The end-Triassic mass extinction (ETME) was one of the most severe biotic crises of the Phanerozoic, driven by environmental changes linked to Central Atlantic Magmatic Province volcanism. While the ETME is a well-studied event, its expression in organic-walled phytoplankton, particularly acritarchs, remains relatively unexplored. Palynological analysis of the Prees 2 borehole, NW England (West Midlands), spanning from the upper Rhaetian to the lower Sinemurian, reveals exceptionally diverse aquatic palynomorph assemblages. The aquatic palynological assemblages, in the context of ammonite, miospore and lithostratigraphic data, show how phytoplankton communities responded to stress and subsequent stabilization. In the upper Rhaetian, the dominance of xerophytic coniferous pollen reflects warm, semi-arid palaeoenvironmental conditions, while euryhaline palynomorphs are in a nearshore environment. Subsequent phases show increased terrestrial humidity as evidenced by the palynoflora, coinciding with reduced aquatic diversity in an assemblage adapted to low-oxygen conditions. The base of the Hettangian is marked by sustained Cheirolepidiaceae dominance and a transition from short-spined Micrhystridid occurrences (reflecting low-oxygen conditions) progressing to an increased aquatic morphological diversity phase. This latter phase includes alterations in acritarch assemblages and the proliferation of dinoflagellate cysts, indicating a shift from a proximal shallow-water to a shelf palaeoenvironmental setting. Our findings demonstrate that acritarchs are valuable indicators of palaeoenvironmental change, capturing transient ‘bloom’ phases linked to post-extinction instability and offering new insights into Early Jurassic palaeoecology and recovery following the ETME.

We report the first Hettangian theropod tracksite (~200 Ma) yielding a rich accumulation of plant remains from the Bleymard Strait (southern France). It constitutes an excellent opportunity to reconstruct lowermost Jurassic ecosystems hosting dinosaurs and which are still poorly documented in this area. Two morphotypes of tridactyl tracks are distinguished. They share similarities with Grallator and Kayentapus. Plant-bearing beds yield abundant leafy axes (Pagiophyllum peregrinum), male cones (Classostrobus sp.), wood (Brachyoxylon sp.) and pollen of conifers (Classopollis classoides). Sedimentological, petrological and mineralogical analyses demonstrated that, in the Dolomitic Formation from Bleymard, the palaeoenvironment progressively evolved from (1) a shoreface to a foreshore domain; to (2) a shallow environment that is restricted or occasionally open to the sea; then to (3) an intertidal to supratidal zone. The Hettangian theropod ecosystem of the Bleymard Strait was composed of tidal flats that were periodically emerged and bordered paralic environments inhabited by a littoral conifer-dominated forest in which Cheirolepidiaceae were the main component. The paucity of the palaeobotanical assemblage, as well as the xerophytic characteristics of Pagiophyllum, show that flora from Bleymard was adapted to withstand intense sunlight and coastal environments exposed to desiccant conditions coupled with salty sea spray, and dry conditions. These features are those of a conifer-dominated flora under a tropical to subtropical climate. The flora as well as the clay mineral analyses suggest contrasting seasons (cyclically dry then humid). This study supports that theropods were abundant and particularly adapted to this type of littoral environment bordering Cheirolepidiaceae-dominated forests.

Horseshoe crabs within Austrolimulidae represent the extreme limits to which the xiphosurid Bauplan could be modified. Recent interest in this group has uncovered an unprecedented diversity of these odd-ball xiphosurids and led to suggestions that Austrolimulidae arose during the Permian Period and had become extinct by the end of the Triassic Period. Here, we extend the temporal record of Austrolimulidae by documenting a new horseshoe crab from the Lower Jurassic (Hettangian) Bayreuth Formation, Franconiolimulus pochankei gen. et sp. nov. The novel specimen displays hypertrophied genal spines, a key feature indicative of Austrolimulidae, but does not show as prominent accentuation or reduction of other exoskeletal sections. In considering the interesting family, we explore the possible origins and explanations for the bizarre morphologies exhibited by the Austrolimulidae and present hypotheses regarding the extinction of the group. Further examination of horseshoe crab fossils with unique features will undoubtedly continue to increase the diversity and disparity of these curious xiphosurids.

A recent excavation yielded 118 large tridactyl footprints in the Lower Jurassic Dolomitic Formation of the Causses Basin, at Mongisty in southern France. Most of the tracks are ascribed to Eubrontes giganteus Hitchcock, 1845. They are preserved on a surface of 53 m2 and form parallel rows with a preferential orientation towards the north. Such an abundance and density of E. giganteus is observed for the first time in the Early Jurassic from the Causses Basin. Sedimentological and ichnotaphonomical analyses show that the footprints were made at different time intervals, thus excluding the passage of a large group. In contrast to all other tracksites from the Dolomitic Formation, where tracks are preserved in fine-grained sediments corresponding to low-energy depositional palaeoenvironments, the tracks from Mongisty are preserved in coarse-grained sediment which is a matrix- to clast-supported breccia. Clasts consist of angular to sub-rounded, millimetric to centimetric-scale (up to 2 cm), poorly sorted, randomly oriented, homogeneous dolostone intraclasts floating in a dolomudstone matrix. Sedimentological analysis shows that the depositional environments of Mongisty varied from subtidal to intertidal/supratidal settings in a large and protected flat marsh. The lithology of the track-bearing surfaces indicates that the mudflat of the Causses Basin was sporadically affected by large mud flows that reworked and redeposited mudstone intraclasts coming from the erosion of upstream, dry and partially lithified mud beds. Throughout the world, this type of preservation of dinosaur tracks in tidal matrix- to clast-supported breccias remains rare.

The lithostratigraphic characteristics of the iconic Blue Lias Formation of southern Britain are influenced by sedimentation rates and stratigraphic gaps. Evidence for regular sedimentary cycles is reassessed using logs of magnetic susceptibility from four sites as an inverse proxy for carbonate content. Standard spectral analysis, including allowing for false discovery rates, demonstrates several scales of regular cyclicity in depth. Bayesian probability spectra provide independent confirmation of at least one scale of regular cyclicity at all sites. The frequency ratios between the different scales of cyclicity are consistent with astronomical forcing of climate at the periods of the short eccentricity, obliquity and precession cycles. Using local tuned time scales, 62 ammonite biohorizons have minimum durations of 0.7 to 276 ka, with 94% of them <41 ka. The duration of the Hettangian Stage is ≥2.9 Ma according to data from the West Somerset and Devon/Dorset coasts individually, increasing to ≥3.7 Ma when combined with data from Glamorgan and Warwickshire. A composite time scale, constructed using the tuned time scales plus correlated biohorizon limits treated as time lines, allows for the integration of local stratigraphic gaps. This approach yields an improved duration for the Hettangian Stage of ≥4.1 Ma, a figure that is about twice that suggested in recent time scales.