The extant Nautilus nowadays exclusively lives in the Indo-Pacific Ocean along the slopes of coral reefs, mainly in water depths of 300–400 m. It possesses a complex gas-liquid combined system to regulate its buoyancy in the water column. After death this system is lost and the shells become either positively or negatively buoyant and float for some time or respectively sink to the seafloor where taphonomic processes strongly influence the shell’s condition. A major process in taphonomy is bioerosion. We present herein a detailed study of the influence of taphonomic pathways on bioerosion in backshore collected and deep-water dredged Nautilus shells from the New Caledonia region. Some bioerosion of Nautilus shells may take place during life but most occurs after death and deposition of the shell. The ichnocoenosis found in the shells collected in backshore settings indicates that these shells were positively buoyant after the death of the animals and were initially deposited in a nearshore environment (shallow euphotic zone III to deep euphotic zone) before they were transported ashore. Part of the deep-water dredged shells, in contrast, were initially deposited in the deep euphotic to dysphotic zone before being transported into aphotic depths. We demonstrate that bioerosion supports the reconstruction of taphonomic pathways of Nautilus shells and, following an actualistic approach, it can help to reconstruct taphonomic processes and depositional settings for fossil cephalopod shells.

Rare earth element (REE) analysis of vertebrate fossils has previously been used to answer a number of stratigraphic, taphonomic, and paleoenvironmental questions concerning the depositional environments of Cretaceous siliciclastic marine and freshwater formations. In this study, vertebrate fossils from Upper Cretaceous formations of Alabama were analyzed to determine if REE analyses could be equally effective at resolving taphonomic and paleoenvironmental questions in marine carbonate strata. Results indicate that these fossils possess unique REE signatures, although they are not as distinctive as those of siliciclastic formations. REE data can also be used, with limitations, for stratigraphic assignment of vertebrate fossils as well as indicating relative paleobathymetry. Furthermore, differences in REE signatures between certain taxonomic groups and REE concentrations in different osteological material are observed. In conclusion, findings herein indicate that REE analysis of vertebrate fossils from carbonate deposits can be effective for paleoenvironmental and regional paleogeographic studies.

A widespread marine microbialite and underlying truncation surface occur in Permian–Triassic sections of South China. We interpret the microbialite to have formed as a shallow, open-marine benthic framework stimulated by high seawater CaCO₃ saturation. The widespread distribution across platform interiors and lack of asymmetry or thickening toward platform margins is incompatible with an alternative hypothesis, that microbialite deposition was stimulated by upwelling anoxic, alkaline waters. The truncation surface beneath the microbialite is irregular with overhangs and small caverns extending up to 30 cm beneath the surface indicating a dissolutional origin. Petrographic observations refute the interpretation that strata immediately beneath the surface contain pendant cements, meniscus cements, and vadose silt. Measurements of the anisopachous fibrous cements show that thickened areas have random, not downward orientations. Pores retain the pointed geometry consistent with isopachous cement. Carbon and oxygen isotope measurements, from immediately beneath the surface, do not show a negative shift as would be expected with subaerial exposure. Also incompatible with a subaerial origin is the occurrence of only one truncation surface within a subtidal succession ~ 50 m thick below the surface and the limited vertical penetration of dissolution. The surface closely resembles a hardground containing a micritized alteration zone with stromatolites encrusted on the surface. We interpret the surface to have formed by submarine dissolution driven by a pulse of ocean acidification associated with Siberian Traps eruptions and the end-Permian extinction. After a hiatus of ~ 30–100 kyr, seafloor dissolution would have brought seawater back to saturation coupled with increased delivery of calcium to the oceans as the result of elevated continental weathering and caused a rebound in carbonate saturation and precipitation of microbialites.

