Living on an island: characterization of the encrusting fauna of large pectinid bivalves from the Lower Cretaceous of the Neuquén Basin,west‐central Argentina

Exposed mollusc shells may act as benthic islands in soft bottoms, and the analysis of their encrusting faunas provides unique palaeoecological information. In the late Valanginian of the Agrio Formation (Neuquén Basin, west‐central Argentina), the large pectinid Prohinnites acted as a benthic island on soft substrates. Inequivalved Prohinnites adults with small, smooth cementing scars on the right valve suggest that a free reclining life habit followed the epibyssate juvenile and cementing phases. The encrusting fauna on Prohinnites was studied taxonomically and palaeoecologically by means of a quantitative approach. Over 90% of 123 valves presented encrusters. Encrustation was equally common in both valves. Internal encrustation was rare. The left umbonal region was less encrusted probably due to sediment accumulation or early colonization by soft‐bodied taxa. The fauna was composed of 14 encrusting taxa, including oysters, serpulids, sabellids and cyclostome bryozoans. Oysters exceeded 50% of the total abundance, but serpulids and bryozoans were more diverse. Serpulids and particularly oysters showed a gregarious life habit. Few interactions took place among encrusters and most were post‐mortem, involving the overgrowth of already dead oysters. The oysters were early settlers that took advantage of their gregarious behaviour to rapidly cover available hard surfaces. However, they were unable to exclude bryozoans and polychaetes, which settled on the pectinid's valves regardless of the presence of oysters. The studied fauna corresponds to a climax community that was structured by larval abundance rather than by competitive interactions; oysters settled first and replenished themselves while polychaetes and bryozoans settled over or alongside them     

Origin and paleoecology of Middle Jurassic hiatus concretions from Poland

Bored and encrusted carbonate concretions, termed hiatus concretions, coming from the Middle Jurassic (Upper Bajocian and Bathonian) siliciclastics of the Polish Jura, south-central Poland, have been subjected to detailed paleoecological investigation for the first time. The concretions possess variable morphology and bear distinct traces of bioerosion and encrustation as a result of exhumation on the sea floor during intervals of low sedimentation and/or erosion. The borings are dominated by Gastrochaenolites and Entobia. Epilithozoans, represented by at least 26 taxa, are dominated by sabellid/serpulid worm tubes and bryozoans, while sponges and corals are minor. No relationship between the concretion size and the number of encrusters has been found, suggesting that concretion size was not the primary factor controlling diversity. Stable isotope analyses and the presence of crustacean scratch marks and Rhizocorallium traces on many of the hiatus concretions indicate that they formed just below the sediment–water interface, within the sulfate reduction zone. Moreover, crustacean activities may have been a prelude to their origin, as shapes of many concretions closely resemble thalassinoidean burrow systems. It is also possible that crustacean activity around the concretions promoted their exhumation by loosening the surrounding soft sediment. The presence of borings and encrusters on different concretion surfaces, as well as truncated borings and a number of abraded epilithozoans, indicate that after the concretions were exhumed they were repeatedly overturned and moved on the sea floor, probably due to episodic storm-related bottom currents in shallow subtidal environment.     

Determination of a Late Miocene rocky palaeoshore by bioerosion trace fossils from the Bozcaada Island, Çanakkale,Turkey

Bioerosion is a common process in hard substrates. This study introduces an example from the rocky palaeoshore cropping out at a sea cliff on the Bozcaada Island. It includes bioerosion trace fossils preserved in limestone boulders of the shallow marine and lacustrine Alcitepe Formation of Late Miocene age. The ichnotaxa include borings produced by duraphagous drillers (Oichnus isp.), phonorids (cf. Conchotrema isp.), clionid sponges (Entobia cf. goniodes, Entobia geometrica, Entobia laquea, Entobia ovula, E. cf. solaris, Entobia isp.), endolithic bivalves (Gastrochaenolites torpedo, Gastrochaenolites lapidicus, Gastrochaenolites isp., Phrixichnus isp.), polychaete annelids (Maeandropolydora isp., Maeandropolydora sulcans, Maeandropolydora decipiens, Caulostrepsis taeniola, Caulostrepsis isp.), echinoids (cf. Circolites isp.) and spinculid worms (cf. Trypanites isp.). Barnacles are also common as encrusters. The borings can be ascribed to the Gastrochaenolites-Entobia assemblage, which is typical of Neogene rocky-shores. They belong to the Entobia ichnofacies indicating various conditions of light, energy, and depth. Therefore they can reveal environmental changes and play an important role in forming palaeo-rocky shores and wave-cut platforms during marine trangressive events.     

