Assemblages composed of Heleobia parchappii and H. australis constitute the dominant elements in Quaternary deposits of the Pampean Region in the province of Buenos Aires. This study describes and analyzes the degree of preservation of shells of both species recovered from nine Holocene localities in order to describe and quantify taphonomic alterations, evaluate if preservation varied during the Holocene, and assess their utility as paleoenvironmental bioindicators. Heleobia parchappii displayed better overall preservation than H. australis, with little evidence of fragmentation, limited principally to levels with highest densities. On a temporal scale, no significant differences in fragmentation were found, whereas corrasion and luster displayed temporal differences.

The Trypanites ichnofacies is frequently associated with low biotic and trace diversity, and erosional or nondepositional conditions. However, analysis of an extensively exposed, modern, siliciclastic, intertidal hardground community near Thomas Cove, located at Economy Point, Nova Scotia, within the Bay of Fundy, reveals a diverse community of boring, encrusting, and squatting/clinging organisms and a diverse assemblage of sedimentary structures. A high diversity of biota and low diversity, but high abundance, of borings is present along this modern Trypanites-type ichnofacies. Species richness reaches 37 organisms within the study area, and two boring bivalves (Petricola pholadiformis and Zirfaea pilsbryi), which produce Gastrochaenolites-like traces, are present. Eleven distinct depositional subenvironments are identified and are categorized as being either Trypanites-bearing or Trypanites-barren. Analysis of this modern analogue suggests that ancient Trypanites ichnofacies may have been more dynamic and diverse environments than is sometimes interpreted from the rock record.

Concretions are an important source of soft-bodied fossils. In order to determine the controls on exceptional fossilization within concretions, we scored 88 concretion-bearing sites for 11 environmental and compositional variables together with presence/absence of soft-tissue preservation and analyzed their relationships using multiple correspondence analysis (MCA) and qualitative logistic regression. Sites yielding exceptional fossils were distributed randomly through the 88 examples considered, suggesting that exceptional preservation can occur in almost any environment where concretions form. The patterns of interaction of the variables in the MCA revealed that the most important factors controlling exceptional preservation in concretions are related to (1) the potential for fossil preservation in the broader depositional setting (i.e., how likely fossils are to be preserved without concretions but in the same depositional environment) and (2) the rate of concretion growth. In an analysis of the contribution of individual variables, logistic regression showed that two features correlate with the presence of soft-tissue preservation in concretions: (1) fine-grained host lithology, and (2) relatively constant δ¹³C values. The role of the first of these can be tested experimentally. Decay experiments on fish tissue in glass beads of three different sizes and therefore of different permeability showed that decay is inhibited, and mineral precipitation enhanced, in low-permeability sediments. Thus a process of positive feedback promotes exceptional preservation where early cementation results in a rapid decrease in permeability during concretion formation. The second feature, a relatively constant δ¹³C trend, suggests that certain patterns of concretion growth, pervasive growth or concentric growth with one growth layer, are more conducive to fossilization than others.

The rocky, photic benthos of Arctic and Subarctic Biogeographic Regions has a characteristic seaweed flora that includes an extensive high-magnesium calcium carbonate basal layer of crustose coralline red algae. The thickest (10–40 cm) and oldest parts of the crust (previously reported as up to 640–830 years old), primarily at mid-photic depths of 15–25 m, are composed of buildups of the genus Clathromorphum. Due to its annual growth increments and cycling of Mg content with temperature, Clathromorphum has recently been developed as a high-resolution climate archive. The age of the archive is primarily limited by the boring of mollusks that reduce structural integrity, remove the record, and induce local diagenesis. Depressions and gentle slopes in the deeper portions of Subarctic rocky bottoms often collect mixed bioclastic and siliciclastic sediments, including a dense cover of rhodoliths (Lithothamnion glaciale and Lithothamnion tophiforme). In this paper we describe a transition zone of these two environments that forms on cobble/boulder glacial erratic bottoms in northern Labrador. Clathromorphum compactum buildups on the boulders and cobbles projecting through rhodolith beds can be preserved by fine-grained anaerobic sediments that in turn reduce mollusk boring. This significantly enhances preservation and longevity of C. compactum crusts. We describe specimens of ages up to 1200 years BP, and discuss how greater ages can be obtained for archiving high-resolution climate information.

Pycnodonte newberryi oysters accumulated in voluminous shell beds of Late Cretaceous (late Cenomanian) age in shale deposits of the Western Interior Seaway. Analysis of triplicate grid samples from six shell beds in southern Utah shows that the reclining valves of the oyster are disproportionately represented by the inflated left valve, eight times more often than the smaller, flat right valve, and whole valves are rare. The shells nearly always fragment from the commissure toward the thick umbonal half of the shell. These fragmented shells make up more than half of grid samples, and only 0.5% contain predatory drillholes. By contrast, complete shells are drilled nearly 5% of the time, particularly near the umbo. Fragmentation cannot account for this discrepancy because the preponderance of drillholes occurs in the umbonal part of the shell, the part that is always preserved. To understand this paradox, drilled Pycnodonte were collected from a separate site in Utah and drillhole position on the shell was mapped to create a probabilistic model of drillhole sites. Results show that > 60% of drillholes are positioned in the robust part of the umbonal shell, confirming observations in the unfragmented grid-sampled shells. We propose that the deficit in drilled shell fragments can be explained by spatial or temporal mixing of two populations of Pycnodonte that lived under separate predation pressures. Autochthonous shells show greater drillhole incidence and shell completeness, whereas fragmented umbonal shells indicate transportation from a separate environment having lower predation pressure. This study indicates that taphonomic mixing may introduce significant bias in drilling incidence.

