Wealden Group Research Articles

Comptonatus chasei, a new iguanodontian dinosaur from the Lower Cretaceous Wessex Formation of the Isle of Wight, southern England

A new iguanodontian dinosaur, Comptonatus chasei gen. et sp. nov., is described from the Lower Cretaceous Wessex Formation of the Isle of Wight. These strata provide an important record of a critical time in the development of iguanodontian diversity. The specimen, which is described here for the first time, was found and excavated in 2013 and represents the most complete iguanodontian skeleton discovered in the Wealden Group for a century. A new taxon is diagnosed by several autapomorphies found in the neurocranium, teeth, coracoid and other parts of the body, together with a unique suite of characters. These include a dentary with a straight ventral border, and a markedly expanded prepubic blade. These features set it apart from the sympatric Mantellisaurus atherfieldensis, Brighstoneus simmondsi and Iguanodon cf. bernissartensis, increasing the known diversity of this clade in the Barremian–early Aptian of England. http://zoobank.org/urn:lsid:zoobank.org:pub:2F3125A5-BDEF-4835-8829-92104752A86F

A new genus of Panguoidea in Lower Cretaceous Wealden amber

ABSTRACT The panguid wasps are a ‘primitive’ family found only in the Cretaceous. Herein, a new species and genus, Protopangu valdensis gen. et sp. nov. assigned to the family Panguidae, is described and illustrated from Wealden amber, which represents one of the oldest-known fossiliferous ambers (early Barremian, ~125 Ma). A key to the genera and species of Panguidae is provided. The fossil wasp from the Wealden Group not only represents the oldest record of Panguoidea but also augments the geographic distribution of the taxon during the Cretaceous Period.

Pterosaur teeth from the Lower Cretaceous (Valanginian) Cliff End Bone Bed, Wadhurst Clay Formation, Wealden Supergroup of southern England, and their possible affinities

Until now there have been no formal descriptions of pterosaur remains from the Cliff End Bone Bed of the Lower Cretaceous (Valanginian), Wadhurst Clay Formation, Wealden Supergroup, of south-east England. This horizon yields abundant vertebrate material representing both aquatic and terrestrial taxa and recent examination of a large collection of vertebrate remains obtained by a private collector has led to the discovery of two isolated pterosaur teeth, both referable to the same taxon. Tooth crown morphology differs from that of teeth informally reported from the Wadhurst Clay Formation and attributed to ornithocheirids in being triangular in lingual and labial view, labiolingually compressed with well-defined carinae on the mesial and distal margins and with a low basal cingulum. Their possible affinities are discussed, and they are tentatively, but with some uncertainty, attributed to an istiodactylid. If this attribution is correct, they represent the earliest record of Istiodactylidae to date.

Isolated tooth reveals hidden spinosaurid dinosaur diversity in the British Wealden Supergroup (Lower Cretaceous).

Isolated spinosaurid teeth are relatively well represented in the Lower Cretaceous Wealden Supergroup of southern England, UK. Until recently it was assumed that these teeth were referable to Baryonyx, the type species (B. walkeri) and specimen of which is from the Barremian Upper Weald Clay Formation of Surrey. British spinosaurid teeth are known from formations that span much of the c. 25 Ma depositional history of the Wealden Supergroup, and recent works suggest that British spinosaurids were more taxonomically diverse than previously thought. On the basis of both arguments, it is appropriate to doubt the hypothesis that isolated teeth from outside the Upper Weald Clay Formation are referable to Baryonyx. Here, we use phylogenetic, discriminant and cluster analyses to test whether an isolated spinosaurid tooth (HASMG G369a, consisting of a crown and part of the root) from a non-Weald Clay Formation unit can be referred to Baryonyx. HASMG G369a was recovered from an uncertain Lower Cretaceous locality in East Sussex but is probably from a Valanginian exposure of the Hastings Group and among the oldest spinosaurid material known from the UK. Spinosaurid affinities are both quantitatively and qualitatively supported, and HASMG G369a does not associate with Baryonyx in any analysis. This supports recent reinterpretations of the diversity of spinosaurid in the Early Cretaceous of Britain, which appears to have been populated by multiple spinosaurid lineages in a manner comparable to coeval Iberian deposits. This work also reviews the British and global records of early spinosaurids (known mainly from dental specimens), and revisits evidence for post-Cenomanian spinosaurid persistence.

