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The large euthycarcinoid arthropod Mictomerus melochevillensis from the middle Cambrian-Furongian Potsdam Group of Quebec occurs as three-dimensional casts at the end of Cruziana- and Didymaulichus-like trace fossils. This association provides a rare opportunity to test functional morphological hypotheses about these animals, it provides a framework for understanding how arthropods can be sand-cast in three dimensions, and it suggests that euthycarcinoids may have burrowed into mud as an antidesiccation strategy. In the coeval Elk Mound Group of Wisconsin, the phyllocarid arthropod Arenosicaris inflata occurs on the same beds as Cruziana-like and Rusophycus traces; together with morphologically similar ropelike traces, they are interpreted as having been produced by phyllocarids. These traces preserve the earliest known ethological evidence of phyllocarid crustaceans, and imply that Cambrian phyllocarids employed antidesiccation and possibly feeding strategies still used by modern intertidal leptostracan phyllocarids.
The upper Ediacaran Gaojiashan Lagerstätte (551–541 Ma) in southern Shaanxi Province, South China, hosts a variety of soft-bodied or lightly biomineralized tubular fossils (Shaanxilithes, Conotubus, Gaojiashania, Sinotubulites, and Cloudina) and calcareous microfossils (Protolagena). This study focuses on the fossiliferous middle Gaojiashan Member at the Gaojiashan section, where pyritization of soft-bodied or lightly skeletonized tubular fossils is the primary mode of preservation. Integrated paleoecological, sedimentological, and taphonomic analysis shows that event deposition played an important role in the biostratinomy of the Gaojiashan Lagerstätte. Gaojiashan fossils, particularly pyritized fossils, preferentially occur in mm-thick, normally graded calcisiltite-siltstone layers, interpreted as distal event deposits, but are rarely present in calcilutite-mudstone beds. Two taphofacies are recognized in the middle Gaojiashan calcisiltites-siltstones, on the basis of biostratinomic data (e.g., fossil fragmentation and disarticulation). Both taphofacies contain fossils (Conotubus, Gaojiashania, and Protolagena) that were buried in situ by distal event deposits below the average storm wave base; evidence for in situ burial includes oblique orientation, rejuvenation, growth interruption, and reorientation. This research represents one of the few biostratinomic studies of Precambrian Lagerstätten. Results show that the Gaojiashan Lagerstätte, like many Phanerozoic Konservat-Lagerstätten, was influenced strongly by event deposition that provides an obrution mechanism for quick burial. Although some taphonomic processes—those responsible for Ediacara-type and Burgess Shale-type preservation—may be restricted to certain geological time intervals, others such as sedimentary obrution and rapid burial may have been continuously and universally important in exceptional preservation throughout geologic history.
Bone fossilization is generally thought to be predominantly slow and geochemically controlled, whereas soft-tissue preservation is rapid and microbially enhanced. Microbial destruction of bone has been well researched, but potential preservational influences of microbes on bone are relatively unstudied. Building on previous work, this study examined evidence for microbially induced mineralization of bone buried in a simulated terrestrial setting using an actualistic, experimental approach designed to allow both biotic and abiotic precipitation to occur. Four trials were conducted in 2002 by burying bleached fresh bone cubes in river sand through which calcium carbonate saturated water was percolated. A “natural” trial used unmodified river sediment with natural bacterial populations. Two trials were run with bleach or sodium azide to reduce or eliminate bacterial populations. A fourth trial used washed, bleached sediment with reintroduced bacteria. After one week, the natural trial showed signs of mineral precipitation that cemented sand grains to the bone cubes. Bones from both the natural and washed trials were completely covered by adherent sediment after six weeks. After twelve weeks, cancellous bone in the nonsterile trials was permineralized while antiseptic trials and compact bone showed no indications of permineralization. Nonsterile trials also exhibited partially calcified fungal hyphae and possible lithified bacteria. This study provides additional experimental evidence that microbes are important agents of fossilization for bone as well as soft tissue. It also supports the inference that microbially induced mineral precipitation can play a significant role in bone fossilization by enhancing bone survival through early permineralization until apatite recrystallization occurs.
Palynological investigations of the mid-Cretaceous, delta-influenced Malha Formation and superjacent transgressive Galala Formation exposed at Gebel El Minshera, north Sinai, Egypt, have yielded a sparse but biostratigraphically useful record of spores, pollen, and rare dinoflagellate cysts. A representative of the pollen genus Tricolporites, recovered 18 m above the base of the Malha Formation, is post-Aptian in age. An interval comprising the upper Malha Formation and lower Galala Formation is dated as middle Albian/middle Cenomanian based on the occurrence of Elaterosporites klaszii at the base and Afropollis jardinus at the top. A palynoflora from the upper Malha Formation, which includes ephedroids as well as Elaterosporites, has affinities with the Albian–Cenomanian Elaterates Province. The presence of palynomorphs associated with active fluvio-deltaic settings supports a proximal deltaic environment for the deposition of the Malha Formation, with the superjacent Galala Formation representing a subsequent marine flooding of the delta. A distinctive monospecific assemblage of the dinoflagellate cyst Subtilisphaera senegalensis in the upper part (Cenomanian) of the Galala Formation reflects an ecologically stressed, marginal-marine environment. This assemblage constitutes the first record of the mid-Cretaceous Subtilisphaera ecozone in Egypt and indeed east of Morocco, and in deposits as young as Cenomanian. The Malha and lowermost Galala Formations are characterized by type III–VI kerogen, which is gas prone but having little potential to produce hydrocarbons. Spore-pollen color indicates thermal maturity at the transitional to over-mature level, which is anomalously high when compared with equivalent deposits in the region.
The Juniata Formation comprises Upper Ordovician sandstone and mudstone that crops out in the Appalachian region of the eastern United States from Pennsylvania to Tennessee. An outcrop at Potters Mills, central Pennsylvania, has previously been attributed to a terrestrial environment. Because this outcrop contains numerous sub-vertical burrows and evidence for pedogenesis, it has regularly been cited as the oldest evidence for several aspects of continental ecosystem development, including the first evidence for terrestrial infauna and animal-plant interactions. We present evidence from both original fieldwork and published literature that collectively sheds considerable doubt on previous interpretations. The evidence suggests that the Juniata Formation at Potters Mills was deposited in a marginal marine setting and, as such, no evidence for early life on land can be inferred from its strata. This has significant implications for the numerous studies that have cited the Juniata Formation as providing a key record of early terrestrial evolution. Removing it from the dataset of studies that deal with the history of life on land, we conclude that currently the majority of fossil evidence from localities worldwide supports the appearance of terrestrial infauna and animal-plant interactions in the Silurian–Devonian.
Bioglyphs are features in burrow or boring walls produced by such animal activity as scratching, drilling, plucking, gnawing, poking, and etching. Bioglyphs are important aspects to consider when making paleoethologic interpretations of trace fossils, because they can offer direct clues to understanding the mechanism of excavation of the trace fossil, the identity of the tracemaker, the purpose of the burrow or boring, and the character of the sediment in which the trace fossil has been produced.