Tropical climates reached their northernmost expansion during the early Paleogene greenhouse phase, supporting a paratropical biota as far north as the southern shore of the ancient North Sea. There, relative sea-level fluctuations led to the formation of transgressive-regressive sequences, exposed in open-cast lignite mines in the area of Helmstedt (Lower Saxony, Germany), which record environmental changes at the marine-terrestrial interface. We studied an example from the middle Eocene of the Helmstedt Mine from which we reconstruct ecological successions from open estuary to meandering river environments, which represent vegetation at the Paleogene climatic optimum. In the absence of vertebrate and shelly fossils, environmental interpretations are made exclusively on plant matter in the sediment. Vegetational reconstructions are based mainly on quantitative palynological analyses, supported by paleobotanical and organic-petrographical evidence and confirmed by Principal Component Analysis. Diverse dinocyst assemblages in conjunction with Ophiomorpha-type bioturbation indicate open estuarine conditions. These are succeeded by mangrove, represented by pollen of Rhizophora, Avicennia, Nypa and the form species Psilodiporites iszkaszentgoergyi, and marsh environments, indicated by pollen of Restionaceae, Sparganiaceae/Typhaceae and fern spores. Subsequent lowland mire forests are characterized by a dominance of either the Tricolporopollenites cingulum group (Fagaceae) or triporate pollen of the Triporopollenites robustus/rhenanus complex (Myricaceae/Betulaceae). Within this landscape coexists a meandering river system, represented by channel lag and point-bar deposits of the active channel and by the clastic to lignitic sedimentary fill of an abandoned channel.

Sulfide mineral framboids associated with fossil bones in marine settings may aid in taphonomic reconstructions because framboids reflect the geochemical conditions under which they form. However, the timing and mechanism(s) of framboid formation on bone remain poorly understood. To better constrain the initial formation of framboids during decomposition of bone in marine depositional environments, we simulated aspects of bone decay on the ocean floor and analyzed framboids found on bone surfaces and in the associated sediment. We observed that framboids formed on bone surfaces within one week of experimentation, and were associated with reducing conditions within a dark-colored microbial mat overlain by oxic waters. Statistical and discriminant analyses of elemental data show that bone-hosted framboids formed in situ on the bone surfaces. Close associations of framboids with sulfidic microbial biofilms indicate that bone-hosted framboids resulted from conditions generated during the microbial degradation of bone-associated organic matter. Our results suggest that framboids can form on bone surfaces while bones rest on the seafloor prior to burial and perhaps prior to the so-called sulphophilic stage of whale-fall animal colonization. We compared experimentally produced framboids with published sedimentary framboid populations. Bone-hosted framboids resemble smaller and less variably sized sedimentary framboid populations canonically known to form in anoxic water columns, even though the bone-hosted framboids were overlain by oxygenated conditions. We propose that the period available for framboid growth is shorter on bone surfaces than in sediments, because geochemical conditions that favor sulfide mineral precipitation on bone are transient. Shorter growing periods and localized conditions result in smaller framboid sizes that may not reflect ambient conditions in a water column.

The fossil record of nonbiomineralized chordates is surprisingly extensive. As with most exceptionally preserved fossils, key anatomical features in non-biomineralized chordate fossils are often preserved in less than pristine condition, and potentially only a subset of those originally present. How taphonomic processes impacted on the anatomy of fossils can be constrained by experimental decay of extant analogues. We experimentally decayed tadpoles of Xenopus laevis to document the rate at which various nonbiomineralized tissues degrade and identify changes over time in their ultrastructure. Tissues decayed under identical conditions and sampled at the same time often differed in the level of ultrastructural detail. This is termed an inconsistent pattern of decay and introduces unpredictable taphonomic noise to any dataset. We integrated these results with data from anuran tadpole fossils from the Miocene of Spain and confirm that the nerve cord is less decay resistant than the notochord. Only the notochord is likely to be preserved organically. The nerve cord is only likely to be preserved if replicated in authigenic minerals (calcium phosphate). This is more likely than for other extremely decay-prone tissues, a result of the nerve cord's chemistry in vivo. Two tissues of similar recalcitrance do not, therefore, have equal fossilization potential. On the basis of the experimental and fossil data, structures preserved in amphibians from the Permian Saar-Nahe Basin of Germany are interpreted as fossilized nerve cords, not notochords.