: Prospects and limitations of a big radiocarbon dataset for understanding the impact of climate on Late Palaeolithic and Mesolithic populations in northwest Europe (16–7.5 ka calBP)

Hunter-gatherer populations in northwest Europe were variably affected by Late Glacial and Early Holocene climate fluctuations and their effects on sea level and the environment. We investigate the impact of these fluctuations with a dates-as-data approach to a large radiocarbon dataset. Radiocarbon dates are used as a proxy for past human activity, the intensity, nature and archaeological visibility of which will indirectly influence date density. The significance of changes is explored using Kernel Density Estimates and model tested Summed Probability Distributions. Whereas previous studies have focused on smaller highly curated datasets to minimise research and preservation biases, our more inclusive approach maximises sample size, which is essential for these methods to reliably reflect underlying patterns. To deal with biases, we test subsets of the dataset that are potentially affected by differences in formation processes.The summed radiocarbon dataset follows the general fluctuations of climate conditions, showing increased activity in temperate periods and decreased activity during cold phases. Our results indicate significant periods of interest where the data deviates positively or negatively from our models. Notably we observe the impact of the Younger Dryas, Preboreal Oscillation and the 8.2 ka event on the density of hunter-gatherer activity. Additionally we see peaks in activity in our dataset during the Early and Late Boreal. Permutation testing of different regions in the research area shows these patterns are geographically differentiated.Our exploration of biasing factors indicates that we should be careful to interpret the abovementioned patterns, as different sampling processes and national policies may lie at the basis of several patterns. Furthermore, calibration artefacts may also cause issues at key parts of the timeline. Dates-as-data approaches require an understanding of the archaeology, the timing of external events, the impact of the calibration curve and how biases inherent to the dataset and research area may have influenced the formation of patterns in the result.

Differentiating taphonomic features from trampling and dietary microwear, an experimental approach

ABSTRACT Dental microwear is a common and wellestablished technique which allows the short-term reconstruction of the dietary behaviour in extinct and extant vertebrates, allowing inferences about daily, seasonal, or regional variations in diets. However, the use of this method may be limited because taphonomic processes can affect enamel surfaces and modify or obliterate dietary microwear features. Considering the substantial number of agents which can impact the archaeological record, dental microwear alteration processes are poorly known, producing a potential bias in dietary interpretations. In this study, the effect of trampling on dental occlusal surfaces, one of the most common processes recorded in archaeological assemblages, has been experimentally investigated for the first time. The results allowed us to (1) distinguish taphonomic and dietary marks; (2) assess the impacts of trampling on occlusal surfaces; and (3) infer the agents which modified the dental microwear from the teeth obtained from the archaeological sites. The importance of this work lies in the specific guidelines it offers to discriminate trampling marks from microwear features, improving the reliability of dietary interpretations.

Bothersome burrowers: Tracking the impact of Botta’s pocket gopher (Thomomys bottae) bioturbation on a late-Holocene site

Archaeological and paleontological research relies on the contextualization of artifacts and skeletal remains, but stratigraphic disturbances such as bioturbation can complicate temporal associations. More specifically, the mixing of fossil and subfossil material by pocket gophers (Thomomys spp.) may increase time-averaging, obscuring or even erasing stratification in terrestrial, open-air sites. Not only can bones be transported vertically by displacement of dirt by pocket gophers, but also the gophers themselves may die in their burrows, adding young skeletal remains to older deposits. Using a late-Holocene archaeological site in California as a case study, we establish the degree of bias introduced by native pocket gophers, Thomomys bottae, by radiocarbon-dating incisors of T. bottae and non-gopher small mammals from the same stratigraphic units. The ages of T. bottae incisors are younger overall, and span a wider age range, than the ages of other small mammals from the same sediment layers. Our data shows that a significant number of pocket gopher remains were introduced after the site’s deposition, and we conclude that this is a consequence of T. bottae burrowing. These results shed light on a common taphonomic process and may prompt reevaluation of faunal community reconstructions from fossil deposits impacted by pocket gophers and other fossorial mammals around the world.