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The Astartidae (Bivalvia) are a common benthic fossil in the British Lower Jurassic and as such it is important to understand their taxonomy so as to use them as a study system with which to consider environmental change through, and extinction events in, this epoch. The majority of the species of the Astartidae from the British Lower Jurassic are taxa within the subfamily Astartinae, encompassing the genera Neocrassina, Coelastarte and Oxyeurax. There has been some question as to whether those shells attributed to Neocrassina could be further split, with two species assigned to this genus having some characters that are atypical. We prefer to retain the atypical species within ? Neocrassina , the genus with which they have the greatest affinity, rather than erect another genus. This study assigns the suite of British Lower Jurassic fossil bivalves attributed to Nicaniella to Oxyeurax , based on the presence of a poorly defined 3a tooth and form of commarginal ridge ornament. Differentiation at the species level in Astartinae is complicated; the subfamily exhibits generally low disparity compared with other bivalves, compounded by ecomorphological effects and, in some cases, sexual dimorphism. We show that the Neocrassina lineage exhibits gradual changes in shape, as well as hinge plate development and complexity, through the Lower Jurassic, and identify potential sexual dimorphism in species of Oxyeurax. The temporally overlapping species of Oxyeurax display varying degrees of ornamental development which may well be environmentally controlled and are used in this study to define distinct new species. This study recognizes 12 distinct species of Astartinae from the British Lower Jurassic. Nine are established taxa (Neocrassina elegans, N. expansa, N. gueuxii, N. lurida, N. phaedra , ? N. camertonensis , ? N. dentilabrum, Oxyeurax duplicata, O. striatosulcata), whilstthree are new species (Coelastarte wardenensis, O. mickletonensis and Oxyeurax thompsoni). Only two of the British Lower Jurassic Astartinae species appear to have survived the global Early Toarcian extinction event as represented in British successions; one Neocrassina and one Oxyeurax. However, the lack of fossiliferous, high energy near shore environments in the early Toarcian may bias this observation, especially for Oxyeurax. [ABSTRACT FROM AUTHOR]

Upper Cretaceous ammonites are described from six horizons in the mammal-bearing terrigenous-clastic sequences of western Uzbekistan, as follows: Upper Cenomanian, with Placenticeras sp. juv. cf. cumminsi Cragin, 1893 and Metoicoceras geslinianum (d'Orbigny, 1850); Lower Turonian with Tragodesmoceras cf. mauryae Kennedy and Wright, 1981, Placenticeras kharesmense (Lahusen, 1884), Watinoceras coloradoense (Henderson, 1908), Watinoceras amudariense (Arkhangelsky, 1916b), Metasigaloceras rusticum (J. Sowerby, 1823), Morrowites wingi (Morrow, 1935), Sciponoceras cf. bohemicum bohemicum (Fritsch, 1872), and Yezoites amudariensis (Arkhangelsky, 1916b); Middle Turonian with Collignoniceras woollgari woollgari (Mantell, 1822); Upper Turonian with Lewesiceras mantelli (Wright and Wright, 1951) and Placenticeras crassum Ilyin, 2020; a single Placenticeras semiornatum (d'Orbigny, 1850) from around the Coniacian/Santonian boundary, and Santonian Placenticeras polyopsis (Dujardin, 1837). [ABSTRACT FROM AUTHOR]

The majority of species of the Arcoidea identified from the British Lower Jurassic are taxa within the Grammatodontinae. Although this study has further partitioned the Grammatodontinae fossils into the genera Grammatodon, Cosmetodon and Catella based on distinct defining characters, it is clear that differentiation at a species level becomes problematic as adults exhibit characters that grade between two distinct end states. Additionally, there is variability in characters between the juvenile and adult shells within species and the two valves of individuals. These factors have led to an over-splitting of British Lower Jurassic arcoid species, with implications in the study of marine environmental change and extinction events. After revision of the taxonomy of Lower Jurassic Arcoidea, it is clear that there was a gradual change in arcoid form through this epoch, moving from sulcate Cosmetodon to sulcate-free Grammatodon s.s. Arcoid species that survived the Toarcian extinction event in the UK were non-sulcate. This study concurs with previous research suggesting the Parallelodontidae, via the Grammatodontinae, led to the Cucullaeidae. Indeed, hinge dentition and ligament area gradational end states of some British Late Jurassic Grammatodon appear very Cucullaea-like. Dynamic environmental conditions through the Early Jurassic appear to have helped drive this evolutionary change. [ABSTRACT FROM AUTHOR]

Organised mineralised structures observed in large inoceramids (valves on a metre scale) from the Late Albian, Toolebuc Formation, Australia ( Inoceramus sutherlandi Mc Coy, 1865), and the Santonian, Niobrara Formation, USA ( Platyceramus sp.), were investigated using variable pressure scanning electron microscope ( SEM) with energy-dispersive X-ray spectroscopy ( EDX), X-ray microcomputed tomography (micro- CT) and X-ray diffraction ( XRD) analyses. These indicate that the structures comprised a phosphate framework of aligned tubes and shallow troughs overlain perpendicularly by evenly spaced structures. In the Toolebuc Inoceramus, these are U-shaped cross-structures, whilst in the Niobrara Platyceramus, they comprise bundled fibre elements. Comparison with modern bivalves indicates that the observed phosphatised structures represent soft-tissue preservation of the gills, as suggested in earlier publications. The tubes and troughs are remnants of a filamental support framework comprising ordinary and primary filaments, whilst the U-shaped cross-structures ( I. sutherlandi) and fibrous bands ( Platyceramus) represent preserved longitudinal gill musculature. Internal perforate and strand-like fabric observed on the internal surface of some Platyceramus tubular structures suggests that the framework comprised collagen. The presence of primary and ordinary filaments in numerous unusually large plicae, in at least two lamellae, indicates that the gill structures were heterorhabdic. Each plica has at least 40 ordinary filaments, an exceptional number when compared with the maximum of 20 present in modern heterorhabdic gills. The absence of incontrovertible interfilament junctions makes it difficult to say whether inoceramids were filibranch, pseudolamellibranch or eulamellibranch. However, structures that are best attributed to intraplical junctions between filaments suggest the Inoceramidae had gills akin to those of pseudolamellibranch bivalves, although their unusually large number of filaments per plica is more reminiscent of homorhabdic eulamellibranch gills. The general form of the gill is similar to that described in some other pteriomorphs, most specifically Pteria. However, it has more complex junctions and interconnections, although these are not as intricate or pervasive as those observed in the pseudolamellibranch Ostreidae. The connections and well-developed filament framework allowed the gill to reach its unusually large size, supporting the large size of these inoceramid species. The unusually large size of the gill and its components indicate that the organism fed on the larger suspended organic particles in the water column. It would also have been capable of processing large volumes of water quickly, leading to greater potential for food accumulation and with likely implications for respiratory efficiency. This may help explain the common association of inoceramids with oxygen-deficient palaeoenvironments, particularly as the general structure of the inoceramid gill is very different to that observed in the commonest extant chemosymbiotic bivalves. [ABSTRACT FROM AUTHOR]