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The Late Devonian was a time of dramatic environmental perturbations affecting marine ecosystems. Both the Kellwasser (latest Frasnian) and the Hangenberg crises (latest Famennian) are primarily reported as phases of drastic decreases in marine diversity while the Hangenberg Crisis is also described as a bottleneck in vertebrate evolution. Fossil-bearing localities with Upper Devonian strata are of great interest to assess variations in the effects of environmental perturbations on biodiversity. For this purpose, we examined changes in alpha diversity and ecospace utilization of 21 Famennian (Late Devonian) and early Tournaisian (Early Carboniferous) invertebrate associations containing 9828 specimens from Madene el Mrakib and Aguelmous (southern Maider Basin, northeastern Anti-Atlas, Morocco), where some layers yield exceptionally preserved gnathostome remains. Both the invertebrate and vertebrate associations contain predominantly opportunistic and pelagic taxa indicating oxygen depletion near the seafloor in this region. Nevertheless, the ecospace extension was fluctuating and correlated with regional and/or global sea-level changes and oxygenation of bottom waters. In the Maider Basin, the ecospace was depleted after and during several bio-events such as the Kellwasser and Hangenberg crises, the Annulata event (middle Famennian) as well as during the early Tournaisian. Abiotic as well as biotic changes (instability of the invertebrate ecosystem) are considered to have influenced Famennian vertebrate diversity because they were more or less directly dependent on invertebrates as a food source.

Coprolites (fossil feces) provide important paleoecological information, such as diet of the producer, parasite infestation and gut microbiota, which cannot be accessed through body remains. The Upper Miocene Urumaco Formation, in western Venezuela, has a diverse vertebrate fauna composed of ground sloths, rodents, reptiles, fishes and amphibians, as well as coprolites. Here we describe 106 coprolites produced by a range of carnivorous and herbivorous vertebrates, classified into five different morphotypes based on their size and shape, suggesting different producers. Herbivorous morphotypes (M1, M2 and M5) are the most abundant (59%). The most common inclusions in these coprolites are Poaceae remains, although Eudicotyledoneae fragments, bacteria and cyanobacteria filaments were also found. The M1 morphotype has a bullet shape with longitudinal grooves; the M2 morphotype is rounded to oval, with at least one distinctive tapered end; and the M5 morphotype is a short cylinder with a rough surface, and rounded ends. In contrast, the morphotypes M3 and M4 are attributed by us to carnivores and have different inclusions. While M3 is a large cylinder with rounded ends and contains bacteria, nematode eggs and phytoliths, M4 is sausage-shaped and has muscle cells preserved inside. Based on the co-occurring fauna and the morphology of the coprolites, the probable producers were inferred as the following: M1, a rodent; M2, a notoungulate; M3, a crocodilian; M4, an indeterminate carnivore; and M5, a sirenian. The preservation of herbivorous and carnivorous coprolites with bacterial, parasitological and muscle remains in the same formation and even the same outcrop is rare in the geological record. This unique association and preservation suggests early lithification promoted by rapid burial, although the presence of the boring trace Gastrochaenolites in a single specimen indicates some degree of time-averaging.

The end-Permian mass extinction was the most severe biotic crisis in Earth's history. In its direct aftermath microbial communities colonized some of the space left vacant after the severe decline of skeletal metazoans. The Permian-Triassic boundary microbialites were peculiarly abundant on low-latitude shallow-marine carbonate shelves of central Tethyan continents. Armenia features particularly well preserved and diverse basal Triassic sponge-microbial build-ups (BTSMBs), which were not studied in detail to date. Here, the Chanakhchi section in southern Armenia is described petrographically and by means of stable isotope analyses. The Armenian BTSMBs formed in a distally open marine setting on a pelagic carbonate ramp in the course of two phases of microbial growth during the Induan (Lower Triassic). The BTSMBs are represented by predominantly thrombolitic but also dendrolitic and digitate stromatolite biostromes and mounds that vary in height between 5 cm to 12 m. The digitate stromatolites are associated with calcium carbonate crystal fans (CCFs). Microfacies analyses revealed that the BTSMBs exhibit a number of different growth forms and internal fabrics. The formation of CCFs was apparently not devoid of biological influence and took place above the sediment surface. The abundance of sponges in the BTSMBs reveals that ecologically complex metazoan-microbial reefs have been present already early after the end-Permian mass extinction. However, the formation of biostromes and mounds did not depend on sponges or other metazoans. BTSMBs that formed during the second microbial growth phase revealed similar δ13C-values like the surrounding sediment. In contrast, the δ13Cmicrobialite and δ13Csediment values from the BTSMBs and CCFs of the first growth phase show a difference of up to + 2.3‰, suggesting a significant influence of photoautotrophy during microbially induced carbonate precipitation.