Modified skulls but conservative brains? The palaeoneurology and endocranial anatomy of baryonychine dinosaurs (Theropoda: Spinosauridae).

The digital reconstruction of neurocranial endocasts has elucidated the gross brain structure and potential ecological attributes of many fossil taxa, including Irritator, a spinosaurine spinosaurid from the "mid" Cretaceous (Aptian) of Brazil. With unexceptional hearing capabilities, this taxon was inferred to integrate rapid and controlled pitch-down movements of the head that perhaps aided in the predation of small and agile prey such as fish. However, the neuroanatomy of baryonychine spinosaurids remains to be described, and potentially informs on the condition of early spinosaurids. Using micro-computed tomographic scanning (μCT), we reconstruct the braincase endocasts of Baryonyx walkeri and Ceratosuchops inferodios from the Wealden Supergroup (Lower Cretaceous) of England. We show that the gross endocranial morphology is similar to other non-maniraptoriform theropods, and corroborates previous observations of overall endocranial conservatism amongst more basal theropods. Several differences of unknown taxonomic utility are noted between the pair. Baryonychine neurosensory capabilities include low-frequency hearing and unexceptional olfaction, whilst the differing morphology of the floccular lobe tentatively suggests less developed gaze stabilisation mechanisms relative to spinosaurines. Given the morphological similarities observed with other basal tetanurans, baryonychines likely possessed comparable behavioural sophistication, suggesting that the transition from terrestrial hypercarnivorous ancestors to semi-aquatic "generalists" during the evolution of Spinosauridae did not require substantial modification of the brain and sensory systems.

Vectipelta barretti, a new ankylosaurian dinosaur from the Lower Cretaceous Wessex Formation of the Isle of Wight, UK

The Wealden Group of southern England was deposited by rivers, on floodplains and in lagoons during the Early Cretaceous. Two historically significant ankylosaurs, Polacanthus and Hylaeosaurus, are currently known from its deposits; Hylaeosaurus from the ‘lower Wealden fauna’ and Polacanthus from the ‘upper Wealden fauna’. Here, we describe a new genus and species of ankylosaur from the Wessex Formation of the Isle of Wight, which is characterized by numerous postcranial autapomorphies. Vectipelta barretti gen. et sp. nov. is 6–8 million years older than Polacanthus, and at least 3 million years younger than Hylaeosaurus, suggesting a more complicated pattern of faunal turnover in the Wealden Group than previously realized. Vectipelta does not appear to be closely related to either of the other Wealden taxa, but instead is found in a clade with two Chinese ankylosaurs, suggesting a complex pattern of dispersal to and from Europe, North America and Asia during the Early Cretaceous. The historic practise of cataloguing all ankylosaur material from the Wessex Formation as ‘Polacanthus’ has potentially prevented a diversity of taxa from being discovered, and new and existing material in museum collections should be re-appraised using an autapomorphy-driven approach. http://zoobank.org/urn:lsid:zoobank.org:pub:0B19B56E-971D-4316-A92C-FC9AB29BBC38

Preservation of biotic and palaeoenvironmental signatures in organosulfur compounds of immature fine-grained sedimentary rocks