Paleoecology of epizoans and borings on some Upper Cretaceous chalk oysters from the Gulf Coast

Analysis was made of a hard substrate fauna found on right valve interiors and exteriors of the epifaunal reclining oyster Pycnodonte mutabilis from the Maastrichtian (Navarroan) Saratoga Formation (southwestern Arkansas). Comparison of boring and encrustation patterns on both sides of valves indicates that a major portion of colonization on valve exteriors occurred while host oysters were alive. Paleoautecologic information derived from such valve exterior patterns includes evidence of rheotropic orientation by encrusting juvenile P. mutabilis and preferential location of Trypanites sp. borings in surficial shell grooves. Valve exteriors supported a hard substrate paleocommunity which had the following non-interactive progressive colonization sequence: (1) Trypanites sp. and P. mutabilis juveniles; (2) Entobia sp., serpulid worm tubes, and Bullopora sp.; and (3) cheilostome bryozoans. This sequence could have been caused by low seasonality and ranked success of colonizing encrusters and borers. Colonization of valve interiors generally differed from exteriors only in that many interiors were first colonized by the clionid sponge that created Entobia sp., which had already occupied the exterior, and which quickly bored through the valve to occupy the interior upon the host's death. □ Trace fossils, epizoans, borings, Gryphaeidae, palaeoecology, communities, colonization sequence, Late Cretaceous, Maastrichtian, Navarroan, Arkansas.     

Ultrastructure and mineral composition of serpulid tubes (Polychaeta,Annelida)

We have studied the tube ultrastructure of 44 recent species from 36 serpulid genera. Twelve distinct ultrastructures are identified. Serpulids possess very diverse tube ultrastructures, in contrast with the traditional point of view. Most species show single‐layered tubes, but 34% of these species have between two and four ultrastructurally different layers. Tubes are mostly bimineralic, and are composed of aragonite and calcite; however, one of the polymorphs is always dominant. All the studied single‐layered tubes with a lamello fibrillar tube ultrastructure are exclusively calcitic; prismatic structures, both in regular or irregular orientation, are either calcitic or aragonitic in composition. There is no correlation between tube mineralogy, and ultrastructure, and marine, brackish, and freshwater environments. We find that 47% of the serpulid species studied possess a unique combination of tube structure characters. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 633–650.     

Contribution to the revision of some late Callovian serpulids (Annelida, Polychaeta) of Central Russia: Part 2

This paper deals with the revision of the species of the genera Mucroserpula, Propomatoceros, and Spiraserpula (family Serpulidae) from the Upper Callovian of the locality Peski (Moscow Region). All taxa are described in accordance with the current classification of fossil serpulid tubes. Two new species are described: Propomatoceros barskovi sp. nov. and Spiraserpula oligospiralis sp. nov.     

Microconchid encrusters colonizing land plants: the earliest North American record from the Early Devonian of Wyoming,USA

Caruso, JA. & Tomescu, AM.F. 2012: Microconchid encrusters colonizing land plants: the earliest North American record from the Early Devonian of Wyoming, USA. Lethaia, Vol. 45, pp. 490–494. Plant fossils in the Early Devonian Beartooth Butte Formation (Wyoming, USA) are colonized by microconchid encrusters which are found on several plant taxa, at two fossil localities in the formation, and whose tube coil diameters range from 230 to 1170 μm. Colonization is densest on broad Drepanophycus devonicus stems where microconchid individuals encompassing broad size ranges co‐occur in close vicinity. This indicates exposure to microconchid colonization and, therefore, submergence of the plant material for relatively extended periods of time prior to burial. For in situ preserved Drepanophycus, this suggests that the plants grew partially submerged and their submerged parts were colonized by microconchids while still alive. In turn, this indicates that by the Early Devonian microconchids were colonizing freshwater environments. The Beartooth Butte Formation provides the first record of plant colonization by microconchids in North America and, along with only one other Early Devonian record from Germany, the oldest evidence for microconchids colonizing plant substrates. □Devonian, encrusters, microconchid, vascular plants, Wyoming.     