The oxygen and strontium isotopic composition of 125 teeth of the hybodont sharks Lissodus and Hybodus from various late Triassic (Rhaetian) bone bed localities in the Central European Basin are used as environmental and ecological tracers for the shallow epicontinental Rhaetian Sea. The preservation of tooth enameloid was ascertained by cathodoluminescence microscopy. Mean δ18OP values differ regionally across the Rhaetian Sea with values of 18.6 ± 0.6‰ near the western gate, 16.1 ± 0.8‰ in the east, 15.4 ± 0.6‰ in the southeast, and 17.7 ± 0.9‰ in the south. The δ18OP values in the eastern Rhaetian Sea are 4–5‰ lower relative to Tethyan seawater, while teeth from the southern and western parts close to the marine gates are less fractionated. The strontium isotopic composition of teeth from most localities is more radiogenic in comparison to late Triassic seawater. The observed spatial δ18OP trend in the Rhaetian Sea indicates a shift from marine to brackish conditions in the south and west towards extensively brackish conditions with salinities of less than 16‰ in the east, thus confirming the existence of two marine gates. Brackish conditions persisted throughout early Rhaetian times, and were maintained by increased fluvial discharge from the Vindelician–Bohemian and Fennoscandian Highs as a result of enhanced atmospheric moisture availability in the course of the Rhaetian transgression. The δ18OP values of Lissodus and Hybodus indicate euryhaline behaviour of Rhaetian hybodonts by exceeding modern shark intraspecific variability. The lack of accordance in δ18OP values between different isotopically conspicuous localities in the Rhaetian Sea contradicts a basin-wide migration pattern. Differences between co-site taxa might indicate some degree of niche partitioning.

This paper presents the first quantitative study of the Early Jurassic recovery of ammonoids after the end-Triassic mass extinction based on detailed U–Pb ID-TIMS (isotope dilution thermal ionization mass spectrometry) geochronology from ash bed zircons placed within a clear phylogenetical and biochronological framework at the subzonal and species level. This study was triggered by the discovery of a rich Peruvian succession of ammonites, deposited concomitantly with an unusually large number of ash beds. Two major phases of rediversification are observed during the Psiloceras spelae and Angulaticeras zones that correspond to positive peaks in the δ13Corg curve, providing a possible link between biodiversity and the global carbon cycle. In the case of the post-extinction recovery, the development of the earliest Hettangian ammonites occurs within the genus Psiloceras, which begins with the occurrence of P. spelae and then explodes into worldwide development of smooth psiloceratids of the Psiloceras planorbis group s.l. This rapid biodiversification likely occurred less than 100 ka after the end-Triassic crisis; the genus Psiloceras occupied all the possible ecological niches worldwide, from the Pacific deep waters to the NW European shallow deposits and also in some rare Tethyan occurrences like at Germig in Tibet. This global dispersion allowed the differentiation of the group in several major phyla, the Schlotheimiidae, Discamphiceratinae, Arietitidae and Lytocerataceae, which were the roots of all other Jurassic and Cretaceous ammonites.

The thermally altered but otherwise well preserved Early Triassic palynomorphs from the Tulong area (South Tibet) allowed for qualitative and quantitative analyses and the differentiation of two distinct palynofloras, a Smithian lycopod-dominated flora and a Spathian gymnosperm-dominated flora. This suggests that gymnosperm vegetation recovered about 2 Ma after the end-Permian event on the subtropical North Indian Margin. Together with previously described successions from Pakistan, Australia, and Norway the new palynofloral record suggests an earlier establishment of diverse, gymnosperm-rich plant communities after the end-Permian event than previously proposed. The observed change in the ratio of the two major plant groups (pteridophytes/gymnosperms) in these two assemblages supports the global extent of a major climate change near the Smithian–Spathian boundary. The observed palynofloral patterns are closely related to the changes in the carbon isotope record, which suggests that the floral recovery dynamics were linked to environmental conditions.