Organosulfur compounds (OSCs) in sedimentary rocks are considered to have formed primarily by abiotic incorporation of inorganic sulfur species into biogenetic functionalized molecules during early diagenesis, thus preserving carbon skeletons of appropriate biomolecules. OSCs could be characterized at a molecular level by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) even when they are small in amounts and large in molecular weights. Herein, to reveal the palaeoecological and palaeoenvironmental information that OSCs have recorded but might not be contained in other biomarkers, OSCs’ composition in solvent extracts of rocks with different geological histories were determined utilizing FT-ICR-MS. The analyzed natural laboratories are the marine Schöneck, Dynow and Posidonia formations and the lacustrine Wealden Formation which are in the late diagenetic or early catagenetic stages.The prevailing iron-deficient sulfidic depositional settings of the marine Posidonia and Schöneck formations are reflected by abundant OSCs bearing up to three sulfur atoms. The high ratios of reduced relative to oxidized forms (Sz versus SzOx) further illustrate the restricted presence of oxidants at the oxic-anoxic interfaces. The high average oxygen numbers of S1Ox compounds and the exclusive presence of nitrogenous OSCs (SzNy and SzNyOx) found in the marine rock extracts document the high abundances of polyoxygenated compounds and proteinaceous moieties in marine organisms that can be sulfurized. In contrast, the lacustrine organisms contain abundant sulfurizable aliphatic moieties.The observed prominent enrichment of Sz and SzOx compounds containing 40, 35, 30, 25 carbon atoms are associated with the selective and efficient preservation of polyfunctionalized biomolecules via sulfurization, such as C40 carotenoids, C35 bacteriohopanepolyols, C30 unsaturated tetracyclic polyprenoid alcohols, or C25 or C30 highly branched isoprenoid (HBI) polyenes. The strong enrichment of sulfurized C35 bacteriohopanepolyols can be developed as an indicator of the low levels of oxygen exposure prior to sulfurization, which occur only in the Dynow and Schöneck formations. The prominent enrichment of sulfurized carotenoids is generally associated with high primary productivity. While the strongly enriched sulfurized HBI polyenes in the Upper Schöneck Formation is indicative for diatom blooms, the precursors of C30 pentacyclic polyprenoid organosulfur compounds are more abundant in fresh/brackish water algae.

Microvertebrate-rich gutter casts from the basal Wessex Formation (Wealden Group, Lower Cretaceous) of Dungy Head, Dorset: Insights into the palaeoecology and palaeoenvironment of a non-marine wetland

A detailed taxonomic, taphonomic and sedimentological examination of a newly discovered microvertebrate-rich horizon within the non-marine, Lower Cretaceous Wessex Formation (Wealden Group) of Dungy Head, Dorset, aids the ecological and palaeoenvironmental reconstruction of southern England's Early Cretaceous wetlands. Historically, the Wessex Formation of Dungy Head has been neglected due to its partially vegetated state and landslipped coastal exposure; here the section's palaeontological and stratigraphical significance is realised. Non-marine, cypridoidean ostracods indicate a depositional age of late Berriasian–early Valanginian; consequently, the faunal assemblage recorded here represents the oldest fauna to be described from the Wessex Formation to date. Significantly, winnow-induced gutter casts are shown to be an important repository of mixed aquatic and terrestrial microvertebrate remains. Hydraulic sorting within a fluvial environment has resulted in the formation of multi-taxic, microvertebrate-rich gutter casts that through close lateral and stratigraphical association form a unique, bone-rich taphofacies. The recorded assemblage is typical of wetland biodiversity containing a minimum of 25 taxa including, non-marine molluscs, ostracods, elasmobranchs, osteichthyans, and tetrapods. Importantly, the gutter casts permit the taxonomic evaluation of a primarily aquatic biota in which albuliform fishes are recorded from the Wessex Formation for the first time. The biota also includes a diverse elasmobranch fauna, including hybodontoid sharks and a rhinobatid ray. Furthermore, lepidosaurs, including both scincomorphs and, tentatively, an anguimorph, are confirmed in the Wessex Formation of Dorset.

