Internal Moulds Research Articles

Devonian Pearls and Ammonoid-Endoparasite Co-Evolution

Raised shell projections on the inner shell walls that form pits on the internal moulds of Devonian ammonoids have been known for several decades. New specimens from Morocco reveal novel details of these structures; most, if not all, of which consist of a capsule of ammonoid shell that covers tiny tubes attached to the outer (= lateral or ventral) shell wall from the inside. In accordance with comparable Recent occurrences of similar structures in molluscs, we use the term “pearls” for these structures and the pits they form on the internal moulds. The nature of these encapsulated tubes is described and discussed. Because of the presence of these tubes inside the pearls, pearl arrangement, and their similarity to Recent mollusc occurrences, the tubes are interpreted as traces of parasitoses. The pearls and pits were grouped into five types based on differences in morphology, size, and arrangement. Then, having used these traits to perform a simple cladistic analysis, the resulting cladogram was compared t...

Sclerobionts on upper Famennian cephalopods from the Holy Cross Mountains, Poland

Encrustation by diverse sclerobionts is found on about 4% of upper Famennian cephalopods from the active Kowala Quarry, Holy Cross Mountains, central Poland. These infested cephalopods are represented mostly by clymeniid ammonites, but also include goniatitids and nautiloids. Sclerobionts on cephalopod shells include crinoids (represented by their holdfasts, about 57% of encrusters), moulds of problematic worm tubes (less common, about 28.5%), bryozoans, microconchids, possible cornulitids and organisms of uncertain affinities. All of the sclerobionts likely utilised shells of dead cephalopods as a hard substrate for their settlement. However, most of the infestation appears on internal moulds because the cephalopod aragonite was dissolved during diagenesis. It is possible that some of the sclerobionts encrusted exhumed lithified internal moulds. These isolated cephalopod shells and internal moulds likely served as benthic islands for various encrusters on a Devonian muddy sea-floor.

A new permian bivalve (megadesmidae, plesiocyprinellinae) from the serrinha member, Rio do Rasto Formation, Paraná Basin, Brazil

During a recent inspection in the Paleontological Collection of the Institute of Geosciences, University of Sao Paulo, we have identified some specimens of undescribed mollusk bivalves. These called our attention for the following reasons: a) all specimens are internal molds of conjugated and closed articulated valves, some of them presenting fragments of silicified shells; b) all internal molds have similar general shape and internal characters, representing specimens of the same taxon; c) the internal molds and silicified valves are well preserved, including fragile structures, which are hardly preserved, such as the internal mold of the external ligament and muscle scars; d) and equally important, according to the labels of all specimens, they were collected from rocks of the Passa Dois Group (Permian), Serrinha Member of the Rio do Rasto Formation. Although who collected the shells and the precise geographic location of the specimens are still unknown, the detailed study of these fossils brings us to the conclusion that they are morphologically distinct from any heretofore published genus of the endemic fauna of bivalves from Passa Dois Group. Based in its general shape, hinge structure and muscles scars, the new form can be classified under the Family Megadesmidae Vokes, 1967, the most diverse group of Permian bivalves of the Parana Basin. The specimens are referred as Beurlenella elongatella new gen. and sp. The shell shape and taphonomy indicate that this bivalve was a shallow, rapid, active burrower, suspension feeder, probably preserved in situ, in event deposits.

Othonella araguaiana (Bivalvia, Megadesmidae) from the Corumbataí Formation (Midlle Permian), Eastern Margin of the Paraná Basin: systematic, evolutionary and biostratigraphic significances