Les sclérobiontes des huîtres du Cénomanien supérieur du Mans (Sarthe,France)

Oysters of the Marnes à Pycnodonte biauriculata Formation, Upper Cenomanian (Guerangeri biozone) were significantly sampled in building works within the town of Le Mans (Sarthe, France). They are colonized by episkeletobionts (encrusting organisms) and endoskeletobionts (boring and bioeroding organisms). First ones include bivalves, polychaetes, foraminiferans and bryozoans. Second ones are represented by about fifteen ichnotaxa, the producers of which, when they are known, belong to ten taxa. The oysters, some of which have a large fixation surface, are allochtonous or at least parautochtonous. The settlement of sclerobionts began when the oysters were alive (Entobia isp.) and continued post-mortem on isolated valves, transported in their final depositional environment (Gnathichnus pentax). The significance of the coexistence of both Entobia and Gnathichnus ichnocoenosis is discussed.     

The encrustation of fossil and recent sea-urchin tests: ecological and taphonomic significance

A comparison of fossil ( Echitwlampas sp. from the Lower Miocene Zogelsdorf Formation, Austria) and Recent ( Schizaster canaliferus from the northern Adriatic Sea) irregular sea-urchin tests shows that, upon their death, burrowing echinoids can serve as a substrate for a dense epigrowth. Size, shape, stable orientation, and surface residence-time were identified as key factors governing encrustation. The encrusters on fossil Echinolampas were bryozoans, serpulid polychaetes, barnacles, and coralline algae, while the recent material was initially encrusted by serpulids and hydrozoan colonies, and ultimately covered by the full range of sessile, hemi-sessile, and vagile species characterizing the benthic community in the Adriatic. In Echinolampas , epigrowth was more abundant on the lower (oral) surface; this specific distribution was echoed in S. canaliferus , where epigrowth started on the bottom side and grew upward. This indicates that the tests have a stable orientation and a surface residence-time long enough to allow intense encrustation. A taphonomic model is developed, and the role of encrustation on such special substrates for overall community structure is discussed. The Recent/fossil comparison provides new insights for both fields of study: the recent material indicates the role of soft-bodied faunas as well as the complexity of small-scaled ecological processes; the fossil material reflects many of the above phenomena and adds important taphonomic details on the fate of encrusted biogenic structures and on encruster growth patterns and distributions.     

Lapworthellids and other skeletonised microfossils from the Cambrian Stage 3 of the northern Montagne Noire,southern France

The Montagne Noire (southern France) possesses one of the most complete Cambrian successions in the western peri-Gondwana margin and might provide a good stratigraphic reference for both regional charts and international correlations. However, to date, the lower Cambrian succession of the northern Montagne Noire has been supposed to be devoid of biostratigraphically significant fossils. The complex tectonostratigraphic framework of the area (a range divided into Axial Zone, northern and southern Montagne Noire) exacerbated problems related to regional correlations and palaeogeographic reconstructions. As a result, the chronostratigraphic context of the lower Cambrian of northern Montagne Noire is still uncertain and stratigraphic reports have broadly relied on putative lithostratigraphic correlations with the southern Montagne Noire. The purpose of this study is to characterise, for the first time, the fossil record of carbonate beds and lenses of the northern Montagne Noire occurring at the top of the siliciclastic-dominated Marcory Formation, in order to provide regional bio- and chronostratigraphic constraints on lower Cambrian strata. Moreover, this study is aimed at improving international chronostratigraphic correlation. Carbonate beds and lenses cropping out along the Orque Cliff, in the Mélagues thrust slice, were investigated. They yielded a faunal assemblage constituted of molluscs (Igorella cf. ungulata and Igorella moncereti n. sp.), hyoliths (Conotheca brevica), chancelloriids (Archiasterella cf. pentactina and Allonnia sp.) and tommotiids (Lapworthella rete). L. rete is recorded in upper Meishucunian (Cambrian Stage 3) strata of the Yangtze Platform (South China) where it is used as index fossil of the Cambrian Stage 3 Sinosachites flabelliformis–Tannuolina zhangwentangi Assemblage Zone. Therefore, the presence of this tommotiid provides evidence that the studied carbonate beds and lenses are Cambrian Age 3 (Atdabanian according to the Siberian chart). The upper part of the Marcory Formation in the Mélagues slice, dated as Cambrian Stage 3, might represent a lateral equivalent of the mixed (carbonate-siliciclastic) Pardailhan Formation defined in the southern Montagne Noire.     