The osteology and affinities of Eotyrannus lengi, a tyrannosauroid theropod from the Wealden Supergroup of southern England.

Eotyrannus lengi Hutt et al., 2001 from the Lower Cretaceous Wessex Formation (part of the Wealden Supergroup) of the Isle of Wight, southern England, is described in detail, compared with other theropods, and evaluated in a new phylogenetic analysis. Eotyrannus is represented by a single individual that would have been c. 4.5 m long; it preserves the anterior part of the skull, a partial forelimb and pectoral girdle, various cervical, dorsal and caudal vertebrae, rib fragments, part of the ilium, and hindlimb elements excluding the femur. Lack of fusion with regard to both neurocentral and sacral sutures indicates subadult status. Eotyrannus possesses thickened, fused, pneumatic nasals with deep lateral recesses, elongate, tridactyl forelimbs and a tyrannosaurid-like scapulocoracoid. The short preantorbital ramus of the maxilla and nasals that are approximately seven times longer than they are wide show that Eotyrannus was not longirostrine. A posterodorsally inclined ridge on the ilium’s lateral surface fails to reach the dorsal margin: a configuration seen elsewhere in Juratyrant. Eotyrannus is not arctometatarsalian. Autapomorphies include the presence of curving furrows on the dentary, a block-like humeral entepicondyle, and a distoproximally aligned channel close to the distolateral border of the tibia. Within Tyrannosauroidea, E. lengi is phylogenetically intermediate between Proceratosauridae and Yutyrannus and the clade that includes Xiongguanlong, Megaraptora, Dryptosaurus and Tyrannosauridae. We do not find support for a close affinity between Eotyrannus and Juratyrant. Our analysis supports the inclusion of Megaraptora within Tyrannosauroidea and thus increases Cretaceous tyrannosauroid diversity and disparity. A proposal that Eotyrannus might belong within Megaraptora, however, is based on character states not present in the taxon. Several theropods from the Wessex Formation are based on material that overlaps with the E. lengi holotype but none can be shown to be synonymous with it.

A European giant: a large spinosaurid (Dinosauria: Theropoda) from the Vectis Formation (Wealden Group, Early Cretaceous), UK.

Postcranial elements (cervical, sacral and caudal vertebrae, as well as ilium, rib and limb bone fragments) belonging to a gigantic tetanuran theropod were recovered from the basal unit (the White Rock Sandstone equivalent) of the Vectis Formation near Compton Chine, on the southwest coast of the Isle of Wight. These remains appear to pertain to the same individual, with enormous dimensions similar to those of the Spinosaurus holotype and exceeding those of the largest European theropods previously reported. A combination of features—including the presence of spinodiapophyseal webbing on an anterior caudal vertebra—suggest that this is a member of Spinosauridae, though a lack of convincing autapomorphies precludes the identification of a new taxon. Phylogenetic analysis supports spinosaurid affinities but we were unable to determine a more precise position within the clade weak support for a position within Spinosaurinae or an early-diverging position within Spinosauridae were found in some data runs. Bioerosion in the form of curved tubes is evident on several pieces, potentially related to harvesting behaviour by coleopteran bioeroders. This is the first spinosaurid reported from the Vectis Formation and the youngest British material referred to the clade. This Vectis Formation spinosaurid is unusual in that the majority of dinosaurs from the Lower Cretaceous units of the Wealden Supergroup are from the fluviolacustrine deposits of the underlying Barremian Wessex Formation. In contrast, the lagoonal facies of the upper Barremian–lower Aptian Vectis Formation only rarely yield dinosaur material. Our conclusions are in keeping with previous studies that emphasise western Europe as a pivotal region within spinosaurid origination and diversification.

