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"Green River Formation."
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Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara)
Background
Lepidosauria (lizards, snakes, tuatara) is a globally distributed and ecologically important group of over 9,000 reptile species. The earliest fossil records are currently restricted to the Late Triassic and often dated to 227 million years ago (Mya). As these early records include taxa that are relatively derived in their morphology (e.g.
Brachyrhinodon
), an earlier unknown history of Lepidosauria is implied. However, molecular age estimates for Lepidosauria have been problematic; dates for the most recent common ancestor of all lepidosaurs range between approximately 226 and 289 Mya whereas estimates for crown-group Squamata (lizards and snakes) vary more dramatically: 179 to 294 Mya. This uncertainty restricts inferences regarding the patterns of diversification and evolution of Lepidosauria as a whole.
Results
Here we report on a rhynchocephalian fossil from the Middle Triassic of Germany (Vellberg) that represents the oldest known record of a lepidosaur from anywhere in the world. Reliably dated to 238–240 Mya, this material is about 12 million years older than previously known lepidosaur records and is older than some but not all molecular clock estimates for the origin of lepidosaurs. Using RAG1 sequence data from 76 extant taxa and the new fossil specimens two of several calibrations, we estimate that the most recent common ancestor of Lepidosauria lived at least 242 Mya (238–249.5), and crown-group Squamata originated around 193 Mya (176–213).
Conclusion
A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid. Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora. Most major subclades within Squamata originated in the Cretaceous postdating major continental fragmentation. The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.
Journal Article
Crystal structure of abelsonite, the only known crystalline geoporphyrin
The crystal structure of the unique nickel porphyrin mineral abelsonite, NiC31H32N4, has been solved using direct methods with 2195 independent reflections to a final R1 = 0.0406. Abelsonite crystallizes in the triclinic space group P1, with Z = 1 and unit-cell parameters a = 8.4416(5) A, b = 10.8919(7) A, c = 7.2749(4) A, α = 90.465(2)°, β = 113.158(2)°, and γ = 78.080(2)° at the measurement condition of 100 K, in very good agreement with previous unit-cell parameters reported from powder diffraction. The structure consists of nearly planar, covalently bonded porphyrin molecules stacked approximately parallel to (111), and held together by weak intermolecular Van der Waals forces. The molecules within a layer are slightly tilted such that molecular planes do not overlap, and an up-turned ethyl group on one molecule sits adjacent to a down-turned ethyl group on a neighboring molecule of the same layer. Layers are stacked along a vector normal to (111) such that an aromatic ring at one corner of the molecule lies directly above the opposite aromatic ring of the molecule below. Although a single molecule does not quite possess 1 symmetry, matching ethyl groups at roughly opposite ends of the molecule enable orientational disorder, in which molecules can randomly adopt one of two different orientations while still stacking in the same manner. The aggregate of these two random orientations produces an overall symmetry of P1.
Journal Article
Fossil Palm Flowers from the Eocene of the Rocky Mountain Region with Affinities to Phoenix L. (Arecaceae: Coryphoideae)
Premise of research. Numerous trimerous fossil flowers have been collected from Eocene strata in Wyoming, Utah, and Colorado. While many specimens have been assigned tentatively to Arecaceae, they have not been described formally, and their systematic placement within this large family has not been determined.
Methodology. Fossils from the Eocene Bridger, Green River, and Wind River Formations were photographed, described, and measured. Pollen extracted from a stamen was studied by transmitted light, epifluorescence, and scanning electron microscopy. The floral and pollen morphological characters were compared to extant and fossil genera of angiosperms with a focus on Arecaceae.
Pivotal results. Both macromorphological and palynological characters agree with assignment of the fossils to the extant genus Phoenix (L.). This is significant because Phoenix is native to Africa and southeast Asia today, but these fossils indicate a much broader distribution in the past. In addition, Phoenix cannot tolerate extensive freezing conditions, indicating a mostly frost-free climate when it was growing in the Rocky Mountain region during the Eocene.
Conclusions. These fossil flowers represent a new species, Phoenix windmillis S.E. Allen sp. nov., significant because it is the first confirmation of the genus in the North American fossil record. The absence of pinnate induplicate palm leaves in the Eocene of North America that could be interpreted as Phoenix demonstrates the need to examine dispersed reproductive organs, as well as leaves, in evaluating fossil floras.
