External Mould Research Articles

Boreognathus pogorevichi , a remarkable new polychaete annelid from the lower Permian of the Pechora Basin, Russia

The sclerotized jaw elements (scolecodonts) of polychaete annelids are rarely preserved as articulated jaw apparatuses. Here we describe a morphologically unusual, rather large, and symmetrical jaw apparatus, assigned to the new taxon Boreognathus pogorevichi gen. et sp. nov., from the Kungurian (lower Permian) of the Pechora Coal Basin, northern Cis-Urals, Russia. Whereas the specimen is mainly preserved as a three-dimensional external mould of the near-complete dorsal maxillary apparatus, some organic matter comprising the original jaw wall is also retained. The new taxon combines edentate, pincer-like first maxillae (MI) typical of the extant Labidognatha apparatus type with long slender carriers common in the Prionognatha type. Unlike the smooth MI, MII are consistently and prominently denticulated. The new genus represents a hitherto unknown type of polychaete jaw apparatus and is assigned to the Palaeozoic family Atraktoprionidae.

A New Species of Ophiura (Echinodermata, Ophiuroidea) from Miocene Deep-Sea Deposits in the Pohang Basin, Korea

Dense aggregations of articulated ophiuroids, in external mould preservation, were discovered in the middle Miocene Duho Formation (Yeonil Group) of Pohang City, near the southeast coast of Korea. These specimens are here described as a new species, Ophiura pohangensis, which differs from congeners in having long, slender oral papillae, and tiny quadrangular arm comb papillae. The new species constitutes the first well-identified example of the class Ophiuroidea in the fossil record of Korea. Aggregation density of the new species is similar to that of occurrences of both fossil and extant Ophiura sarsii sarsii across Japan.

Notes on some Late Cretaceous goniasterid starfish (Echinodermata, Asteroidea) from Belgium and Germany

Both partially articulated specimens and dissociated marginal ossicles form the basis for erection of two new species of Late Cretaceous goniasterids from the Mons and Liège-Limburg basins (Belgium) and the Hannover area (Germany). Chomataster breizh sp. nov., which recalls the type species, Chomataster acules Spencer, 1913, but differs in several respects, is based on a partial external mould of the marginal frame of disc and arms in flint (upper Campanian Spiennes Chalk Formation; Mons Basin), as well as on a more or less complete individual, preserving small, spherical spines and granules and encased in a flint nodule from the upper Maastrichtian Nekum Member (Maastricht Formation; Liège-Limburg Basin). In Ch. breizh sp. nov., supero- and inferomarginals bear close-set granule pits, of varying sizes, as well as bivalved alveolar scars of pedicellariae; median superomarginals and all inferomarginals lack large, crater-shaped spine pits – such are found only in the disc/arm transition and along the arms. Dissociated supero- and inferomarginal ossicles from the lower and upper Campanian of the Hannover area and the upper Campanian of northeast Belgium, previously recorded either as indeterminate astropectinids or as Nymphaster obtusus (Forbes, 1848) var. nov. and as Nymphaster sp., respectively, here are assigned to Nymphaster mudzborgh sp. nov. This species is characterised by a row of 3–5 large spine pits on the aboral and lateral surfaces of superomarginals; inferomarginals have an angular profile and a close cover of granule pits. Nymphaster tethysiensis Villier, 2001, from the upper Campanian of Landes (southwest France; Villier and Odin, 2001) appears best accommodated in Chomataster as well, because in the arm superomarginals alternate rather than meet over the mid-radial line.

Ultrastructure and in-situ chemical characterization of intracellular granules of embryo-like fossils from the early Ediacaran Weng’an biota

Embryo-like fossils from the early Ediacaran Weng’an biota provide a window of exceptional fossil preservation onto the period of life history in which molecular clocks estimate the fundamental animal lineages to have diverged. However, their diversity and biological affinities have proven controversial, because they are morphologically simple and, consequently, their interpretation lacks phylogenetic constraint. The subcellular structures preserved in these embryo-like fossils might help to understand their cytology, biology, and diversity, but the potential of these structures has not been fully realized, because detailed microscale physical and chemical investigations are lacking. Here, to remedy this deficiency, we performed a comprehensive study to characterize their micro- and ultra-structures as well as in-situ chemical components. Our results reveal three types of subcellular structure that differ in size, shape, and mineral components: (1) relatively small and spheroidal granules in embryo-like fossils with equal cell division pattern; (2) relatively large, spheroidal, or polygonal granules in embryo-like fossils with unequal and asynchronous cell division pattern; and (3) irregular multi-layered rim-bounded granules in embryo-like fossils with unequal and asynchronous cell division pattern. We propose that the three types may be rationalized to a single taphonomic pathway of preferential mineralization of the cell cytoplasm, preserving an external mould of subcellular granules. We followed the previous interpretation that the spheroidal and polygonal granules should be fossilized lipid droplets or yolk platelets. The distinction between these subcellular structures are largely the result of postmortem degradation processes such as autolysis. The widely preserved lipid droplets or yolk platelets within these Ediacaran embryo-like fossils are compatible with the interpretion of large yolky embryos with maternal nourishment and direct development.

