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The Eocene Green River Formation (GRF) (United States) is one of the best-known and most extensively studied Konservat Lagerstätte in the world. As most studies have focused on the fossil fish and plants, few studies have examined the invertebrates, particularly the ostracodes of the renowned GRF fauna. Six species of ostracodes were recovered from 18 intervals within a 154 m section of the Laney Member (LM) in the Washakie Basin (WB). Ostracode species recovered occupied a variety of biological niches, including plant and mud dwellers as well as nektonic lifestyles. Ecological tolerances of these ostracodes were used to reconstruct environmental conditions of the lake through this portion of its history. The taphonomic mode of the ostracodes varied with lithology and depositional setting. Diversity analyses show that the ostracodes from the lower and upper Laclede beds of the LM are consistent with the lake-level fluctuation model constructed for the WB, which was based on independent, stratigraphic, isotopic, and sedimentological data. Ostracode response to changing lake conditions within the LM demonstrates an environmental tracking (i.e., coordinated stasis) of the lake-level variation. In addition, the similarity of ostracode faunas between the LM and those reported from the Uinta Basin (UB) supports the possible paleohydrologic connection of various basins with deposits of the GRF, related to the tectonic uplift and concomitant climatic change during the Paleocene-Eocene Thermal Maximum. The establishment of these paleohydrologic connections provides important constraints pertaining to the tectonic and climatic history of this region.
The late Campanian–Maastrichtian Liscomb Bonebed is the richest source of dinosaur remains thus far documented in the polar regions. This bed is formally defined herein and assigned to the upper part of the Prince Creek Formation; the bonebed and several other organic-rich beds are part of a 178 m sequence of fluvial and volcaniclastic deposits. The Liscomb Bonebed is a mudstone rich in clay, comminuted plant remains, and palynomorphs with a total organic carbon (TOC) of 6.80%–10.55%. It contains a multitaxic, low-diversity, dinosaur assemblage, dominated by Edmontosaurus sp., which is primarily represented by late juveniles. Four theropod taxa are almost exclusively represented by isolated teeth. With >6000 specimens collected, the assemblage is characterized by a Minimum Number of Individuals (MNI) of 36, dominance of Voorhies Groups I and II, and an underrepresentation of teeth, skulls, and girdles. Bones are highly fragmented and exhibit low weathering and abrasion indices. Bite marks occur on slightly more than 1% of elements. The densest accumulations of bone are typically found in the middle third of the bed with the largest bones at the bottom. The Liscomb Bonebed assemblage resulted from mass mortality associated with overbank floods that formed floodplain mires and ponds. Data from the current study clearly establish the Alaskan Arctic as the year-round residence of a rich dinosaur fauna and add further support to the hypotheses that even high-latitude hadrosaurids were gregarious and formed social groups.
Dinosaurs, like modern birds, produced enormous quantities of eggshell as part of the reproductive process. Sometimes this eggshell was fossilized but most commonly was destroyed by weathering. The degree to which bacteria may have contributed to this weathering process has not been explored. In this study, fresh glaucous-winged gull (Larus glaucescens) eggshell fragments were collected from the surface of a breeding colony in Washington, sterilized, and buried in sterile soil. The soil surrounding replicate experimental fragments was inoculated with a culture of one of five species of soil bacteria isolated from other eggshell fragments collected on the colony surface. Replicate control fragments received the same treatment minus the bacteria. Weekly changes in protein concentration and fragment mass, as well as in soil pH and calcium concentration, were measured for experimental and control fragments over 10 weeks. The presence of all five types of bacteria degraded the eggshell and produced corrosion patterns similar to those seen in naturally weathered eggshell. On the basis of the results we postulate that bacterial decomposition of the eggshell protein matrix produces organic acids, which, in turn, dissolve the CaCO3 of the shell. The dissolved CaCO3 and NH3 from protein degradation increase the pH of the surrounding sediment. These results and interpretations are discussed in view of dinosaur eggshell fossilization. This paper provides the first evidence that bacteria significantly impact eggshell preservation.
Phylogenetic community structure and assembly is a burgeoning field in the discipline of community ecology. An array of statistical techniques have been developed in order to study whether or not local assemblages of species are a phylogenetically random, overdispersed, or clustered subset of the regional species pool to which they belong. Phylogenetic clustering or overdispersion depends on aspects of species evolutionary ecology, such as habitat preference, limits of similarity among closely related species, and how traits are inherited in ancestor-descendant relationships. Here I applied the first analysis of phylogenetic community structure and assembly to Plio-Pleistocene large mammal communities of western Eurasia, with the additional goal of verifying if the existing statistics are suitable to be used with fossil data. The results demonstrate that (1) the use of phylogeny in the study of community evolution is feasible with a number of diverse metrics, (2) phylogenetic distance between fossil communities provides an important addition to classic turnover metrics, and (3) the phylogenetic structure of Eurasian Ice-Age mammal communities changed significantly around 1 Ma, when these communities were filled with closely related species from both carnivore and herbivore clades.
Stomatal frequencies of fossil-plant species are used to estimate past pCO2 levels based on the physiological functions of living taxa. There is a demonstrable inverse relationship between increasing pCO2 and stomatal frequency parameters, in which there is a decrease in both stomatal density (SD) and stomatal index (SI). Concentration of CO2 is not the only factor known to affect SD and SI values, which are a product of leaf development and expansion, as studies have shown a positive correlation between SD and light intensity. The present study tests the hypothesis that SD and SI are not influenced by a leaf's physical orientation relative to the sun during the growing season. Sun leaves of northern red oak, Quercus rubra, were collected from trees around the margins of six lakes of the Belgrade Lakes Region, central Maine, United States, in 2007. Lakes in NE–SW, NW–SE, and E–W orientations allowed for sampling of trees exposed to varying light intensities throughout the growing-season day. The SD and SI of each tree were calculated, and statistical comparisons were made between populations exposed to predominant morning or afternoon light intensities for each lake and between populations on lakes of differing orientations. There is no statistically significant difference in either SD or SI between populations growing under different orientations to growing-season sunlight. These data indicate that exposure to various sunlight regimes on opposite sides of a lake does not play a role in the stomatal response as reflected in SD and SI of plants during a single growing season.
Decaying and partially silica-permineralized subfossil plant stems collected from geothermally influenced wetlands of Yellowstone National Park contain evidence of colonization by protists, including heliozoa and chrysophytes. Wetland pools in which the plants and heliozoans occur represent an extreme environment characterized by steady influxes of hot-spring water. Recorded physicochemical conditions in wetland pools reveal relatively high temperatures (often >35 °C), high pH (≤9.1), high conductivity (>3000 µS/cm−1), brackish salinity and elevated concentrations of toxic elements including antimony (Sb), thallium (Tl), mercury (Hg), and arsenic (As). This report contains the first observations of heliozoans and chrysophytes from intercellular sites within decaying plants and adds a previously unreported and extreme environment to their known habitats. Such settings are potential taphonomic windows for preservation of fossil protists.