Mark Clementz | University of Wyoming (original) (raw)

Papers by Mark Clementz

Quaternary Research

Limited numbers of high-resolution records predate the Last Glacial Maximum (LGM) making it diffi... more Limited numbers of high-resolution records predate the Last Glacial Maximum (LGM) making it difficult to quantify the impacts of environmental changes prior to peak glaciation. We examined sediments from Last Canyon Cave in the Pryor Mountains of Montana and Wyoming to construct a >45 ka environmental record from pollen and stable isotope analysis. Artemisia pollen was hyper-abundant at the beginning of the record. Carbon isotope values of bulk organic matter (>40 ka) showed little variation (-25.3 ± 0.4‰) and were consistent with a arid C3 environment, similar to today. After 40 cal ka BP, Artemisia pollen decreased as herbaceous taxa increased toward the LGM. A significant decrease in δ13C values from 40–30 cal ka BP (~1.0‰) established a new baseline (-26.6 ± 0.2‰), suggesting cooler, seasonally wetter conditions prior to the LGM. These conditions persisted until variation in δ13C values increased significantly with post-glacial warming, marked by two spikes in values at 14...

Geology

Interactions between midlatitude westerlies and the Pamir–Tian Shan mountains significantly impac... more Interactions between midlatitude westerlies and the Pamir–Tian Shan mountains significantly impact hydroclimate patterns in Central Asia today, and they played an important role in driving Asian aridification during the Cenozoic. We show that distinct west-east hydroclimate differences were established over Central Asia during the late Oligocene (ca. 25 Ma), as recorded by stable oxygen isotopic values of soil carbonates. Our climate simulations show that these differences are present when relief of the Pamir–Tian Shan is higher than 75% of modern elevation (∼3000 m). Integrated with geological evidence, we suggest that a significant portion of the Pamir–Tian Shan orogen had reached elevations of ∼3 km and acted as a moisture barrier for the westerlies since ca. 25 Ma.

Proceedings of the National Academy of Sciences

Near-modern ecosystems were established as a result of rapid ecological adaptation and climate ch... more Near-modern ecosystems were established as a result of rapid ecological adaptation and climate change in the Late Miocene. On land, Late Miocene aridification spread in tandem with expansion of open habitats including C4 grassland ecosystems. Proxy records for the central Andes spanning the Late Miocene cooling (LMC) show the reorganization of subtropical ecosystems and hydroclimate in South America between 15 and 35°S. Continental pedogenic carbonates preserved in Neogene basins record a general increase of δ18O and δ13C values from pre-LMC to post-LMC, most robustly occurring in the subtropics (25 to 30°S), suggesting aridification and a shift toward a more C4-plant-dominated ecosystem. These changes are closely tied to the enhancement of the Hadley circulation and moisture divergence away from the subtropics toward the Intertropical Convergence Zone as revealed by climate model simulations with prescribed sea-surface temperatures (SSTs) reflecting different magnitudes of LMC stee...

Royal Society open science, 2017

High-elevation environments above 2500 metres above sea level (m.a.s.l.) were among the planet&#3... more High-elevation environments above 2500 metres above sea level (m.a.s.l.) were among the planet's last frontiers of human colonization. Research on the speed and tempo of this colonization process is active and holds implications for understanding rates of genetic, physiological and cultural adaptation in our species. Permanent occupation of high-elevation environments in the Andes Mountains of South America tentatively began with hunter-gatherers around 9 ka according to current archaeological estimates, though the timing is currently debated. Recent observations on the archaeological site of Soro Mik'aya Patjxa (8.0-6.5 ka), located at 3800 m.a.s.l. in the Andean Altiplano, offer an opportunity to independently test hypotheses for early permanent use of the region. This study observes low oxygen (δ(18)O) and high carbon (δ(13)C) isotope values in human bone, long travel distances to low-elevation zones, variable age and sex structure in the human population and an absence o...

ABSTRACT Seagrasses are highly productive components of coastal ecosystems that play significant ... more ABSTRACT Seagrasses are highly productive components of coastal ecosystems that play significant roles in the flow of nutrients and the modulation of physical conditions within the world's oceans. However, in spite of the significant role seagrasses play today, the fossil record contains little evidence of the distribution and abundance of seagrass species in the past and many questions about their biology, ecology, and evolutionary history remain. We have developed, and present here, a parameter driven numerical model of global seagrass biogeography and diversity appropriate for paleontological and paleoecological investigations. The global distribution of seagrasses in our model is dependent on four input parameters, water temperature, water salinity, water depth, and photosynthetically available radiation at depth. With these limited inputs, our model captures both the location and biodiversity of modern seagrass distributions well. The simplicity of our model and its robust representation of modern conditions give it tremendous flexibility for applications throughout the ~70 Ma long history of seagrasses. Paleo ocean temperatures, salinity, water depths, and incident radiation are available from paleoclimatic/proxy datasets and/or numerical simulations of past environmental/climatic conditions, thus permitting investigations into time specific seagrass biogeography and diversity throughout its evolutionary history. In addition, the simplicity of our model allows for theoretical investigations of seagrass paleoecology and response to environmental changes. Both applications will contribute significantly to furthering our understanding of seagrasses, seagrass dominated ecosystems, and the roles they have played in the earth system over the past 70 Ma.

