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The Rockslide Formation (middle Cambrian, Drumian, Bolaspidella Zone) of the Mackenzie Mountains, northwestern Canada, hosts the Ravens Throat River Lagerstätte, which consists of two, 1-m thick intervals of greenish, thinly laminated, locally burrowed, slightly calcareous mudstone yielding a low-diversity and low-abundance fauna of bivalved arthropods, ‘worms', hyoliths, and trilobites. Also present are flattened, circular, black carbonaceous objects averaging 15 mm in diameter, interpreted as coprolites preserved in either dorsal or ventral view. Many consist of aggregates of ovate carbonaceous flakes 0.5–2 mm long, which are probably compacted fecal pellets. Two-thirds contain a variably disarticulated pair of arthropod valves, and many also contain coiled to fragmented, corrugated ‘worm' cuticle, either alone or together with valves. A few contain an enrolled agnostoid. In rare cases a ptychoparioid cranidium, agnostoid shield, bradoriid valve, or hyolith conch or operculum is present; these are taken to be due to capture and ingestion of bioclasts from the adjacent seafloor. Many of the coprolites are associated with semi-circular spreiten produced by movement of the worm-like predator while it occupied a vertical burrow. Its identity is unknown but it clearly exhibited prey selectivity. Many coprolites contain one or more articulated hyoliths, ptychoparioid trilobites, or outstretched agnostoid arthropods oriented dorsal side up. These are interpreted as opportunistic coprovores drawn to the organic-rich fecal mass while it was lodged near the entrance to the burrow. This argues that hyoliths were mobile detritivores, and agnostoids were mainly nektobenthic or benthic, like the ptychoparioid trilobites. Fecal matter was probably an important source of nutrition in the Cambrian food web.
Caves are important sites of fossil preservation, especially for Quaternary vertebrates. Taphonomic processes operating in caves are not well understood and have never been experimentally examined. This study focuses on the potential role of bat guano, which impacts environmental biogeochemistry and serves as the base of the food chain in cave ecosystems. The presence or absence of guano is expected to be a major control of preservation potential in caves. Bats first appear in the fossil record in the early Eocene so bat guano likely influenced cave preservation only during the Cenozoic. This is a probable megabias of the cave fossil record. Microcosm experiments were used to determine the impact of guano presence and composition, moisture, temperature, and time on preservation potential of small mammal bones, leaves, and crickets. Guano came from insectivorous and frugivorous bats. The guano of insectivorous bats has an acidic pH, while the guano of frugivorous bats is close to neutral. Lab studies were supplemented with field experiments at Crumps Cave, Kentucky. Leaves and crickets were better preserved in the guano of insectivorous bats, while bones showed recrystallization after burial. Leaves and crickets buried in the guano of frugivorous bats were quickly colonized by fungi and mostly destroyed, while only a few bones showed signs of fungus and degradation. Microcosms with a higher moisture content showed greater degradation, while time and temperature had less of an effect. Bones buried in both types of guano decayed much more rapidly than in sand. Bones buried in situ in cave sediments showed little degradation over three months. These results provide insight into the variable impact of environmental conditions on the taphonomy of Quaternary vertebrates and plants.
Although studied for more than a century, the preservation mechanisms of soft-bodied organisms in Lagerstätten remain disputable. One aspect of this phenomenon, the role of sediments in the decay and preservation of soft tissues, is understudied. We present the results of an 18-month decay experiment that shows the difference between the preservation of the crustacean Artemia salina buried in marine water and inside clay sediment. We found that the decay of the external tissues of A. salina is slower in the sediment than in marine water, while the internal anatomy decays rapidly in both settings. This results in the formation of exuviae-like structures, accounted for not by the recalcitrance of external tissues, but by the burying conditions in the thick marine sediment. The experiment indicates the importance of organic-mineral interactions in the understanding of the taphonomic retarding of soft-tissue decay and the persistence of fine external anatomical features.
A recently discovered tyrannosaurid metatarsal IV (SWAU HRS13997) from the uppermost Cretaceous (Maastrichtian) Lance Formation is heavily marked with several long grooves on its cortical surface, concentrated on the bone's distal end. At least 10 separate grooves of varying width are present, which we interpret to be scores made by theropod teeth. In addition, the tooth ichnospecies Knethichnus parallelum is present at the end of the distal-most groove. Knethichnus parallelum is caused by denticles of a serrated tooth dragging along the surface of the bone. Through comparing the groove widths in the Knethichnus parallelum to denticle widths on Lance Formation theropod teeth, we conclude that the bite was from a Tyrannosaurus rex. The shape, location, and orientation of the scores suggest that they are feeding traces. The osteohistology of SWAU HRS13997 suggests that it came from a young animal, based on evidence that it was still rapidly growing at time of death. The tooth traces on SWAU HRS13997 are strong evidence for tyrannosaurid cannibalism—a large Tyrannosaurus feeding on a young Tyrannosaurus.
Fluvial transport is recognized as a common manner by which bone assemblages forming in or near moving water can be taphonomically modified. Here we study an assemblage of 38 cow carcasses, killed during a mass-mortality event and deposited in a fluvial system (the Yellowstone River of eastern Montana), over the course of three years. Seven of the 38 carcasses were observable throughout the study, allowing assessment of patterns of disarticulation and element loss with respect to time and microenvironment. The probability of loss of individual elements corresponds broadly with Voorhies' bone transport experiments, modified to account for disarticulation order. Evidence of scavenger-mediated bone loss is minimal, despite abundant evidence of the presence of scavenging taxa. Individual carcasses show different patterns of element loss, depending on the magnitude of fluvial energy that the carcass was subject to. Carcasses in very high energy regimes lose all elements immediately on disarticulation, whereas carcasses in lower energy regimes show a more typical lag-assemblage profile. Comparison of disarticulation patterns from similar modern and fossil assemblages indicates the Yellowstone cow assemblages define part of a widely expressed spectrum of bone modification in fluvial systems, strongly controlled by the magnitude of transport energy to which bone assemblages are exposed.