The retention of precursor biotic signatures in the organonitrogen and organooxygen compounds of immature fine-grained sedimentary rocks

To reveal the impact of biomass input (marine algae, terrestrial plants and lacustrine Botryococcus braunii) on the composition of high molecular weight organooxygen and organonitrogen compounds (Ox, Ny and NyOx), solvent extracts of immature–early mature rock and coal samples were systematically characterized by Fourier transform ion cyclotron resonance mass spectrometry using different ionization modes. In total, 16 samples from the marine Schöneck, Dynow and Posidonia formations, the lacustrine Wealden Formation and the terrestrial New Zealand coals were investigated.Coals as the in-situ deposits of terrestrial plants consist to a great degree of aromatic polyoxygenated Ox and N1Ox compounds, representing the degradation products of lignin like phenolic ketones and carboxylic acids as well as their condensation products with the degradation intermediates of labile organonitrogen compounds. Aliphatic Ox moieties derived from plant protective constituents principally waxes and cutan show a pronounced even or odd carbon number predominance of the C23–C33 species with C26, 28, 30 or C27, 29, 31 as the major homologs. In contrast, marine and lacustrine microbial communities contribute plentiful middle-chain C22, C24 or C23, C25 Ox compounds. Marine rock extracts are characterized by abundant organonitrogen compounds, especially N2 and N2Ox classes, interpreted as signatures of protein-rich marine algae that were successfully preserved via a degradation-recondensation pathway, whereas the low protein content of lacustrine Botryococcus braunii is reflected by a low amount of N1Ox and N1 classes. Highly aliphatic algaenan of Botryococcus braunii sterically protected its oxygen-bearing groups from degradation, leading to a great abundance of Ox compounds, furthermore, it characterizes the Botryococcus braunii source by substantial heteroatomic species containing more than 40 carbon atoms.

Clay mineral formation and transformation in non-marine environments and implications for Early Cretaceous palaeoclimatic evolution: The Weald Basin, Southeast England

Analyses of clay minerals within the Early Cretaceous Weald Basin, Southeast England reveal kaolinite, illite and chlorite as the main detrital clay minerals while glauconite and smectite are subordinates. A kaolinite-rich assemblage which characterized the sand-dominated Ashdown and Tunbridge Wells Sand formations and an illite-dominated assemblage associated mostly with the Wadhurst Clay and Weald Clay formations are recognized. Kaolinite was enriched in the Ashdown and Tunbridge Wells Sand formations during warm and humid climate with high precipitation that encouraged chemical weathering and leaching, while cold and dry conditions favoured the concentration of illite in the Wadhurst Clay and Weald Clay formations. Rainfall patterns associated with warm climate were drastically reduced during the drier climatic conditions. Most clay minerals are detrital in origin, with chlorite being more prominent than previously recognized. Contrary to previous studies and assumptions, this study revealed that authigenic clay minerals are present in the Hastings Beds, with vermiform and mica-replacive kaolinite being the most common, consistent with humid depositional environments. Isolated authigenic illite is also present, along with a chloritized grain, providing evidence for mesodiagenesis. The absence of dickite and occurrence of kaolinite, suggest that authigenic illite formed in relatively shallow burial conditions, indicating a maximum burial depth of 2500 m–3000 m, about 1000 m deeper than previous estimates of 1500 m–2000 m. Authigenic clay minerals are absent in the Weald Clay Formation possibly because of hindered flow of meteoric water and limited growth space for authigenic minerals. This study is significant in: 1) reinforcing multiple methods to facilitate a robust and balanced knowledge of formation and transformation of clay minerals; 2) investigating detrital and authigenic clay mineral assemblages when assessing the palaeoenvironments of sedimentary basins.

