Condensed transgressive shell beds, rich in paleobiological information, are common in the Phanerozoic stratigraphic record, but their interpretation is complicated by the uncertain amount of time that each deposit represents. Miocene strata exposed in the Calvert Cliffs (Maryland, USA) are known for a series of regionally extensive, densely packed, meters-thick shell beds that serve as global exemplars of shallow-water condensation during marine transgression and onlap. Applying Sr isotope stratigraphy to calcitic scallops from the base and top of the oldest of these beds (Shattuck Zone 10), we demonstrate that its most densely fossiliferous part accumulated over the interval of 16.60–15.95 Ma, reflecting approximately 0.65 ±0.20 Myr of skeletal accumulation within the Miocene Climatic Optimum, with a likely 0.15 Myr-scale of time averaging per each firmground-bounded subunit. Both of these estimates are an order of magnitude longer than previous best estimates based on radiocarbon-dated Holocene analogs. Sr isotopes confirm subtle low-angle erosional beveling of the main body of Zone 10, truncating 0.3-Myr of record in updip sections, and demonstrate that a down-dip wedge of less shelly sand is an entirely younger (by ∼ 0.5 Myr) interleaved body. This condensation, beveling, and inter-shingling within Zone 10 quantified here sets a precedent for the magnitude of lateral and vertical temporal variability within condensed transgressive deposits, relevant to paleobiologic and other geohistorical analysis, and justifies the interpretation of comparably complex temporal fabrics based upon similar physical stratigraphic features found elsewhere in this and other very thin stratigraphic records.

As quantitative tools, drill holes have been used to calculate predation frequencies in time and space. These traces can also inform predator preference and some strategies predators use to drill on prey (e.g., edge drilling, site stereotypy, or alternative modes of predation when there is no drill hole). In this study, our goal was to leverage the informative power of drill holes to characterize the predatory habits of muricid gastropods from the central coast of Chile. We integrated information from experiments and death assemblages (DAs) to unveil the predatory strategy of Ancathina monodon, Crassilabrum crasilabrum, and Concholepas concholepas on the mobile gastropod Tegula tridentata and the sessile bivalve Perumytilus purpuratus. Experiments supported previous findings for predatory strategies (basal spine for Ancathina and alternative modes of predation for Concholepas), and showed the stereotypic predation of Crassilabrum on Tegula—a herbivore that is devastating subtidal kelp forests. Based on drill holes from DAs, at least 11 molluscan families are consumed by muricids in these communities. DAs also helped validate the stereotypic predation of Crassilabrum on Tegula, as drill holes were found in the same position both in experiments and DAs. Despite their thinner shells, mytilids were well represented in DAs and were found with drill holes in the five locations sampled. We describe for the first time the predatory strategy of Crassilabrum in Chile and confirm that muricids other than Concholepas are active predators on subtidal rocky habitats from the southeastern Pacific Ocean, a region that is still understudied.

Neoichnology, the study of the traces of extant organisms, provides a vital tool for better understanding trace fossils. We conducted neoichnological experiments to test hypotheses regarding producers and the effects of substrate conditions on trace fossils produced by aquatic to amphibious arthropods. Our experiments comprised two protocols: subaerial and subaqueous substrates; and we utilized five arthropods: fully aquatic ostracods (Ostracoda indet.), to amphibious horseshoe crabs (Limulus polyphemus), shore crabs (Carcinus maenas), and scarlet hermit crabs (Paguristes cadenati), and the largely terrestrial sea slaters (Ligia oceanica). The different arthropods were observed performing locomotory, resting/stationary, and feeding behaviors, which all resulted in different traces influenced by the substrate conditions and their preference for living in and out of water. In general, trace depth increased with arthropod mass and, for each individual arthropod except the scarlet hermit crab, trace depth was also greater in subaerial compared to subaqueous substrates. In the majority of cases, comparisons with selected trace fossils supported previous hypotheses as to their producers. The traces of horseshoe crabs, shore crabs, sea slaters, and ostracods resembled the ichnotaxa Kouphichnium, Laterigradus, Pterichnus, and Mermia, respectively. Other experimental work has shown hermit crabs produce traces similar to Coenobichnus and our results further increase the range of trace morphologies that can be attributed to hermit crabs. The results of this research have bearing on debates in ichnology where the interpretation of producers and substrate conditions at the time of trace formation are critical, such as the trace fossil evidence for the colonization of land.

Low-level drone photogrammetry is a technique that allows for the construction of surface orthomosaics and elevation models. Despite being used for a wide range of geological applications, these types of datasets have not yet been explored from a neoichnological perspective. This study uses three examples of tidal flats from the Bay of Fundy to demonstrate the usefulness of 3D photogrammetry in the collection of high-resolution neoichnological datasets. The first site is a bar top along the Petitcodiac River that is situated between a salt marsh and tidal channel margin. The second site, which is located along the Shepody River, represents a laterally accreting channel margin and thus has a relatively high relief. In contrast, the final site comprises a gently sloping tidal flat that is far from the influence of a major tidal channel. Spatial analysis of the shorebird tracks at each site was used to assess the relationship between shorebird track distributions (e.g., track density, stride orientation, stride length) and various environmental and ecological factors (e.g., topography, tidal current direction, invertebrate prey distributions). Additionally, morphological analysis of the tracks was used to assess variations in substrate cohesiveness, which is the environmental factor that exhibited the most variability at the study locations. The track record at each site represents a shorebird flock that traversed the tidal flats in such a way as to optimize foraging success. As a result, the abundance and availability of macrobenthic invertebrate prey was the primary factor contributing to shorebird track density. This paper aims to assess local-scale variations in tidal flat substrate cohesiveness and provide context for the interpretation of fossilized shorebird trackways.

A Neogene hematite-goethite concretionary ‘ironstone’ horizon in laterized fluvial sediments in the Massif du Sud of New Caledonia yields abundant fossil dicotyledonous angiosperm leaves. The leaves are preserved in iron oxide, mainly goethite, which replicates the morphology and anatomy of the leaf tissues and comprises 73% of the matrix. Organic remains are minimal and associated with aluminosilicate clay. Leaf tissues are preserved three-dimensionally in multiple ways including casts/molds, permineralization/petrifaction, and replacement. Although the mesophyll is less well preserved, reflecting its greater susceptibility to decay, cellular details of vascular and epidermal tissues are commonly evident. Analyses of leaves from an analogous modern setting reveal the early encrustation and impregnation of tissues by amorphous iron-oxides and clays in association with a microbial biofilm. We propose a taphonomic model in which the fossil leaves, like their modern counterparts, were permeated by iron oxides due to the high availability of iron derived from weathering of ultramafic basement. In contrast to the iron-rich aluminosilicate coatings that form in relatively iron-poor settings, the unusually high concentration of dissolved iron oxides permitted rapid anatomical preservation.