In this study, the occurrence of Othonella araguaiana Mendes, a rare bivalve species is reported for the first time in the Pinzonella illusa biozone, Middle Permian Corumbatai Formation, in the State of Sao Paulo. This species was originally described in coeval rocks of the Estrada Nova Formation (= Corumbatai) from the Alto Araguaia and Alto Garcas regions, State of Mato Grosso. The specimens of O. araguaiana were found in the base of a bioclastic sandstone bed, a proximal tempestite, in the middle of the Corumbatai Formation, in the city of Rio Claro, Sao Paulo State. The silicified shells and internal molds are well preserved, showing impressions of muscle scars and other internal anatomic characters (e.g., hinge), never illustrated by previous authors. In his original description, Mendes (1963) called attention to the similarity between O. araguaiana and Terraia aequilateralis, a common veneroid of the Corumbatai Formation. Conversely, Runnegar and Newell (1971) suggested that O. araguaiana belongs to Megadesmidae, being a junior synonym of Plesiocyprinella carinata (the commonest megadesmid of the Passa Dois Group). Our study indicates that O. araguaiana is indeed a megadesmid, but is distinct from the P. carinata. The new occurrence of O. araguaiana demonstrates that a) the paleobiogeographic distribution of this species is wider than previously thought (that it was restricted to the northern part of Parana Basin, Mato Grosso State); b) the molluscan fauna of the Corumbatai Formation (P. illusa biozone) in the State of Sao Paulo is more diverse and dominated by megadesmids; and c) the composition of the molluscan fauna of the Corumbatai Formation in Alto Garcas, State of Mato Grosso, is essentially the same as that of the P. illusa biozone of the eastern margin of the Parana Basin.

Early Miocene silicified limestone from Temma, northwestern Tasmania: further evidence of substantial post-Early Miocene uplift or tilting of Tasmania

Silicified shallow-water Early Miocene (Longfordian) marine limestone occurs in altitudes to over 160m, 12km east of Temma in northwestern Tasmania, the highest elevation known to date for rocks of this age and environment of deposition. Age and environmental data are provided by Foraminifera, calcareous algae and poorly preserved macrofauna. Mode of silicification of Foraminifera varies systematically between suborders - miliolids and agglutinated species as internal moulds, nodosariids, rotaliids and cibicidids as vohune-for-volume replacements. Foraminifera are benthic only. Miliolids dominate but preservation is too poor to allow statistically valid analysis. The locality provides only the second occurrence of Tenisonina tasmaniae Quilty, and, for the first time, it occurs with Sherbornina atkinsoni Chapman.

Blending Rudists with Technology; Non-destructive Examination of the Internal and External Structures of Rudists Using High Quality Scanning and Digital Imagery

Certain formations within the Cretaceous of Texas include zones of silicified rudists. Such diagenetic alteration, combined with the timing of alteration, has preserved many structural features of the rudist suitable for computed tomography (CT scanning). The excellent density differences between those skeletal structures (silica) and the internal sediment (calcitic mud) or later crystallization (calcite), fulfill a fundamental requirement for such analysis. The Jackson School of Geosciences at The University of Texas provides access to a high resolution computed tomography scanning system. This equipment, not identical to medical scanners, provides higher resolution and sophisticated software to analyze the imagery. Several rudist specimens have been scanned, including Caprinuloidea perfecta, from the Lower Cretaceous Edwards Formation (Albian) and Bayeloidea clivi from the Albian (formerly considered Turonian) of Mexico. Other rudist specimens are preserved in a different manner. For example, structures may be replaced with single crystal calcite with external skeletal intricacies especially well preserved. Elsewhere the record is one of internal molds or casts, with a reduction of available detail. Cost, diagenesis, and size determine the mode of specimen imagery used in an NSF sponsored project to image and conserve the type and figured specimens in the collection of the Texas Natural Science Center, Non-vertebrate Paleontology. This paper describes how such imagery can be used to further many aspects of rudist research. CT scanning produces serial sections of minute thickness without destroying a valuable specimen, in contrast to preparing physical serial sections, a more traditional method of analytical study. High resolution digital imagery (35 mm) provides images of great clarity which can be analyzed further and can be used as a surrogate for physical peels of rare or fragile specimens. Both these methods of imagery can be made available on-line and can be studied by scientists throughout the world.