Taphonomic models for fossil vertebrates are designed to reconstruct processes that affected carcasses during the transition from biosphere to geosphere, in particular in the interval between death and burial. To circumvent various limitations in existing methodologies, a new taphonomic method, assessing vertebrate skeletons as nine anatomical units (the head, neck, dorsal, tail, ribs and four limbs) scored independently for two characters (articulation and completeness), was developed. The potential of the method is demonstrated using the Triassic marine reptile Serpianosaurus from Monte San Giorgio, Switzerland. Specimens are preserved in alternations of black shale and dolomite, representing normal background sediment and event beds respectively, deposited into a shallow, intra-platform basin. All specimens exhibit disarticulation of skeletal elements though loss of completeness varies considerably. Minor loss of fidelity occurred during the ‘floating phase’, but individuals reached the sediment-water interface relatively soon after death, and largely intact, where they decayed during the ‘residence phase’. Carcasses allowed to reach extensive states of decay became prone to the effects of weak bottom currents, resulting in removal of elements. The episodic deposition of event beds rapidly buried individuals at various stages of decay, inhibiting further disarticulation and loss of completeness.

Lower to Middle Triassic ostracods from the Tulong section, south Tibet, are described here for the first time. Samples from the first two stages of the Early Triassic (Griesbachian and Dienerian) are barren of ostracods; the following stage (Smithian) revealed low diversity ostracod faunas; a substantial diversification in taxa began at the base of the fourth stage (Spathian) and developed into the first stage of the Middle Triassic (Anisian). Furthermore, exploration of additional feeding modes is developed in the Spathian and Anisian, with notable occurrence of filter-feeding taxa. High abundance of filter-feeding ostracods in Spathian and lower Anisian units indicates that benthic habitats became oligotrophic. These habitats typically harbored ostracod faunas of Mesozoic affinities, suggesting that the evolutionary turnover of ostracods was fostered by the declining input of nutrients from the Spathian on. Marked faunal similarities with other Tethyan areas, mainly the northern part of Tethys, are observed during Spathian and Anisian times.

11 pages; International audience; Based on new collections of abundant and well preserved material from the Salt Range (Pakistan), Spiti (Northern India) and Tulong (South Tibet), several recent studies focused on the taxonomic revision and detailed biostratigraphy of Smithian ammonoids. In this work, biochronological data for these three welldocumented basins are analyzed by means of the Unitary Associations method, resulting in a biochronological scheme of unprecedented high-resolution for the Smithian of the Northern Indian Margin (NIM). Data for each basin are first processed separately, thus yielding three local biochronological zonations. Then, the three sequences are processed together as a regional three-section data set for the construction of an inter-basin sequence at the NIM level. The latter zonation comprises 16 Unitary Associations grouped into 13 zones for the entire Smithian. Analysis of ammonoid diversity dynamics based on this new highly resolved time frame highlights (i) a marked diversification during the early Smithian, (ii) a severe extinction during the late Smithian, and (iii) an overall very high turnover throughout the Smithian. At a global spatial scale and stage resolution, the diversity of Smithian ammonoid genera appears surprisingly high, as highlighted by a previous study. It is shown that at a smaller geographic scale and with the most highly resolved time frame, Smithian ammonoids of the NIM reached their explosive diversity peak essentially through extremely high turnover rates rather than through a classic diversification process of high origination rates coupled with low extinction rates. Based on recently published U/Pb ages, regional apparent total rates of origination and extinction of more than 100 species per My can be inferred for the Smithian ammonoids of the NIM.

Few fossil vertebrate skeletons are complete and fully articulated. Various taphonomic processes reduce the skeletal fidelity of decaying carcasses, the effects of most of which are reasonably well understood. Some fossil vertebrates, however, exhibit patterns of disarticulation and loss of completeness that are difficult to explain. Such skeletons are one of two variants. They are incomplete, often markedly so, but the preserved parts are highly articulated. Alternatively, they are complete, or nearly so, but articulation varies markedly between parts of the body. A characteristic feature is the absence of skeletal elements that, on the basis of their larger size and/or greater density, would be predicted to be present. Here we erect a model, termed “stick ‘n’ peel”, that explains how these distinctive patterns originate. The model emphasizes the role of decay products, especially fluids released from the carcass while resting on the sediment surface. These fluids permeate the sediment below and around the carcass. As a result, skeletal elements on the downward facing side of the carcass become adhered to the sediment surface, and are less likely to be remobilized as a result of current activity than others. The pattern of articulation and, especially, completeness is thus not what would be predicted on the basis of the size, shape and density of the skeletal elements. The effects of stick ‘n’ peel are difficult to predict a priori. Stick ‘n’ peel has been identified in vertebrate fossils in lacustrine and marine settings and is likely to be a common feature of the taphonomic history of many vertebrate assemblages. Specimens becoming adhered to the substrate may also explain the preservation in situ of the multi-element skeletons of invertebrates such as echinoderms, and integumentary structures such as hair and feathers in exceptionally preserved fossils.