Journal Article
An examination of the hypersaline phases of Eocene Lake Uinta, upper Green River Formation, Uinta Basin, Utah
The early evolution of ancient Lake Uinta has been the focus of significant study due to the enormous hydrocarbon reserves in the Uinta Basin’s lower to middle Green River Formation. In contrast, the upper Green River Formation, which includes strata recording the lake’s highest level (Mahogany zone), as well as three previously poorly delineated hypersaline phases, is less understood but still important for developing a complete lacustrine system evolutionary model. Detailed descriptions and mineralogy from several cores, as well as examination of geophysical logs from hundreds of oil and gas wells, were used to help delineate these three hypersaline lake phases and better define the events related to the infilling of Lake Uinta. Lake Uinta’s first hypersaline phase, recorded in the Uinta Basin, occurred synchronously with the upper R-6 and Mahogany zone deposition. Evaporite minerals, mostly nahcolite nodules and small shortite crystals, were deposited in the basin’s paleo-depocenter in central Uintah County. The second hypersaline phase is represented by a nearly basin-wide small-evaporite-crystal facies (both nahcolite and shortite), as well as a large-evaporite-nodule facies (nahcolite), also centered on the basin’s eastern paleo-depocenter in central Uintah County. Near the end of the second hypersaline phase, sediments originating from the southeast and north began to infill the lake, pushing the paleo-depocenter to the west. The third hypersaline phase is represented by a thick sequence of lacustrine sediments with disseminated evaporite minerals (nahcolite, shortite, and other more exotic sodium evaporite minerals) and bedded salts (halite and trona) centered in north-central Duchesne County.
Journal Article
Diagenetic sequestration of rare earths and actinides in phosphatic oil shale from the lacustrine Green River Formation (Eocene), Utah, USA: an SEM and LA-ICP-MS study
The upper Green River Formation of the eastern Uinta Basin of Utah comprises variably organic-rich mudrock deposited in a stratified, alkaline lake that fluctuated in size and in hydrology from open to evaporitic. Beds of oil shale, representing periods of deep lake, suboxic-anoxic deposition include examples with anomalously high phosphate and toxic trace-metal levels, as determined by whole rock X-ray diffraction, scanning electron microscopy (SEM), and both solution and laser-ablation (LA) inductively coupled plasma-mass spectrometry (ICP-MS). The SEM identifies an early, pre-compaction, diagenetic succession of euhedral rhombic dolomite and high-Mg-calcite, nodular pyrite, blocky low-Mg calcite, and microcrystalline carbonate fluorapatite (CFA). LA-ICP-MS indicates the CFA intervals have distinct lower and upper margins where P content rises from ~0.079 to ~3.2% across 2–3 cm of section. Enrichments of rare earth elements (REEs) and actinides (Th, U) show a complex correlation with the phosphatic margins. Light REEs average a tenfold enrichment at the outer margins with progressively heavier REEs exhibiting up to 20-fold enrichment toward the inner margin (Lu from 0.15 to 2.63 ppm). Actinide abundances also increase tenfold (U from ~5 to ~80 ppm) toward the inner margin. There is greatest similarity between Th and the Ho distributions and between U and Lu. This is a similar distribution to what elsewhere has been found in fossil bone and teeth. The microcrystalline CFA is interpreted to have precipitated (or recrystallized from a precursor phosphate) when the rate of dissolved P being generated from organic-matter breakdown exceeded P diffusion rates into the water column, allowing for P supersaturation. As the crystallites grew, diffusion of REE and actinide ions and complexes from surrounding porewaters into the concreting phosphate occurred only until pores were occluded and permeability dropped. As with fossil bone, at the outer margin of the phosphate interval, this allowed for fractionation and preferential substitution of Ca cations in the CFA lattice by light REEs of similar ionic radius. Heavier REEs and actinides of smaller ionic radius diffused further into margin of the phosphate interval.
Journal Article
The same picture through different lenses: quantifying the effects of two preservation pathways on Green River Formation insects
Insects in the fossil record are generally preserved in lacustrine shales or in amber. For those in lacustrine shales, preservation is usually via keroginization or mineralization. Given the extended period of microbial decay required to generate ions for mineralization, there is a predicted inherent bias toward lower preservation quality for this pathway by most taphonomic indices compared with keroginization. This study tests this hypothesis by comparing multiple measures of preservation quality between sites with similar sedimentology in the Eocene Green River Formation of Colorado. Here, insects are either mineralized in iron oxides (likely after pyrite) at the Paleoburn site or keroginized at the Anvil Points site. Generally, the prediction that keroginization preserves soft-bodied fossils with higher preservational quality than mineralization is affirmed, but with some caveats. Beetles, known for their robust cuticles, are proportionately more abundant at the Paleoburn site, but eight of the nine orders recorded are shared between sites. As predicted, insects show lower preservation fidelity at the Paleoburn site, but they also show higher degrees of disarticulation. This second bias should be acquired primarily during the biostratinomy stage, and not early diagenesis. Nonetheless, higher-energy biostratinomic conditions may be compatible with taphonomic conditions that promote mineralization over keroginization. Comparing the inherent taphonomic bias of different preservation pathways is often difficult, since fossil deposits may be preserved millions of years or thousands of kilometers apart. By studying two different preservation pathways of insects within the same formation, we can affirm that keroginization does indeed preserve recalcitrant organic matter with higher quality than pyritization or iron-oxide mineralization. Additionally, some guidelines can be proposed concerning the body parts and taxa that can be compared, and for what purpose, when contrasting mineralized and keroginized soft-bodied deposits.
