The famous Rancho La Brea tar seeps of Southern California trapped thousands of Pleistocene and early Holocene vertebrates, preserving them as jumbled columns of millions of disarticulated bones. Previous work has contributed to a hypothetical entrapment scenario, however, it lacks detail in the period between the time the animals perished and the permeation of their bones with tar. Additionally, previous work has shown that skeletal elements moved apart from each other at least 1–3 meters but it is unclear whether this movement occurred near the surface of the tar, soon after submersion, or later after burial by sediment and compaction. To help answer these questions of disarticulation and transport, we conducted an actualistic experiment to record the progress of microbial succession and skeletonization of specimens in tar. We submerged dismembered bobcat (Lynx rufus) carcasses in an undisturbed tar seep and recorded the progress of microbial faunal changes and tissue decay. Microbial communities differed between tar environments and tissue decay, and changes in microbial communities across the stages of decay indicate rapid microbial succession, with the microbes most involved in the decay likely originating from the liquid surface tar. The minimum time to achieve clean bone was 40 days, from which we conclude that a surficial process may have been responsible for the movement of bones in the La Brea tar seeps.

A wide variety of sub-ripple-scale sedimentary surface textures are known from bedding planes in the sedimentary rock record. Many of these textures were traditionally ascribed an abiotic origin (e.g., due to rain drop impact, adhesion, etc.), but in recent decades the role of microbial mats and biofilms in sculpting and mediating some forms has become increasingly recognized. Microbial sedimentary textures are now well-described and understood from modern tidal environments and biological soil crusts, but descriptions from fluvial settings are less common, despite their known occurrence in ancient alluvium. This paper reports a suite of primary sedimentary surface textures which were observed forming in discrete bodies of standing water in the lower reaches of the ephemeral Murchison River, Western Australia. Microbial sedimentary signatures included bubble impressions (burst and intact) and roll-ups, in addition to reduced horizons. Many of these features exhibited rapid temporal evolution of their morphology in the dry days following an interval of heavy rain. Significantly, these microbial features were witnessed in close spatial proximity to other abiotic and biotic sedimentary surface textures including raindrop impressions, adhesion marks, desiccation cracks, and vertebrate and invertebrate traces. Such proximity of abiotic and microbial sedimentary surface textures is rarely reported from bedding planes in the rock record, but these modern observations emphasize the fact that, particularly in non-marine environments, such structures should not be expected to be mutually exclusive. An appreciation of the fact that primary sedimentary surface textures such as these develop during intervals of stasis in a sedimentation system is crucial to our understanding of their significance and diversity in the rock record.

The dependence of skeletal alteration on time spent in the taphonomic active zone (TAZ) can generate a taphonomic clock, which can be used to quantify scales of time averaging and rates of skeletal production and recycling in the fossil record. However, the strength of the taphonomic clock is variable in present-day shallow marine environments and it is unclear how this strength varies with depth. Here, we assess the strength of the taphonomic clock in Nautilus macromphalus dead shells that were collected in cool-water, sediment-starved, epi- and mesobathyal environments off New Caledonia and range in postmortem age from few decades to several millennia. We find that, first, differences in the onset and extent of alteration states in the epibathyal zone (< 750 m) segregate well-preserved shells with red stripes (less than ∼ 200 years) from encrusted shells with faded colors and extensively bored by sponges (∼ 400 years), and from strongly fragmented, bored, and coated shell relicts (> 1,000 years). The onset of dissolution and formation of clay-goethitic coating occurs earlier (∼ 200 years) in the mesobathyal zone (> 750 m) than in the epibathyal zone. Clay-goethitic rims and boring infills show signs of microbial binding, pelletization, and coccolith dissolution and can represent nascent stages of glauconitization. Second, shells several centuries old show differences between right and left flanks (1) in the degree of encrustation and sponge bioerosion in the epibathyal zone and (2) in the extent of clay-goethitic coating in the mesobathyal zone. The upper flanks are ultimately removed in both depth zones, leaving relict half-shells that are millennia old. Third, the depth dependence of alteration can reflect a bathymetric decline in disintegration rates by heterotrophic borers due to a reduced productivity in the mesobathyal zone and an increase in dissolution rates due to the proximity of the aragonite compensation depth. The between-flank asymmetry in preservation implies (1) horizontal position of shells close to the sediment-water interface for several decades or centuries without being overturned or subjected to reworking and (2) shell exposure to two distinct taphonomic regimes separated by few centimeters, with the upper flank located in the TAZ and the lower flank facing a less aggressive sediment zone. The stable exposure of shells in the taphonomic active zone and slow alteration rates in bathyal environments allow discriminating between within-habitat time-averaged assemblages on one hand and environmentally or stratigraphically condensed assemblages on the other hand.

