Understanding the drivers of vertebrate fossil preservation is important for paleontologists who rely on well-preserved fossils to study the biological or ecological context of the fauna they represent. Differences in preservation limit the ability to compare biological or ecological change across time. Bones, however, can contain clues of their preservational history: natural voids in skeletal remains are potential sites of mineral precipitation during early and late diagenesis, and the reactive bioapatite provides chemical and physical signals of the postmortem environment. The sensitivity of both infilling minerals and taphonomic alteration to the post-mortem environment has yet to be tested in the fossil record. Bones associated with discontinuity surfaces such as hiatal flooding surfaces and erosional sequence boundaries should face prolonged exposure at the sediment-water interface and/or within the surface mixed layer, increasing the opportunity for modification by taphonomic processes and geochemically disparate (redox) conditions, compared with bones from facies within aggradational intervals, where burial is most likely to be rapid and immediately permanent. µXRF and thin-section-based petrographic analysis of marine mammal bones from the famously fossiliferous Eocene siliciclastics of Wadi al-Hitan, Egypt, reveal strong variation with stratigraphic position: bones found along the sequence boundary show Fe-oxide linings and evidence of desiccation and subaerial exposure, distinct from bones of other settings; a bone from the maximum flooding surface uniquely lacks calcite but has brecciated cancellous bone; bones from systems tracts are variable in the extent of infill but show calcite microfacies consistent with exclusively subaqueous and specifically shallow marine deposition. Early diagenetic signatures were preserved despite many fossil specimens being strongly fractured and infilled by gypsum precipitated during weathering. Bones and their abundant pore space thus acted as time-capsules of early diagenetic conditions, retaining authigenic minerals and other microtaphonomic features linked to their original (Eocene) depositional context.

The fossil record of drill holes on molluscan shells left by carnivorous predators has often been used to test the evolutionary impact of ecological interactions. Ecological experiments document a significant change in the predatory behavior of drillers due to competition and predict a substantial influence of such interaction on predator-prey dynamics. However, it is not always reliable to extrapolate results from experiments to the fossil record. The well-studied bivalve death assemblages from the Bay of Safaga (northern Red Sea) and the Bay of Panzano in the Gulf of Trieste (northern Adriatic Sea) provide a unique opportunity to test if the experimentally observed impact of competition on predatory drilling behavior can be detected in time-averaged molluscan assemblages. The death assemblages of the two regions exhibit unequal molluscan predator-prey abundance ratios (PPAR). Considering that competition among the predators increases when the number of prey individuals per predator decreases, we used PPAR as a new indirect proxy for intra-predatory competition and evaluated its relationship with various measures of drilling predation intensity and predatory behavior. In contrast to the expectations from the behavioral experiments of previous studies, our results show that higher PPAR in the Adriatic assemblage indicating more competitive seascape is associated with higher drilling frequency (DF), and lower edge-drilling frequency (EDF) compared to the Red Sea assemblage. On the other hand, the Adriatic assemblage has higher incidence of incomplete drill holes, which were mostly produced by larger predators. However, a number of taphonomic, ecological and environmental factors may obscure the relationship between PPAR and drilling predation measures observed in the studied death assemblages. Because it is nearly impossible to account for all of these factors in fossil assemblages, the PPAR-based approach of tracking intra-predatory competition may be difficult to apply in deep time, demonstrating the limits of using indirect proxies and experimental results to trace competition in the fossil record.

The Central High Atlas Mountains of Morocco have an extensive record of Lower Jurassic deposits from the Tethyan Ocean. In the Amellago region, Ziz Valley, and Dadès Valley several fossilized reef outcrops preserve benthic foraminifera spanning the Pliensbachian and Toarcian stages. This study analyzes benthic foraminiferal assemblage changes across the bi-phased extinctions at the Pliensbachian/Toarcian boundary and the Jenkyns Event (also referred to as the Toarcian Oceanic Anoxic Event). In Pliensbachian samples, assemblages with abundant Glomospira sp., Glomospirella sp., Siphovalvulina sp., Haurania deserta, Placopsilina sp., Mesoendothyra sp., and Everticyclammina praevirguliana are observed. Following both the Pliensbachian/Toarcian boundary event and the Jenkyns Event, benthic foraminiferal density, evenness, and species richness decreased, indicating these communities underwent ecologic stress; however, loss of diversity was most substantial between samples that pre-date and post-date the Jenkyns Event. Whereas the Pliensbachian/Toarcian boundary event coincides with the demise of the large benthic foraminifera Mesoendothyra sp. and Everticyclammina praevirguliana, the Jenkyns Event was detrimental for most clades of benthic foraminifera, including many small, resilient taxa. Based on the evidence provided, we suggest that the Pliensbachian/Toarcian boundary and the Jenkyns Event were distinct events, potentially caused by distinct environmental perturbations.