Systematic Revision and Palaeobiology of Emplastron edwardsi (Van Straelen, 1928) gen. et comb. nov. (Crustacea, Decapoda, Astacidae) Entombed within Travertine, from Sézanne, France

Crayfish are rare in the fossil record and therefore it is important to investigate each occurrence in detail. The only known fossil crayfish from France, Astacus edwardsi Van Straelen, 1928, is known from a replica made by pouring plaster of Paris inside the holotype (subsequently destroyed), an external mould extracted from a travertine cavity from the Thanetian of Sézanne. An evaluation of the taxonomic name, A. edwardsi, is provided; A. edwardsi is considered valid in accordance with ICZN rulings. It possesses atypical features for all other astacid genera, thus Emplastron gen. nov. is erected. Emplastron edwardsi gen. et comb. nov. inhabited a warm climate with calm waters, abundant food sources, and an ample supply of calcium carbonate: so much so that it is surprising that it is the only recovered specimen. Despite apparent North American faunal and floral affinities in the vicinity, E. edwardsi is more closely related to European crayfishes than it is to American ones.

Furongian (Jiangshanian) occurrences of radiodonts in Poland and South China and the fossil record of the Hurdiidae.

The Furongian period represents an important gap in the fossil record of most groups of non-biomineralizing organisms, owing to a scarcity of Konservat-Lagerstätten of that age. The most significant of these deposits, the Jiangshanian strata of the Sandu Formation near Guole Township (Guangxi, South China), have yielded a moderately abundant, but taxonomically diverse soft-bodied fossil assemblage, which provides rare insights into the evolution of marine life at that time. In this contribution, we report the first discovery of a radiodont fossil from the Guole Konservat-Lagerstätte. The specimen is an incomplete frontal appendage of a possibly new representative of the family Hurdiidae. It is tentatively interpreted as composed of seven podomeres, six of which bearing laminiform endites. The best preserved of these endites is especially long, and it bears short auxiliary spines that greatly vary in size. This is the second occurrence of hurdiids and more generally radiodonts in the Furongian, the first being the external mould of an oral cone from Jiangshanian strata of the Wiśniówka Sandstone Formation in Poland. Restudy of this Polish specimen confirms that it belongs to a hurdiid radiodont and best compares to Peytoia. The family Hurdiidae includes the oldest (basal Cambrian Epoch 2) and youngest (Early Ordovician, possibly Early Devonian) representatives of the Radiodonta and as such, has the longest stratigraphical range of the group. Yet, hurdiids only became prominent components of marine ecosystems during the middle Cambrian (Miaolingian), and their fossil record in younger strata remains limited.

The first report of epipunctae in non-plaesiomyid brachiopods from the lowest Silurian of southeastern China

Epipunctae are microscopic perforations that do not penetrate the shell but are confined to the outer layers of the shell. They have been known previously only in the orthidine family Plaesiomyidae. The striated walls of epipunctae are considered unique to brachiopods and thus of significance for the study of stem-group brachiopod. In this study, we report the first occurrence of epipunctae in a non-plaesiomyid brachiopod based on a well-preserved external mould of Cathaysiorthis yushanensis from the lower Silurian Shiyang Formation of Jiangxi, southeastern China. The species belongs to the Family Cathaysiorthidae which differs from the Family Plaesiomyidae in many aspects especially in dorsal internal structures. The new data imply that epipunctae may be more widespread in orthide brachiopods than previously thought, strengthening the notion that this is a plesiomorphic character of the brachiopod shell. The discovery of epipunctae, however, depends on excellent preservation of the outer surface of the shells as well as careful cleaning and observation.

Nucleus preservation in early Ediacaran Weng'an embryo-like fossils, experimental taphonomy of nuclei and implications for reading the eukaryote fossil record.