Journal Article
Fossil leaf economics quantified: calibration, Eocene case study, and implications
Leaf mass per area (MA) is a central ecological trait that is intercorrelated with leaf life span, photosynthetic rate, nutrient concentration, and palatability to herbivores. These coordinated variables form a globally convergent leaf economics spectrum, which represents a general continuum running from rapid resource acquisition to maximized resource retention. Leaf economics are little studied in ancient ecosystems because they cannot be directly measured from leaf fossils. Here we use a large extant data set (65 sites; 667 species-site pairs) to develop a new, easily measured scaling relationship between petiole width and leaf mass, normalized for leaf area; this enables MA estimation for fossil leaves from petiole width and leaf area, two variables that are commonly measurable in leaf compression floras. The calibration data are restricted to woody angiosperms exclusive of monocots, but a preliminary data set (25 species) suggests that broad-leaved gymnosperms exhibit a similar scaling. Application to two well-studied, classic Eocene floras demonstrates that MA can be quantified in fossil assemblages. First, our results are consistent with predictions from paleobotanical and paleoclimatic studies of these floras. We found exclusively low-MA species from Republic (Washington, U.S.A., 49 Ma), a humid, warm-temperate flora with a strong deciduous component among the angiosperms, and a wide MA range in a seasonally dry, warm-temperate flora from the Green River Formation at Bonanza (Utah, U.S.A, 47 Ma), presumed to comprise a mix of short and long leaf life spans. Second, reconstructed MA in the fossil species is negatively correlated with levels of insect herbivory, whether measured as the proportion of leaves with insect damage, the proportion of leaf area removed by herbivores, or the diversity of insect-damage morphotypes. These correlations are consistent with herbivory observations in extant floras and they reflect fundamental trade-offs in plant-herbivore associations. Our results indicate that several key aspects of plant and plant-animal ecology can now be quantified in the fossil record and demonstrate that herbivory has helped shape the evolution of leaf structure for millions of years.
Journal Article
Systematics and phylogeny of the Zygodactylidae (Aves, Neognathae) with description of a new species from the early Eocene of Wyoming, USA
Zygodactylidae are an extinct lineage of perching birds characterized by distinct morphologies of the foot and wing elements. Although the clade has a complex taxonomic history, current hypotheses place Zygodactylidae as the sister taxon to Passeriformes (i.e., songbirds). Given the rather sparse fossil record of early passeriforms, the description of zygodactylid taxa is important for inferring potentially ancestral states in the largest radiation of living birds (i.e., the ∼6,000 species of extant passeriforms). Despite the exceptional preservation of many specimens and considerable species diversity in Zygodactylidae, the relationships among species have not been previously evaluated in a phylogenetic context. Herein, we review the fossil record of Zygodactylidae from North America and describe five new well-preserved fossils from the early Eocene Green River Formation of Wyoming. Two specimens are identified as representing a new species and the first records of the taxon Zygodactylus outside Europe. Anatomical comparisons with previously named taxa and the results of phylogenetic analysis including newly described specimens and previously named zygodactylid taxa provide the first hypothesis of the species-level relationships among zygodactylids. The monophyly of Zygodactylidae is supported in these new analyses. However, the monophyly of Primozygodactylus and the taxonomic distinction between Zygodactylus and Eozygodactylus remain unresolved and would likely benefit from the description of additional specimens.
Journal Article
Mapping prehistoric ghosts in the synchrotron
The detailed chemical analysis of fossils has the potential to reveal great insight to the composition, preservation and biochemistry of ancient life. Such analyses would ideally identify, quantify, and spatially resolve the chemical composition of preserved bone and soft tissue structures, but also the embedding matrix. Mapping the chemistry of a fossil
in situ
can place constraints on mass transfer between the enclosing matrix and the preserved organism(s), and therefore aid in distinguishing taphonomic processes from original chemical zonation remnant within the fossils themselves. Conventional analytical methods, such as scanning electron microscopy (SEM) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) have serious limitations in this case, primarily, an inability to provide large (i.e., decimeter) scale chemical maps. Additionally, vacuum chamber size and the need for destructive sampling preclude analysis of large and precious fossil specimens. However, the recent development of Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) at the Stanford Synchrotron Radiation Lightsource (SSRL) allows the non-destructive chemical analysis and imaging of major, minor, and trace element concentrations of large paleontological and archeological specimens in rapid scanning times. Here we present elemental maps of a fossil reptile produced using the new SRS-XRF method. Our results unequivocally show that preserved biological structures are not simply impressions or carbonized remains, but possess a remnant of the original organismal biochemistry. We show that SRS-XRF is a powerful new tool for the study of paleontological and archaeological samples.
Journal Article