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Trace fossils on sauropod skeletons from a quarry in fluvial deposits of the Morrison Formation, Wyoming, are used to reconstruct the taphonomic history of the dinosaur bone accumulation. Shallow pits; rosettes; hemispherical pits; thin, curvilinear, branching grooves; and U- to V-shaped linear grooves make up trace fossils found on sauropod skeletons. The traces were interpreted by comparisons to traces on modern bone. Rosettes are circular rings of modified bone and are likely an early stage in the production of shallow pits. They are interpreted as pupation chambers constructed in dried flesh in contact with sauropod bone. Hemispherical pits are circular with a U-shaped cross section and interpreted as dermestid pupation chambers completed in sauropod bone. Thin, curvilinear, branching grooves are semicircular in cross section, form irregular dendritic or looping patterns, and are interpreted as root etchings. U- to V-shaped linear grooves are interpreted as theropod or crocodilian bite marks. Skeletal articulation and condition and distribution of bone modification traces suggest the skeletons accumulated at this site over no more than 3.5 years, with the bulk of the skeletons contributed during the dry season in the final 3–6 months. Carcasses went through all stages of decomposition—including the dry stage, represented by shallow pits, rosettes, and hemispherical pits. Vertebrate scavengers and necrophagous arthropods fed on the carcasses during all decomposition stages prior to burial of the assemblage.
A catastrophically buried stand of calamitean sphenopsids and sigillarian lycopsids is reported from the Middle Pennsylvanian of southwestern Indiana, in the Illinois Basin. The plants were exposed in the highwall of a small surface mine and were rooted in a thin bed of coal (peat), thus representing a flooded and buried swamp surface. Coarse, floodborne silts and sands buried the forest to a depth of <3 m or more, before further incursions of water and sediment truncated the deposit. The rocks are part of the Staunton Formation. Taking up >250 linear meters of exposed highwall surface, the vegetation appears to have been a patchwork of calamitean thickets, with stems perhaps as tall as 3–5 m, within which scattered, but much larger, emergent Sigillaria trees grew, possibly reaching heights of 10–15 m. No ground cover was observed, nor were foliage or reproductive organs attributable to the dominant plants found. The growth of this vegetation in a peat-forming swamp indicates conditions of high water availability, likely in a humid, high-rainfall climate. This kind of plant assemblage, however, cannot be characterized as a rain forest, given that it consisted of medium-height thickets of horsetails with scattered, emergent, and polelike, giant lycopsids, thus lacking a closed upper canopy and possibly only partially shading the ground.
Microfossil tubes with internal thickenings, so-called banded tubes, are a conspicuous but enigmatic element of terrestrial palynomorph assemblages of Silurian to Early Devonian age. Their biological affinities and functions are controversial. Most researchers favor derivation from nematophytes, themselves an enigmatic group of organisms that are often considered to represent early terrestrial fungi-like organisms. Here we present the first transmission electron microscope (TEM) ultrastructural analysis of these banded tubes and show that their walls are homogeneous and lack preserved ultrastructure. Gross wall structure is extremely variable with respect to the nature of the thickenings, suggesting that the tubes were derived from a variety of sources or were highly variable within the source organism. Ultrastructurally, the tubes differ markedly from contemporaneous vascular plant tracheids. We discuss the affinities of the tubes based on the new ultrastructural and structural information, and we conclude that they most likely derive from nematophytes, heterotrophic organisms with fungal-like ecology, where they served as hyphal-like structures, anchoring the organism and transporting nutrients.
We document a new locality for the foraminiferid Bathysiphon at Pacheco Pass, California, a classic blueschist-facies location on the eastern edge of the Franciscan Complex. The nearly featureless, silicified tubes of Bathysiphon cf. aaltoi Miller, 1986 described here are the largest reported from the Franciscan Complex; they are <153 mm long and easily recognized in the field. The rarity of fossils in the Franciscan Subduction Complex has hindered field mapping and, thus, a better understanding of its stratigraphy and structure. Bathysiphon specimens can be used as geopetal indicators, since they occur parallel to bedding at the top of argillaceous layers, as paleocurrent indicators (showing a SSE trend at Pacheco Pass), and as paleobathymetric indicators, suggesting, by their large size, mid-to-lower bathyal depths (2000–4000 m).
We report on exquisitely preserved specimens of freshwater siliceous algae belonging to the classes Synurophyceae (scaled chrysophytes) and Bacillariophyceae (diatoms) from middle Eocene lake sediments in Northern Canada. When considered in the context of closest extant relatives, these microfossils present unequivocal biogeographic and ecological affinities with warm-water ochrophyte assemblages. We have identified scales that are unambiguously assigned to Mallomonas bangladeshica, a chrysophyte now restricted to tropical lake ecosystems. The diatom genus Actinella is also well represented in these sediments, again with the most comparable extant congeners found in tropical to subtropical localities, particularly in the Southern Hemisphere. We surmise that fundamental biogeographic reorganizations among lacustrine algae took place during Eocene hothouse paleoclimates. In this light, future climate warming should be viewed as a potent vector for similar community shifts, with attendant limnological implications.