We here investigate the sedimentology of the early Danian (ca. 66–64 Ma) Salamanca Formation in the north-central San Jorge Basin, southern Chubut Province, Patagonia, Argentina, in order to place the outstandingly diverse and well-preserved fossil floras it contains into specific environmental settings. These assemblages are among very few of Danian age from the entire Southern Hemisphere and thus provide critical data about geographic variation in recovery from the end-Cretaceous extinction. Understanding the depositional context of the Salamanca floras is necessary for comparison with other assemblages and for interpreting their exceptional preservation. The Salamanca Formation was deposited above a widespread erosional sequence boundary (SB-1) resulting from a relative base level rise and widespread marine transgression during the early Danian (Chron C29n). In response to this increase in accommodation space, a broad, shallow estuary formed that most likely extended westward at least as far as the San Bernardo belt. A transgressive systems tract was deposited in this estuary, consisting of bioturbated sand fining upwards to silt. The maximum marine flooding surface at the beginning of the highstand systems tract is defined by well laminated, unburrowed, clay deposits of a low energy, deep shelf. The Salamanca highstand systems tract (HST) consists of sandy and silty facies capped by accreting subtidal bars and sandy shoals containing an abundance of tidal indicators, suggesting deposition proximal to the San Jorge paleo-estuary head. A second sequence boundary (SB-2), formed during Chron C28r and early C28n, separates the older highstand deposits from younger lowstand and transgressive deposits. These consist of estuarine sand shoals, trough cross-bedded sands deposited in aggrading, fluvially influenced tidal channels, tidal flat muds, and bayhead deltas. The best preservation of compression floras and petrified trees occurred near the tops of subtidal bars below SB-2; at the end of the shallowing-upward cycle that caps the second HST; and in fluvially-influenced tidal channels, tidal flat mudstones, and bayhead deltas of the lowstand and transgressive systems tracts that lie above SB-2. These settings were proximal to the source forests and had rapid rates of burial. We interpret the dark muds of the Banco Negro Inferior, which cap the Salamanca Formation, as a late transgressive and highstand systems tract deposited during a time of rising groundwater table and declining river slopes in a widespread, lowland coastal forest.

Retrodeformation of fossils can improve taxonomic and paleobiologic interpretations, but fossils that lack symmetry or other regular geometric properties are difficult to retrodeform unless strain markers are preserved within the fossil-bearing strata. Strain markers, however, are generally distributed unevenly, and their use can be problematic if strain varies among specimens and the markers do not occur in close association with the fossils. We use two approaches to retrodeform Carboniferous tetrapod tracks from the Narragansett Basin of southern New England: (1) a direct method in which the strain ratio (R_s) is obtained from deformed raindrop imprints preserved on the same specimens as the tracks and (2) an indirect method in which the range in orientation of the bedding-cleavage intersection lineation is used as a proxy for R_s. The latter follows from a strong correlation between the range in orientation of the bedding-cleavage intersection lineation and R_s values obtained from the deformed raindrop imprints, and allows the retrodeformation of tetrapod tracks not preserved in close association with deformed raindrop imprints. Our methodology was applied to both anamniote and amniote traces and was tested by retrodeforming originally bilaterally symmetric insect traces from the same location. In all cases, the trace fossils return to their expected morphology. This work shows that deformed raindrop imprints and bedding-cleavage intersection lineation are useful strain markers for the retrodeformation of trace fossils and expands our understanding of the fossil record of early tetrapods in southern New England.

Feeding traces help to characterize trophic interactions of ancient ecosystems. In rare cases, they may also provide information that is not otherwise represented by body fossils in a particular paleoenvironment. Here, we describe a diverse suite of surficial bone modifications preserved on dyrosaurid crocodyliform bones. These new fossils come from extensive Upper Cretaceous (Maastrichtian) bone and coprolite-dominated phosphate conglomerates from deposits of the Trans-Saharan Seaway in northern Mali. Five specimens have bite traces indicative of feeding by at least two species of neoselachian sharks. Features of some traces suggest they were not made in a fatal attack, but after the dyrosaurids had died, and therefore represent instances of scavenging. Other traces may be attributed to predation or early scavenging. In addition to the shark bite traces, one specimen bears minute, crescent-shaped traces that we tentatively attribute to invertebrate activity. Importantly, the traces described here document the presence of species for which body fossils have not yet been discovered.