The challenge of identifying fossilized organelles has long hampered attempts to interpret the fossil record of early eukaryote evolution. We explore this challenge through experimental taphonomy of nuclei in a living eukaryote and microscale physical and chemical characterization of putative nuclei in embryo-like fossils from the early Ediacaran Weng'an Biota. The fossil nuclei exhibit diverse preservational modes that differ in shape, presence or absence of an inner body and the chemistry of the associated mineralization. The nuclei are not directly fossilized; rather, they manifest as external moulds. Experimental taphonomy of epidermal cells from the common onion (Allium cepa) demonstrates that nuclei are more decay resistant than their host cells, generally maintaining their physical dimensions for weeks to months post-mortem, though under some experimental conditions they exhibit shrinkage and/or become shrouded in microbial biofilms. The fossil and experimental evidence may be rationalized in a single taphonomic pathway of selective mineralization of the cell cytoplasm, preserving an external mould of the nucleus that is itself resistant to both decay and mineral replication. Combined, our results provide both a secure identification of the Weng'an nuclei as well as the potential of a fossil record of organelles that might help arbitrate in long-standing debates over the relative and absolute timing of the evolutionary assembly of eukaryote-grade cells.

A lower Silurian (Llandovery) diplobathrid crinoid (Camerata) from mid-Wales

AbstractEarly Palaeozoic crinoids are known only patchily from the British Isles except for accumulations at starfish beds. A single, exquisitely preserved crinoid is reported from the Telychian (Llandovery, Silurian) of the Pysgotwr Grits Formation of the Llangurig area, Powys, mid-Wales. This sedimentary succession is turbiditic in origin and poorly fossiliferous. The crinoid is a diplobathrid camerate,Euptychocrinus longipinnulussp. nov., preserved as an external mould without counterpart. It has a high, shuttlecock-like crown; a conical, unsculptured cup; low infrabasals; a pair of long, slender, feather-like arms on each ray, each bearing numerous long pinnules; and a heteromorphic column. Most previous reports of this genus have been from the Upper Ordovician – lower Silurian series of Laurentia; uncertainly, it is described from the Upper Ordovician deposits of Morocco (Gondwana).Euptychocrinus longipinnulusis the first Avalonian occurrence. The beautiful preservation of the arms, including cover plates of pinnules, contrasts with the proxistele, which is a series of ‘broken sticks’. This crinoid responded to an adverse environmental fluctuation, probably a turbidity current, by autotomizing the stem, but it was carried downslope and buried alive.

A new limulid genus from the Strelovec Formation (Middle Triassic, Anisian) of northern Slovenia

AbstractHorseshoe crabs are an archetypal chelicerate group with a fossil record extending back to Early Ordovician time. Although extensively studied, the group generally has a low diversity across the Phanerozoic Eonothem. Here, we expand the known diversity of true horseshoe crabs (Xiphosurida) by the description of a new taxon from the Middle Triassic Strelovec Formation of the Slovenian Alps. The mostly complete fossil is preserved as an external mould and assigned to the family Limulidae Zittel, 1881 asSloveniolimulus rudkini, n. gen., n. sp. The use of landmark and semilandmark geometric morphometrics is explored to corroborate the systematic palaeontology and suggests that the new genus and species are valid. We also provide the first quantitative evidence for the extensive diversity of Triassic horseshoe crabs. We suggest that Triassic horseshoe crabs likely filled many ecological niches left vacant after the end-Permian extinction.

Substrate is a poor ichnotaxobase: a new demonstration

Substrate is a poor ichnotaxobase, yet it has been widely used for distinguishing the clavate (club-shaped) borings commonly produced by bivalves. A chert nodule from the Upper Cretaceous of Morocco encloses the external mould of a clast of unknown composition (rock? wood?) which had been extensively bored, producing both small cylindrical and large clavate pits. Numerous small, short borings are referred to Oichnus isp. cf. O. simplex Bromley; Oichnus is otherwise commonly limited to shelly substrates. More significantly, the clavate borings may either be Gastrochaenolites turbinatus Kelly and Bromley, considered confined to rock and shelly substrates, or be Teredolites clavatus Leymerie, thought to be limited to wood. These borings are morphologically indistinguishable, only being differentiated by substrate, and thus, they are considered to be synonymous herein. Gastrochaenolites clavatus (Leymerie) has priority and is the type species of Teredolites Leymerie, now considered a junior synonym of Gastrochaenolites Leymerie. Thus, the clavate borings of this specimen are identified as Gastrochaenolites clavatus (Leymerie).