Ammonoid soft tissues are rarely preserved and such findings are of considerable interest. Extremely little is known about the structure of ammonoid siphuncle soft-parts. Until now indisputable fossilized siphuncle soft tissues were known only in a few ammonoid genera. This article describes phosphatized soft tissues inside the siphuncle tubes of the Upper Jurassic (upper Volgian) ammonite Kachpurites fulgens from Central Russia. Cross-sectional views of several Kachpurites siphuncles show a large blood vessel in the center surrounded by four smaller ones. In several specimens, the siphuncle epithelium is preserved. The size and arrangement of the blood vessels in Kachpurites is nearly identical to previously described blood vessels in the siphuncles of Recent Nautilus and the Permian prolecanitid ammonoid Akmilleria electraensis. This similarity indicates a remarkable conservatism of ammonoid siphuncles and provides grounds for the assumption that the last common ancestors of Ammonoidea and Nautilida also had the same structure of the siphuncle soft tissues.

Rare symbiotic rugose corals in tabulates occur in the lower Rhuddanian strata of Estonia. Thirteen out of 1115 coralla of early Rhuddanian tabulate corals of Estonia and two out of 353 coralla of Sheinwoodian tabulate corals of Gotland and Estonia contain rugose coral endobionts. Endobiotic rugose corals occur in Paleofavosites balticus (Linnaeus 1767), Paleofavosites sp., Mcleodea sp., Heliolites interstinctus (Linnaeus 1767), and Catenipora gotlandica (Yabe 1915). Endobiotic rugose corals include Tryplasma sp., Helicelasma sp., Streptelasma estonica Dybowski 1873, Streptelasma sp., Kodonophyllum cf. tubaeformis Kaljo 1957, and Palaeophyllum? sp. The latter rugose corals commonly occur independently from tabulates in the early Silurian of Estonia. It is most likely that symbiosis between rugose corals and tabulates was not obligate, but facultative. Symbiotic rugose corals presumably benefitted from growth within a stable (positionally) substrate. Rugose corals seem to have no strong negative effect on the growth of tabulates.

A Lagerstätte of Glyptocrinus decadactylus collected from the Upper Fairview Formation at Maysville, Kentucky, USA, yields new insights into the paleoautecology of camerate crinoids of the Late Ordovician. The Lagerstätte represents an autochthonous community composed of a single siltstone bed representing an obrution event and containing over 400 individual glyptocrinids that had colonized a slight topographic rise of relatively high energy within the deep subtidal zone. The high density of the crinoid community was accommodated by tiering, in which the crinoids presumably employed macroalgae (not preserved), occasionally bryozoans, and the columns of earlier-settled specimens as attachment sites; differing column lengths positioned the crinoids at various levels within the community. A further strategy for crowded conditions may have been small body size. Storm-induced turbidity flows led to the suspension of silts by a lofting plume that smothered the crinoids in their habitat. The densely packed crinoid-macroalgae assemblage may have baffled the sediment plume and induced deposition, facilitating burial. Some specimens apparently died shortly prior to burial, suggesting more than one earlier killing event, likely related to the storm that ultimately caused the obrution. Other specimens were killed by the obrution event and subjected to little or no subsequent scavenging or decay after burial, leading to excellent preservation.

The Ediacara Member of the Rawnsley Quartzite of South Australia hosts some of the most ecologically and taxonomically diverse fossil assemblages of the eponymous Ediacara Biota—Earth's earliest fossil record of communities comprised of macroscopic, complex, multicellular organisms. At the National Heritage Site, Nilpena, fifteen years of systematic excavation and reassembly of bedding planes has resulted in reconstruction of over 400 square meters of Ediacaran seafloor, permitting detailed and sequential sedimentary, paleoecological and taphonomic assessment of Ediacara fossilized communities and the shallow marine settings in which these ecosystems lived. Sedimentological investigation reveals that the Ediacara Member consists of successions of sandstone event beds and a paucity of other lithologies. Moreover, these Ediacara sandstones are characterized by a suite of sedimentary features and style of stratigraphic packaging uncharacteristic of Phanerozoic sandstone successions considered to have been deposited in analogous shallow marine, storm-dominated environments, including: (1) extremely thin (sub-mm- to mm-scale) bed thickness; (2) lateral discontinuity; (3) textural uniformity, including lack of disparity in grain size, between adjacent beds; (4) lack of amalgamation; (5) lack of erosional bed junctions; (6) doubly rippled bedforms defined by rippled bed tops and bases which crisply cast the tops of underlying rippled beds; (7) ubiquity of textured organic surfaces (TOS); (8) positive correlation between body fossil size and abundance and bed thickness; and (9) texturally immature assemblages of sandstone rip-up clasts along bed tops. We interpret these features to reflect the presence of widespread matgrounds, which facilitated seafloor colonization by and ecological development of Ediacara macroorganisms in high-energy environments. Further, we argue that pervasive matgrounds directly mediated the formation and preservation of non-uniformitarian sedimentary features and stratigraphic packaging in the Ediacara Member and were responsible for the anactualistically complete nature of the Ediacara stratigraphic record.