New data on the enigmaticOcruranus–Eohalobiagroup of Early Cambrian small skeletal fossils

Abstract: TheOcruranus–Eohalobiagroup, whose members were variously considered to be brachiopods, bivalves, chitons, tommotiids and coeloscleritophorans, are difficult to classify because of lack of morphological detail and evidence for skeletal reconstruction. New specimens from South China reveal more information aboutOcruranus–Eohalobiaand allow progress towards deciphering the skeletal reconstruction and phylogenetic affinity of this enigmatic group. Many specimens have a phosphatic inner and outer coat (mould) with empty space in between that resulted from dissolution of the original shell. Moreover, many of the internal moulds show a previously unknown type of shell microstructure that consisted of stacked layers of highly organized, acicular crystallites that radiated from the apex of the shell towards the aperture. The dissolved shell and needle‐like crystals suggest an original calcareous, probably aragonitic, shell mineralogy. A few specimens also show a polygonal texture in regions that suggests the shell had a thin, prismatic inner shell microstructure.OcruranusandEohalobiabelong to the same skeleton, and we herein synonymizeEohalobiawith the olderOcruranus. Moreover, new specimens from Meishucun reveal a third type of shell plate, similar in form and inferred placement to intermediate valves of chitons.Ocruranusis likely a mollusc, and possibly a member of the chiton stem lineage. If so, then the beginning of the known record of chitons would be extended back from late Cambrian (SaukiaZone; Furongian) to early Cambrian (Meishucunian; Series 1).

New and exceptional discovery in the Upper Cretaceous of the Iberian Peninsula: the palaeontological site of “Lo Hueco”, Cuenca, Spain

The palaeontological site of “Lo Hueco” was discovered in Cuenca, Spain, in 2007. It includes a stratigraphic interval in “Garumn” facies belonging to the upper part of the Villalba de la Sierra Formation. A succession of versicolor marly mudstone levels (V, G1, R1, G2, R2 and M) can be observed at the site studied. This succession is partially modified by a sandy channel structure (C) and by a sulphated interval (S). The C structure and the G1, G2 and R2 (lower part) levels have an extremely rich and varied fossil concentration and have provided to date more than 8500 macroremains. These are mainly from vertebrates, but also from plants and invertebrates. In general, vertebrates are represented by mineralized bones with an early infilling of gypsum, a ferruginous crust, and a secondary precipitation of gypsum; invertebrates by internal moulds; and plants by carbonized remains. Among the vertebrates, titanosaur dinosaurs (some of them with partially articulated skeletons) are by far the most common representatives, although lepisosteid fishes, bothremydid turtles, squamate lizards, eusuchian crocodiles, and ornithischian and theropod dinosaurs are also well represented. The relative stratigraphic position and the palaeontological content of this site allow to attribute it to the upper Campanian-lower Maastrichtian. Interpretation of its materials suggests a near coast muddy flood plain crossed by distributary sandy channels environment, exposed to brackish to fresh water aquatic influence.

The oldest South Australian cowries (Gastropoda: Cypraeidae) from the Paleogene of the St Vincent Basin

Yates, A.M., March, 2009. The oldest South Australian cowries (Gastropoda: Cypraeidae) from the Paleogene of the St Vincent Basin. Alcheringa 33, 23–31. ISSN 0311-5518. Two occurrences of cowries in the Paleogene of the St Vincent Basin are described. Two cypraeid internal moulds from the late Eocene (Aldingan) Blanche Point Formation comprise one such occurrence. These are among the oldest recorded Australian cypraeids. They bear some resemblance to the genera Zoila and Umbilia but insufficient details are preserved for accurate identification. The second occurrence consists of a series of internal and external moulds from the early Oligocene of the Port Willunga Formation. These represent a new species of the endemic subgenus Lyncina (Austrocypraea), here described as L. (A.) onkastoma. This species is the oldest known member of the subgenus but its apparently derived characteristics indicate that the subgenus had already diversified by this time.

A GIANT LUCINID BIVALVE FROM THE EOCENE OF JAMAICA – SYSTEMATICS, LIFE HABITS AND CHEMOSYMBIOSIS (MOLLUSCA: BIVALVIA: LUCINIDAE)

Abstract: The giant bivalve Lucina megamerisDall, 1901, from the late Eocene White Limestone Group of Jamaica and by far the largest known species of the family Lucinidae, is placed in a new genus Superlucina. Apart from its large size, with a shell height exceeding 310 mm, it is distinguished from other genera, such as Pseudomiltha and Eomiltha by external shell characters and the extremely long and narrow, anterior adductor muscle scar. Features preserved on internal moulds suggest that, in common with living Lucinidae, S. megameris was chemosymbiotic with sulphide – oxidizing bacteria housed in the gills. Palaeoenvironmental evidence suggests a habitat in oligotrophic, shallow waters, probably in seagrass beds, with an associated molluscan fauna including large cardiids that may have been photosymbiotic. Superlucina is considerably larger than any living lucinid that range in size from 3 to 150 mm with most encompassed within 5–30 mm. From the Jurassic onwards, a few other large lucinids are known from cold seep sites, with several other records from possible shallow water seagrass beds.