Revision of the Barrande's specimen "Tige d'une Cystidée indéterminée" (Cambrian, Echinodermata, Eocrinoidea)

Reexamination of the type specimen described by Barrande in 1887 as Tige d'une Cystidee indeterminee shows that this unique specimen represents an articulated but incomplete remnant of the gogiid eocrinoid Akadocrinus jani Prokop. The specimen is preserved as an external mould in shale from the mid-Cambrian Jince Formation, and comprises a proximal part of a stem associated with a slightly disarticulated distal portion of a theca, composed of over twenty polygonal plates. With the exception of the basal-most plates, all other preserved thecal plates bear ellipsoidal marginal epispires, and substantiate assignment of this specimen to the epispire-bearing phase in ontogenetic development of Akadocrinus.

Unusual soft tissue preservation in the Early Cretaceous (Aptian) crocodile cf. Susisuchus from the Crato Formation of north east Brazil

A new specimen of the neosuchian crocodylomorph, Susisuchus sp. from the Lower Cretaceous (Aptian) Crato Formation of Ceará, North East Brazil is remarkable for extensive preservation of the epidermis and limb musculature. The specimen comprises incomplete post-cranial remains, including an articulated sequence of thirteen thoracic vertebrae, a disarticulated pair of lumbar vertebrae and all four limbs articulated in varying degrees of completeness but divorced from the axial skeleton. Soft tissues are preserved in two distinct modes, in close association with the skeletal remains. An external mould of the dorsolateral scales of the trunk extends over a bedding plane surface while mineralisation of soft tissues preserving the musculature surrounds the left forelimb. Soft tissue preservation is extremely rare in crocodylomorphs and this is only the second report of soft tissue preservation in a crocodilian from the Crato Formation.

Two little-known crinoids from the type area of the Devonian, south-west England

There were few publications on the British Devonian Crinoidea between the last parts of the Reverend G.F. Whidborne’s monograph in the 1890s and 1900s and the revival of interest in these faunas in the 21st Century. The paper records two Devonian cladid crinoids collected in the 19th Century; neither was described nor illustrated hitherto. Both are in the collection of the Sedgwick Museum, Cambridge. These specimens are from the Lower Devonian (Emsian) Meadfoot Group (=‘Staddon Grits’) of New Cut, Lincombe Drive (=‘Lincombe Slates’), Torquay, south Devon. Parisocrinus? has been published in name. The cup is deformed and preserved as an internal mould; comparison with the diagnosis of the genus shows that Bather’s determination was questionable. Further, the oldest, confidently determined Parisocrinus is Middle Devonian. However, a second cladid, Vasocrinus sp., not recorded hitherto, is a partial external mould and seems to be correctly determined. A further specimen, on the same specimen board as Vasocrinus, preserves three parallel, pinnulate arms as moulds of the adoral surface; they are unlikely to be conspecific.

An enigmatic echinoid spine from south Devon, UK: Devonian or Cretaceous?

Echinoids are poorly known from the Devonian of SW England. This report records an external mould of a solitary primary spine in a chert cobble collected from near the site of Wolborough Quarry, SW Devon, a well-known Middle Devonian palaeontological site. However, cherts are rare in Devonian limestones of south Devon and the spine is unusually robust in comparison with those of other Devonian taxa. The cobble is here interpreted as an erratic, most probably an Upper Cretaceous flint, and the spine is identified as Prionocidaris sp. cf. P. vendocinensis (Agassiz & Desor). This is another illustration of the high fidelity possible in fossils preserved in cherts even after reworking.

Eocene fossil feather from King George Island, South Shetland Islands, Antarctica

AbstractThe first fossil avian feather from Antarctica is reported here, from the early to middle Eocene Fossil Hill Formation at Fildes Peninsula, King George Island, Antarctica. Characteristics such as its form, asymmetry of vanes, closed-pennaceous vanes with barbules and a deep ventral groove indicate that the feather was used for flight. The site from which the feather was collected is known to yield a variety of well-preserved trace fossils, palaeobotanical and palaeoenvironmental remains, suggesting a shorebird ecotype for the owner of this feather, certainly belonging to a Neornithes. The continental position, preservation as an external mould and type of feather makes this specimen a novel and an exceedingly rare record.