Authigenic berthierine and incipient chloritization in shallowly buried sandstone reservoirs: Key role of the source-to-sink context

Abstract Chlorite is recognized worldwide as a key mineral that inhibits the development of quartz cement in deeply buried sandstone reservoirs. Iron-rich chlorite is mainly formed by the transformation of a precursor clay mineral; however, few studies have focused on the early stages before the crystallization of chlorite. This study analyzed shallowly buried (400–1000 m) coastal sandstones from within the Wealden Group of the Paris Basin. Berthierine, a 7 Å trioctahedral clay mineral belonging to the serpentine group, approximatively with same chemistry as chlorite but a different crystal structure, has been identified in a 900-m-deep well but not in a 400–600-m-deep well. Berthierine has mainly been observed as clay coatings around detrital grains with a typical honeycomb texture. Nanopetrographic observations suggest that the honeycomb textural organization of the clay particles found in deeper buried sandstone reservoirs (>1500 m) is acquired from a berthierine precursor at shallow depths. However, small amounts of quartz overgrowths are observed on the surface of detrital grains at shallow depths and low temperature (below 40 °C), and it is believed that precursor berthierine coatings are primarily responsible for the inhibition of quartz overgrowths before Fe-rich chlorite is formed. This suggests that the key mineral primarily controlling the reservoir quality of deeply buried sandstone reservoirs is berthierine rather than iron-rich chlorite, which challenges the commonly accepted assertion that chlorite coating is the main process that inhibits quartz overgrowths. The source-to-sink context of the Paris Basin during the Early Cretaceous was decisive with respect to the supply of sands and berthierine clay precursors (in particular kaolinite and iron-rich, hydroxy-interlayered clay minerals) to the center of the basin.

New and little known taxa of the suborder Ensifera (Insecta: Orthoptera) from the Lower Cretaceous of England

This is a continuation of the synoptic monograph of fossil Orthoptera from the English Lower Cretaceous (Purbeck and Wealden groups) published in 2006. A new species belonging to the superfamily Elcanoidea is described from the Purbeck Group: ?Sibelcana websteri sp. nov. One species of the superfamily Hagloidea from the Purbeck Group is redescribed on the basis of a much more complete imprint: Cyrtophyllites cretaceous Gorochov, Jarzembowski et Coram, 2006. Two new genera and two new species of the superfamily Grylloidea are described from the Wealden Group: Transigryllus edmundi gen. et sp. nov. and Proararipegryllus andrewi gen. et sp. nov. One species from the Wealden Group, originally included in the Brazilian Cretaceous genus Araripegryllus Martins-Neto, 1991, is here transferred to the latter new genus: Proararipegryllus orientalis (Gorochov, Jarzembowski et Coram, 2006), comb. nov.

First Stegosaurian Dinosaur remains from the Early Cretaceous of Burgos (Spain), with a review of Cretaceous stegosaurs

Stegosaurian remains from the Early Cretaceous (Wealden beds, probably Hauterivian-Barremian) of Aldea del Pinar (Burgos, Spain) are described. The material consists of the ?most posterior dorsal vertebra and a partial dermal plate. The general form of the vertebra, with a massive centrum, a prominent lateral depression and solid neural arch pedicels, is reminiscent of the dorsal vertebrae of Dacentrurus, but the centrum is even more massive than in this genus from the Late Jurassic. Pending the discovery of new fossils, the Burgos material is provisionally referred to as Stegosauria indeterminate. This is the first report of stegosaurs in the region of Castilla y León and one of the few records of this group of thyreophoran dinosaurs from the Early Cretaceous of Europe. The occurrence of other Cretaceous stegosaurs is reviewed.

A new hadrosauriform dinosaur from the Wessex Formation, Wealden Group (Early Cretaceous), of the Isle of Wight, southern England