Campanile trevorjacksonisp. nov. (Mollusca: Gastropoda) from the Eocene of Jamaica: at last, a name for the first fossil used in intercontinental biostratigraphic correlation (de la Beche 1827)

AbstractA new species of giant fossil gastropod belonging to the genusCampanile,Campanile trevorjacksonisp. nov., is described from the Lower Eocene Stettin Formation of the Yellow Limestone Group of Jamaica. Over 180 years ago, internal moulds of these giant gastropods were first reported from the Eocene of Jamaica and referred to asCerithium; it is only with the discovery of an external mould of the shell spire that it can now be removed from open nomenclature. The ornate shell ofC. trevorjacksonihas flat‐sided to slightly rounded whorls; straight, impressed sutures; seven beaded, spiral cords per whorl and a nodose subsutural ridge in the more adapertural part of the shell. This sculpture differentiatesC. trevorjacksonifrom other PaleogeneCampanilespecies. In 1827, de la Beche includedC. trevorjacksoni(asCerithium) in a list of over 20 taxa with which he correlated his white limestone formation (including the Yellow Limestone Group of modern use) with the (Eocene)Calcaire grossierof the Paris Basin. These specimens are lost, but re‐examination of de la Beche's list suggests his identifications were mostly reasonable. Copyright © 2008 John Wiley & Sons, Ltd.

Distinction between fill channels and abrasion furrows on ammonoid internal moulds

Ammonoid sedimentary internal moulds can display grooves on the external or ventral region that have been formed by diverse taphonomic processes. In particular, draft-filling spiral channels and abrasion annular furrows are taphonomic structures useful as palaeoenvironmental indicators of turbulent waters and conditions of low rate of sedimentation, although they can show some common morphological properties that may lead to erroneous identifications. However, the morphological features, formation processes and palaeogeographic conditions in which the structures of these two types have been developed are very different. In consequence, it is important to keep in mind the distinctive characters of these taphonomic structures before using their occurrence in the palaeoenvironmental or palaeogeographic interpretations.

Late Triassic megalodontids (Bivalvia) from the headwaters of the Yangtze River, Qinghai province, west China

A bivalve faunule of six species is described from the Upper Triassic Jiapila Formation at the headwaters of the Yangtze River, southern Qinghai, China. The new species, Neomegalodon cornutus and Quemocuomegalodon circularis, are described. The type species of Quemocuomegalodon, Q. orientus, is revised. Quemocuomegalodon orientus Yao, Sha, and Zhang (2003) is now known from abundant, well-preserved specimens that show great variation in shape, size, thickness of shell, and dentition, and the species Q. longitatus, Yao, Sha, and Zhang (2003) is now placed in synonymy with Q. orientus. There are significant morphologic differences between the external appearance of shelled specimens and the internal molds of species of Quemocuomegalodon. This suggests the need for the re-evaluation of many megalodontid species from elsewhere that are known only from internal molds.

Ammonoid taphonomy, palaeoenvironments and sequence stratigraphy at the Bajocian/Bathonian boundary on the Bas Auran area (Subalpine Basin, south‐eastern France)