Notes on selected Cretaceous echinoids from south-central Sakhalin, Far East Russia

AbstractFrom Albian, Santonian and Campanian strata in south-central Sakhalin, four echinoid taxa are described, illustrated and discussed. In Far East Russia, echinoids are rare constituents amongst mid- and Late Cretaceous macrofaunal assemblages in which inoceramid and non-inoceramid bivalves, plus heteromorph and non-heteromorph ammonites predominate. The sole regular species in the present lot is represented by an incomplete external mould of a primary spine of a rhabdocidarid,Polycidaris(?) sp., from the lower Campanian. Irregular taxa include a fragmentary, specifically indeterminate ‘pygurid’,Echinopygus(?) sp., of late Albian age, as well as two spatangoids. One of these, a toxasterid of late Campanian age, is assigned toNiponastercf.hokkaidensis(LambertinLambert & Thiéry, 1924). The other is a new hemiasterid with a semi-ethmophract apical disc, a peripetalous fasciole with diffuse boundaries (parafasciole) and posterior petals that are near-equal in length to anterior ones, from lowermost Campanian strata. For this, the namePalhemiaster natalyaen. sp. is introduced. Comparisons with coeval echinoid faunas from nearby Hokkaido (northern Japan) are hampered by the generally poor preservation of the latter. However, with the exception ofNiponastercf.hokkaidensis, none of the forms recorded in the present paper appears to be represented in those Japanese assemblages.

Mathematical modelling of producing hollow ingot by electroslag casting with liquid metal

Electroslag casting with liquid metal (ESC LM) is a new technology in electroslag metallurgy. Solid ingot, hollow ingot and bimetal composite can be produced by the ESC LM process. Using both internal and external current carrying moulds for ESC LM is a new method for manufacturing hollow ingots. Liquid metal is employed directly during the ESC LM process rather than the conventional consumable electrode. The process was simulated using infinite element software ANSYS. The results indicate that the conductive path of the ESC LM process is entirely different from the conventional electroslag remelting process. There are two conductive current paths: one conductive path is transformer→external current conductive mould→liquid slag→internal current conductive mould→transformer, and another conductive path is transformer→external current conductive mould→liquid slag→molten steel pool→liquid slag→internal current conductive mould→transformer. Current density, magnetic inductive intensity, electromagnetic force, Joule heat distributions and fluid flow are concentrated on the upper area of the slag pool. In addition, the higher temperature region of the slag pool is at the upper area of the slag pool. The superheat of the molten steel pool is lower than the conventional electroslag remelting process, which favours improving the quality of the hollow ingot. Simulation of the ESC LM process will help understanding the process and choose better operating parameters.

The oldest azhdarchoid pterosaur from the Late Jurassic Solnhofen Limestone (Early Tithonian) of Southern Germany

Based on an almost complete three-dimensionally preserved skeleton, a new genus and species of an azhdarchoid pterosaur Aurorazhdarcho primordius n.gen. n.sp. from the Late Jurassic Solnhofen limestone (Early Tithonian) of the Eichstatt area (Bavaria, Germany) is described. Furthermore, a new family the Protazhdarchidae is proposed. The specimen is attributed to the Azhdarchoidea based on its glenoid fossa level with the sternum, the shovel-like shape of the sternal plate, the wide furca of the coracoid, the metacarpus being longer than radius and ulna, the femur being 1/3 longer than the humerus, the femorotibial ratio, and the hammer-shaped humerus among other diagnostic features. Under UV-light, soft tissue preservation around the external mould of the head is visible. It consists of tiny flakes possibly remnants of skin. The dorsally curved outline of the external mould of the head suggests the presence of a cranial crest. The new species is the oldest record of the azhdarchoid pterosaurs. It supports the Eurasian origin of this group that includes the largest flying animal ever.

Optimum shapes of scarf repairs

Adhesively bonded scarf repairs are the preferred method for repairing composite structures, limited mainly by the amount of material removal associated with scarfing. In addition to the high strength restoration, scarf repairs also enable recovery of the original external surface as required by aerodynamic and/or external mould line considerations. However, scarf repairs almost inevitably result in the removal of undamaged material to make way for the scarf insert. This can be a particularly significant issue for thick structures, because the scarf length can vary between 20 and 100 times the thicknesses of the parent structure. In this investigation, an optimisation method has been developed for determining the optimum repair shapes for a given biaxial loading condition. The optimum scarf shape is determined by numerically solving the resulting non-linear differential equation governing the scarf angle. The optimum and near-optimum shapes are presented and discussed with respect to computational modelling using the finite element method.