A new genus and species of non-hadrosaurid hadrosauriform dinosaur, Brighstoneus simmondsi gen. et sp. nov., is described from the Lower Cretaceous Wessex Formation of the Isle of Wight. The new taxon has two autapomorphies, a nasal having a modest nasal bulla with convex sides, and primary and accessory ridges on the lingual aspect of the maxillary crown. The dentary has at least 28 alveolar positions, which is the highest number recorded in an ornithopod with non-parallel sided alveoli, creating a character combination that is unique within Iguanodontia. The hadrosauriform fauna of the Barremian–Aptian Wealden Group on both the Isle of Wight and mainland England has been represented for almost a century by just two taxa, the robust Iguanodon bernissartensis and the more gracile Mantellisaurus atherfieldensis, with referred material often being fragmentary or based on unassociated elements. This discovery increases the known hadrosauriform diversity in England and, together with recent discoveries in Spain, suggests that their diversity in the upper Wealden of Europe was considerably wider than initially realized. This find also has important implications for the validity of the Mantellisaurus atherfieldensis hypodigm, and a reassessment of existing material is suggested. http://zoobank.org/urn:lsid:zoobank.org:pub:31F0D48F-C1DA-406E-A811-1F5937ED19F4

Sphaerosiderites as sensitive recorders of non‐marine depositional and diagenetic history: Insights from the Lower Cretaceous Wealden Supergroup

AbstractWaterlogged, reducing soils in modern and ancient wetlands feature distinctive syndepositional to early diagenetic spherical iron carbonate concretions, known as sphaerosiderites. Sphaerosiderites are thought to record pore water elemental chemistry and local palaeoenvironmental conditions, and are widely used in palaeohydrological reconstructions throughout the Phanerozoic. The Lower Cretaceous non‐marine Wealden Supergroup of Southern England, deposited in fluvio‐lacustrine settings, contains abundant well‐preserved sphaerosiderites offering an ideal archive for unravelling the geochemistry of ancient non‐marine environments. Sphaerosiderites were characterised via multiple microanalytical techniques (SEM‐EDS, EPMA, XRD, SIMS), and show morphological and compositional heterogeneity (e.g. concentric zones of variably enriched Mn, Ca or Mg, elemental differences between cores and rims) in well‐preserved sphaerosiderites from the Ashdown and Tunbridge Wells Sand formations. The preservation of primary fabrics, lack of post‐burial cements or extensive alteration suggests these sphaerosiderites record primary palaeoenvironmental conditions. By contrast, in the Wadhurst Clay Formation, sphaerosiderites are recrystallised, potentially reflecting wide scale palaeoenvironmental changes (e.g. marine incursions). New experimental constraints on elemental uptake during siderite growth suggests that rather than reflecting pore water elemental chemistry, the elemental heterogeneity in the Wealden sphaerosiderites reflects complex parameters; variations in pH, cation concentrations, DIC, growth rate and siderite saturation state in groundwaters. At a larger scale, morphological and compositional differences between sphaerosiderites from distinct palaeosol horizons record spatial and temporal variability in local hydrogeochemistry. This suggests that the Weald Basin wetlands of the Lower Cretaceous featured a dynamic and periodically fluctuating groundwater table, where sphaerosiderites growing close to the soil surface responded rapidly to variability in physiochemical conditions, consistent with wet and warm conditions suggested by sedimentological evidence and climate model simulations. Similar morphological and compositional variability noted in other Phanerozoic sphaerosiderites suggests analogous processes operated in ancient wetlands, and that sphaerosiderites could provide a crucial tool to understand wetland dynamics in deep time.

Provenance evolution of the English Lower Cretaceous Weald Basin and implications for palaeogeography of the northwest European massifs: constraints from heavy mineral assemblages