Bas Auran, in south-eastern France, is the candidate area for Global Boundary Stratotype Section and Point (GSSP) of the base of the Bathonian Stage (Middle Jurassic). In the Bas Auran area, upper Bajocian and lower Bathonian deposits are made up of limestone beds alternating with marls that correspond to the ‘Marno-calcaires a Cancellophycus’, below the ‘Terres Noires’ Formation. Taphonomic analyses of the successive ammonoid fossil assemblages provide new and complementary data for biostratigraphic completeness, palaeoenvironmental setting and sequence stratigraphy. Lithologic differentiation between limestone and marl intervals resulted from alternating episodes of carbonate input and starvation. Both lithologic phases may contain evidence for sedimentary and taphonomic reworking, associated with scours, that reflects low rates of sedimentation and stratigraphic condensation. Three successive types of elementary cycles resulted from increasing rates of stratigraphic condensation, sedimentary condensation and substrate stabilization during early Bathonian. The occurrence of reelaborated ammonoids (i.e. exhumed and displaced before their final burial) implies that tractive current flows or winnowing affected the burial of concretionary internal moulds. In the lower Bathonian strata, the dominance of homogeneous concretionary internal moulds of phragmocones, completely filled with sediment, is indicative of low rates of sedimentation and sediment accumulation, respectively associated with low degrees of stratigraphic and sedimentary condensation. However, at the Bajocian/ Bathonian transition, hemipelagic, bed-scale limestone–marl alternations show a maximum value of biostratigraphic completeness and there is no evidence for taphonomic condensation in the ammonoid fossil assemblages. Taphonomic analyses of the successive ammonoid fossil assemblages and taphofacies confirm the development of a deepening phase associated with sedimentary starvation, which characterizes the last episode within the deepening half-cycle of third and second order cycles, in the Bas Auran area of French Subalpine Basin during early Bathonian.

‘Screwstones’ from the Lower Carboniferous (Mississippian; Visean, Brigantian) at Bradford Dale, Youlgrave, Derbyshire, and a new species of Gilbertsocrinus Phillips (Echinodermata, Crinoidea)

SUMMARY Screwstones are chert clasts from the Lower Carboniferous (Mississippian) of Derbyshire in which the internal moulds of the axial canal of crinoid pluricolumnals have a screw-like appearance. They are commonly regarded as curiosities, but chert can preserve the morphological details of crinoid ossicles exquisitely. The thecae of Gilbertsocrinus occur only in the Tournaisian (Ivorian to Chadian) of the British Isles, yet their distinctive columnals range from Upper Devonian (Famennian) to Visean (Brigantian) in the same region. The youngest such columnals, rounded in outline with a narrow to moderately broad marginal crenularium, a broad pentalobate lumen, and heteromorphic with two orders of internodal, are described as Gilbertsocrinus fionae sp. nov. from cherts of the Monsal Dale Limestone Formation of Youlgrave, Derbyshire.

TAPHONOMY OF A MIDDLE PENNSYLVANIAN MARINE VERTEBRATE ASSEMBLAGE AND AN ACTUALISTIC MODEL FOR MARINE ABRASION OF TEETH

Abstract The taphonomy of assemblages of disarticulated remains of marine vertebrates is not well studied. Examination of a Middle Pennsylvanian chondrichthyan assemblage from Kohl's Ranch, Naco Formation, central Arizona, contributes to knowledge of such assemblages and reveals a complex taphonomic history. This vertebrate assemblage is restricted to two thin horizons associated with a concentration of disarticulated and tightly packed invertebrates. The vertebrate specimens are associated with phosphatic internal molds of molluscs and bryozoans. Most vertebrate specimens show abrasion. Several lines of evidence suggest that the specimens were abraded in a nearshore wave environment and subsequently transported offshore by a storm surge, where they were incorporated into an environmentally condensed assemblage. In particular, the presence of abrasion, a concentrated skeletal assemblage, significant amounts of siliciclastic sand, presence of intraclasts, phosphatic molds, and a basal lithologic discontinu...

Shell microstructure and morphogenesis of the ornamentation in Cymatoceras Hyatt, 1883, Cretaceous Nautilida. Systematic implications

The transverse ridges or so-called ‘ribs’ of Cretaceous Cymatoceras correspond to the juxtaposition of thick, projected and imbricated radial tile-shaped lamellae of outer prismatic layer. Each of these lamellae formed in a cycle including an outward extension and secreting phase of the mantle edge, followed by his temporary withdrawal behind the periphery of the lamella. The sculpture of the underlying nacreous layer reflects only the underlying morphology of the juxtaposed adapical parts of the imbricated lamellae of outer prismatic layer. On internal moulds, the subdued symmetric undulations, which reflect the internal surface of the nacreous layer, can easily be mistaken for imprints of comarginal ribs (this last term is restricted here to undulations of the outer shell without structural discontinuities other than growth lines). Distinction of this kind of ornamentation challenges the monophyly of the family Cymatoceratidae, classically interpreted to include all ‘ribbed’ post-Triassic Nautilida, the so-called ‘ribbing pattern’ encompassing lamellae, fasciculate growth lines and divaricate ornamentation. Whether or not radial tile-shaped lamellae of outer prismatic layers a synapomorphy of an emended ‘cymatoceratid’ clade cannot be solved until its history can be traced through a well-corroborated phylogeny, allowing in turn the evaluation of the hypothesized heterochronic (paedomorphic) shifting of the embryonic growth pattern trough post-embryonic development.

