A high density of tracks resembling both the ichnogenera Chelonipus and Emydhipus occurs on surfaces of the Lower Cretaceous Tugulu Group at the Huangyangquan tracksite in Wuerhe district (Xinjiang Uyghur Autonomous Region, northwestern China). These ichnotaxa are especially known from Central Europe where they have been found in Triassic and Upper Jurassic–Lower Cretaceous deposits. Tracks are highly variable in morphology due to having been made while walking and swimming over soft substrates. Nevertheless they are diagnostic of turtle trackmakers and are readily distinguished from those of other aquatic vertebrates such as crocodilians and from those of pterosaurs. Abundant turtle body fossils occur in the region helping to provide strong support for this interpretation. The record enlarges our knowledge of turtles, their environment and distribution in the Early Cretaceous of China.

Experimental burial of polychaete (Nereis) and crustacean (Crangon) carcasses in kaolinite, calcite, quartz, and montmorillonite demonstrates a marked effect of sediment mineralogy on the stabilization of nonbiomineralized integuments, the first step in producing carbonaceous compression fossils and Burgess Shale–type (BST) preservation. The greatest positive effect was with Nereis buried in kaolinite, and the greatest negative effect was with Nereis buried in montmorillonite, a morphological trend paralleled by levels of preserved protein. Similar but more attenuated effects were observed with Crangon. The complex interplay of original histology and sediment mineralogy controls system pH, oxygen content, and major ion concentrations, all of which are likely to feed back on the preservation potential of particular substrates in particular environments. The particular susceptibility of Nereis to both diagenetically enhanced preservation and diagenetically enhanced decomposition most likely derives from the relative lability of its collagenous cuticle vs. the inherently more recalcitrant cuticle of Crangon. We propose a mechanism of secondary, sediment-induced taphonomic tanning to account for instances of enhanced preservation. In light of the marked effects of sediment mineralogy on fossilization, the Cambrian to Early Ordovician taphonomic window for BST preservation is potentially related to a coincident interval of glauconite-prone seas.

Occurrences of articulated, multi-element skeletons of edrioasteroids provide evidence of sudden burial and an opportunity for detailed paleoecologic analysis. This study examines two catastrophically buried communities of edrioasteroids from Florence, Kentucky and Sharonville, Ohio. In these two occurrences, the edrioasteroids Isorophus cincinnatiensis, Streptaster vorticellatus, and Carneyella pilea utilized brachiopod and mollusk shells as hard substrates for attachment. Age structure analysis for specimens of Isorophus cincinnatiensis on both pavements show right-skewed distributions that are attributed to high juvenile mortality. Thecae on the Florence pavement have slight bimodal preferential orientation, likely in response to current flow, whereas no preferential thecal orientation was noted for specimens on the Sharonville pavement. Spatial analysis of the Florence pavement indicates a clustered edrioasteroid distribution resulting from multiple edrioasteroids attached to single brachiopod shells. Edrioasteroid margin deformation, in response to inter- and intraspecific competition, provides evidence that edrioasteroids were unable to move once attached to the substrate. Spatial analysis for Isorophus cincinnatiensis on the Sharonville pavement shows few instances of multiple edrioasteroids attached to individual shells. Instead, this clustered distribution suggests enhanced encrustation in areas of enhanced survival (i.e., increased feeding opportunity). The high degree of thecal disarticulation on the Sharonville pavement suggests postmortem bloating and rupture.

This study evaluates encrustation and bioerosion of brachiopods (Bouchardia rosea) and bivalves (Semele casali) occurring on the inner shelf of the Southeast Brazilian Bight, accounting for differences in water depth, sediment type, host size, and time averaging. Frequencies of colonization covary across sites, but brachiopods are more frequently encrusted than bivalves at all sites, although this difference may disappear after standardization for shell size, depending on the chosen metric. Size selectivity during sclerobiont colonization appears to change as a function of their population density, rather than substrate differences between hosts. Sediment grain size and composition do not appear to exert environmental controls on encrustation or bioerosion, nor does either vary as a function of water depth alone. Radiocarbon-calibrated aspartic acid racemization dating of individual host valves shows similar age ranges and age structures for both hosts. Both epifaunal brachiopods and infaunal bivalves are colonized rapidly, within years to decades, with no further increase over millennial timescales. Rapid burial and sequestration from sclerobiont larvae is inconsistent with rapid postmortem exhumation and encrustation of infaunal bivalves, and indicates a brief temporal window for colonization. The relative abundance of sclerobionts is volatile over the time interval represented by dated valves, but temporal stability is seen in presence-absence data for epibiont and endobiont taxa. These results support the utility of taphonomic deployment experiments for investigating long-term patterns of hard-substrate colonization, but indicate careful consideration of host size is required for comparison of sclerobiont assemblages within or among taxa.