The first comprehensive provenance studies of the English Lower Cretaceous facies based on detailed analyses of heavy minerals is presented from 11 locations across the Weald, southeast England. These samples were subjected to QEMSCAN® analysis which provided detailed comprehensive datasets on the heavy minerals within the sediments. Four heavy mineral assemblages were identified in the Hastings Beds: rutile, olivine, tourmaline and apatite dominated assemblages in decreasing order. The Weald Clay Formation is also dominated by four heavy mineral assemblages: apatite, rutile, tourmaline and pyroxene-garnet-epidote dominated assemblages in decreasing order. The high concentrations of rutile, tourmaline and zircon in these samples show that bulk of the sediments were recycled from older sediments within the provenance and show a high degree of reworking of sediments into the basin. These provenances appeared to be primarily granitic with metamorphic interruptions at different times in the basin. Heavy minerals indicate little or no secondary modifications to the sediments. Drastic changes in the values of ZTR index suggested repeated retreat and advance of these provenances. Pearson correlation coefficients revealed that four distinct provenances (Londinia, Armorica, Cornubia and Boreal) supplied varying quantities of sediments into the basin at different times. The evolution of these four provenances revealed the complex nature of the palaeogeography of these massifs which had significant implications on other north-western European basins. The wider implication of this study shows that QEMSCAN® method can be successfully and effectively used for analysing heavy minerals for provenance studies when traditional petrographic/heavy mineral methods are not available or unreliable.

The Wessex Formation (Wealden Group, Lower Cretaceous) of Swanage Bay, southern England

The Early Cretaceous Wealden Group of Swanage Bay, Dorset, southern England, comprises two formations, a lower Wessex Formation and an overlying Vectis Formation. Presently only part of the former is exposed and here its stratigraphy, sedimentology and palaeontology are redescribed. Recent work on the Wealden Group of the Wessex Sub-basin has focused either on the Barremian – earliest Aptian of the Isle of Wight, or on the Wealden Group of Dorset in a broader context. Consequently, the Wealden Group of Swanage Bay lacks detailed analysis and description. In the 200 years since the first account of the geology and stratigraphy of Swanage Bay, slumping and vegetation growth have dramatically concealed the upper part of the Group at this previously well-known locality. A stratigraphical framework with assigned marker beds is established here for the first time allowing for the precise placement of new palaeontological discoveries. Analysis of the palaeobotanical and microvertebrate remains recovered from the recorded section permits a more accurate reconstruction of the Early Cretaceous Wessex Formation ecosystem of east Dorset.

Osteology and Taxonomy of British Wealden Supergroup (Berriasian–aptian) Ankylosaurs (Ornithischia, Ankylosauria)

ABSTRACT Ankylosaurs, dinosaurs possessing extensive body armor, were significant components of terrestrial ecosystems from the Middle Jurassic–latest Cretaceous. They diversified during the Early Cretaceous, becoming globally widespread. The Lower Cretaceous Wealden Supergroup (Berriasian–Aptian) of Britain has produced abundant ankylosaur material, with three currently recognized taxa: Hylaeosaurus armatus (Grinstead Clay Formation, West Sussex); Polacanthus foxii (Wessex Formation, Isle of Wight); and Horshamosaurus rudgwickensis (Weald Clay Group, West Sussex). However, these taxa are poorly understood; the initial descriptions of Hylaeosaurus and Polacanthus date from the 1800s and subsequent referrals of specimens have been based largely on provenance rather than morphological comparisons. This has led to uncertainty over the definitions of these taxa and the compositions of their hypodigms. Here, we redescribe the holotypes of Hylaeosaurus and Polacanthus, provide comparisons between these taxa, and use this information to assess the taxonomy of all ankylosaur specimens from the British Wealden Supergroup. We conclude that Hylaeosaurus and Polacanthus are valid, distinct taxa, which can be diagnosed by a combination of autapomorphies and a unique combination of characters. However, in both cases, we restrict their hypodigms to the holotypes. ‘Horshamosaurus rudgwickensis’ is a nomen dubium (an indeterminate nodosaurid dinosaur) and the majority of ankylosaur specimens from the Wealden Supergroup are taxonomically indeterminate. Hylaeosaurus and Polacanthus are separated stratigraphically, with Hylaeosaurus from the Valanginian of the Weald Sub-basin and Polacanthus from the Barremian of the Wessex Sub-basin. This separation supports the hypothesis of distinct lower and upper dinosaur faunas in the Wealden Supergroup of Britain.