Eoshumardia (Trilobita, Cambrian), a junior synonym of Koldinioidia

Well-preserved internal and external moulds of a shumardiid species are described from the late Furongian (Late Cambrian) “Fengshan Formation” at Poben, Napo, southwestern Guangxi, which is close to the type locality of Shumardia orientalis, the type species of Eoshumardia. All features observed on the internal moulds indicate that the new material is definitely S. orientalis, whereas the morphology of the external moulds indicates that S. orientalis should be referred to Koldinioidia. The change of generic assignment of the type species means that Eoshumardia is a junior synonym of Koldinioidia.

Geochemistry and mineralogy of the Paleocene/Eocene boundary at Gabal Dababiya (GSSP) and Gabal Owaina sections, Nile Valley, Egypt

This work deals with the geochemical and mineralogical characteristics of the period representing the Paleocene-Eocene Thermal Maximum (PETM) succession, at both the Gabal Dababiya Paleocene-Eocene GSSP and the Gabal Owaina sections. At both sections, the sediments deposited during this interval contain varied amounts of phosphatized and silicified fish debris, pyrite framboids, pseudomorphs of hematite spherules, calcite and detrital minerals. At Gabal Dababiya, the PETM succession is characterized by strong anomalies inmost chalcophiles, especially in the lower part of the clay bed, aswell as in the coprolite-rich and the bone-bearing strata. In contrast, such concentrations of the chalcophile elements have not been recorded at G. Owaina. This leads to the conclusion that these trace elements are incorporated in the phosphatic components (fish debris and coprolites) and in the clay-fraction and/or organic matter. The association of SiO2*-excess, and P2O5 enrichment with an abundant radiolarian fauna and enrichment of the organic matter within the first three beds of Dababiya Quarry Beds, indicates high productivity and upwelling throughout their deposition. In the course of the upwelling activity,water rich in nutrients rose to the surface, enriching sediments with organic matter. The increased consumption of oxygen caused by the sinking of organic carbon to the bottom resulted in a redox front at or just above the sediment-water interface. At G. Owaina, the internal molds of radiolarians, as well as benthic and planktonic foraminifera which are represented by hematite spherules, are abundant in the post-PETM succession. This is an indication that silica and calcite dissolution, rather than low productivity accounts for the absence of opaline silica and biogenic calcite. Solutions resulting from the dissolution of siliceous and calcareous oozes may have penetrated lower layers and formed Ca-Si-rich components (silicified fish debris and Ca-Si-rich phase).

Evidence for ammonite survival into the Danian (Paleogene) from the Cerithium Limestone at Stevns Klint, Denmark

Two ammonite species, Baculites vertebralis and Hoploscaphites constrictus, are recorded from the Cerithium Limestone (lower Danian, Paleogene) at Stevns Klint, Denmark. Most of the specimens represent internal and external moulds of shell fragments, the sole exception being a complete, well preserved internal mould of H. constrictus. The infilling of the body chamber and phragmocone of this specimen is indistinguishable from the surrounding limestone. The ð13C value for the phragmocone fill is 1.382, matching Danian values much better than the more positive Maastrichtian values for the fine-fraction ð13C curve of the Stevns Klint succession. Additionally, the phragmocone infill contains Operculodinella operculata, a calcareous dinocyst typical of the Danian at high latitudes. The specimen is thus interpreted to be an indigenous early Danian ammonite. In view of the mass occurrence of calcitic bryozoans, brachiopods, and bivalves in the topmost Maastrichtian chalk at Stevns Klint, the total absence of brachiopods and near-absence of bryozoans and calcitic bivalves in the Cerithium Limestone provide evidence against significant redeposition of Maastrichtian fossils into the latter unit. Consequently, all ammonites from the Cerithium Limestone studied are interpreted as early Danian survivors.