Science China Earth Sciences, 2016

Paleobiology, Mar 20, 2004

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Journal of evolutionary biology, Jan 5, 2015

The development of pierce-feeding and loss of oral processing represented major adaptations for u... more The development of pierce-feeding and loss of oral processing represented major adaptations for underwater feeding in marine mammals. We examined the evolution of pierce-feeding and its association with changes in tooth spacing and tooth size to determine whether pierce-feeding was practiced by the earliest known pinnipeds. Data on crown size and spacing in postcanine dentition were collected and 1) analyzed by principal components analysis (PCA) to determine the tooth morphospace of arctoid carnivores, 2) analyzed by least squares (LS) regression and phylogenetic independent contrasts (PIC) to determine what morphological variables were associated with increases in tooth spacing, and 3) used to reconstruct the evolution of feeding related traits within a phylogenetic context. The PCA analysis revealed that within arctoid carnivores the greatest differences in morphospace were associated with pierce-feeding, and the early-diverging seal Enaliarctos was placed within the pinniped mor...

Abstracts With Programs Geological Society of America, 2009

Increased nutrient loading via both natural and anthropogenic factors has been reported as one po... more Increased nutrient loading via both natural and anthropogenic factors has been reported as one possible mechanism for the recent increase in the occurrence and intensity of harmful algal blooms (HAB) in coastal ecosystems. Influx of iron, phosphorous, and organic carbon have proven to be significant stimulating factors for HAB, since the benthic cyanobacteria that often make up these blooms are capable of nitrogen-fixation and require these nutrients for this process as well as photosynthesis. These cyanobacteria can switch to direct uptake of dissolved inorganic nitrogen (DIN), however, when concentrations are high enough to energetically favor this source, suggesting that high nitrogen input may also stimulate HAB. Given the distinct isotope differences between atmospheric N2 (00/00) and anthropogenic sources of DIN (>60/00), measurement of the delta15N composition of cyanobacteria can provide a means of gauging the relative significance of anthropogenic versus atmospheric nitrogen to the growth of these blooms. Likewise, the delta13C composition of these primary producers is controlled by the delta13C composition of the DIC, and can be a second tracer of anthropogenic influx into marine ecosystems. A combined approach using both isotope tracers was employed to determine the significance of anthropogenic nitrogen on HAB in subtropical/tropical coastal marine ecosystems. Samples of cyanobacteria and associated macroalgae were collected from three coastal sites in Guam (Facpi Point, Tanguisson, and Ypao Beach), one locality in Hawaii, and three sites in southern Florida (Pepper Park, Fort Lauderdale, Florida Keys). Following removal of marine carbonates via an acid rinse, the delta13C and delta15N values were determined for each species. Cyanobacterial delta15N values ranged from -2.30/00 to 7.70/00 with the highest values reported from sites in Guam. Only cyanobacteria sampled from Hawaii showed no isotope evidence of an anthropogenic source for nitrogen. A strong negative correlation between delta13C and delta15N values was detected for cyanobacteria from all sites. This correlation suggests that cyanobacteria are fixing nitrogen under oligotrophic conditions, but switch to using the readily available DIN when the nutrient load is high. The discovery of this relationship in three separate locations and among several different species of cyanobacteria suggests that this is a common feature of HAB and that nitrogen influx may have a more significant impact on the formation of these blooms than previously thought.

Paleobiology

Dental morphology changes dramatically across the artiodactyl-cetacean transition, and it is gene... more Dental morphology changes dramatically across the artiodactyl-cetacean transition, and it is generally assumed that this reflects the evolutionary change from herbivory and omnivory to carnivory. To test hypotheses regarding tooth function and diet, we studied size and position of wear facets on the lower molars and the stable isotopes of enamel samples. We found that nearly all investigated Eocene cetaceans had dental wear different from typical wear in ungulates and isotope values indicating that they hunted similar prey and processed it similarly. The only exception is the protocetid Babiacetus, which probably ate larger prey with harder skeletons. The closest relative of cetaceans, the raoellid artiodactyl Indohyus, had wear facets that resemble those of Eocene cetaceans more than they do facets of basal artiodactyls. This is in spite of Indohyus's tooth crown morphology, which is unlike that of cetaceans, and its herbivorous diet, as indicated by stable isotopes. This impli...

Sedimentary basins straddling the margin of the Puna Plateau in northwest Argentina constitute an... more Sedimentary basins straddling the margin of the Puna Plateau in northwest Argentina constitute an important archive of tectonic and paleogeographic information. The Angastaco basin is the largest Cenozoic sedimentary basin in the Eastern Cordillera and preserves a continuous record of ~6 km of alluvial and lacustrine sedimentation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system that migrated through the region from late Eocene through middle Miocene time. Detrital zircon U-Pb ages provide an Eocene (~38 Ma) maximum depositional age for the oldest unit in the succession, the Quebrada de los Colorados Formation, which is interpreted as distal to proximal foredeep deposits. Development of an angular unconformity at ~14 Ma and the coarse-grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge-top depozone. Deposition of the Palo Pint...

Journal of Paleontology

sees sustainable scholarly publishing as an inherently collaborative enterprise connecting author... more sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne's Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. ABSTRACT—The early Miocene site of Wadi Moghra, Qa...

Earth and Planetary Science Letters, 2015