Middle to Late Pleistocene herpetofauna from Scladina and Sous-Saint-Paul caves (Namur,Belgium)

For the first time, the fossil herpetofauna from the Middle and Late Pleistocene of Scladina and Sous-Saint-Paul caves (Sclayn, Belgium) is described. The amphibians and squamate reptiles are represented by one salamander (Salamandra salamandra), three anurans (Pelodytes punctatus, Bufo bufo and Rana temporaria), two lizards (Lacerta cf. agilis and Anguis fragilis) and two snakes (Zamenis longissimus and Vipera cf. berus). The occurrence of the Parsley Frog (Pelodytes punctatus) and the Aesculapian Snake (Zamenis longissimus), which are not currently represented in Belgium, is of particular interest. Scladina also represents one of the northernmost fossil mentions for the Fire Salamander (Salamandra salamandra) although it is within its current distribution in Europe. Finally, the presence of the Adder (Vipera cf. berus) is very probably attested in Scladina whereas today this snake is infrequent and classified as endangered in Belgium.     

Decapod Crustacea from the Agrio Formation (Lower Cretaceous) of the Neuquén Basin,Argentina

Abstract: Two species of decapod crustacean are recorded from the Agua de la Mula Member of the Agrio Formation (Upper Hauterivian – Lower Barremian) of the Neuquén Basin of west‐central Argentina, namely Astacodes falcifer Bell and a new species of Palaeohomarus, P. pacificus. The preservation of the specimens is exceptional, some showing delicate compound eyes and a stridulatory apparatus, features rarely found in fossil forms. Many specimens are preserved articulated inside calcareous nodules, within dark‐grey shales. The lobster‐bearing sediments accumulated in a low‐energy marine environment and diagenetic mineralization occurred very rapidly, prior to significant decay, thus allowing exceptional preservation of specimens. Palaeohomarus was a rare genus in the Cretaceous with a palaeogeographic distribution restricted to the Mediterranean Tethys, the eastern USA and Madagascar, while Astacodes falcifer has been recorded only from Speeton (eastern England) and Neuquén.     

Über parasitische Polychaeten in Kreide-Austern sowie einige andere in Muschelschalen bohrende Würmer

Shells of oysters from Turonian strata in Westphalia contain dwelling tubes of polychaete worms sunk into the shell material. The roofs of the tubes consist of shell material secreted by the oysters. Thus the tubes are intra vitam deformations of the shell, resembling the “mudblisters” of recent oysters. Usually, they are directed centripetally towards the muscle scar and have a round external opening perforating the shell. They are described asOstreoblabe perforans n. g. n. sp. Since they were probably oriented with their front part toward the inside of the shell, penetrating the pallial line, they were most likely parasites. In addition, long, meandering furrows sunk into the shells of pelecypods are described asMaeandropolydora decipiens n. g. n. sp. andM. sulcans n. g. n. sp. The realPolydora is not found in Pre-Tertiary strata and is probably not related genetically toPolydora-like forms (Caulostrepsis) in Devonian strata.     

Upper Pliocene bivalve shell concentrations from the Lower Chelif basin (NW Algeria): Systematics,sedimentologic and taphonomic framework

Sedimentologic and palaeontological investigation of the Upper Pliocene Slama Formation in the Lower Chelif Basin (NW Algeria) led us to collect important bivalve assemblages for taxonomic and taphonomic purposes. A rather comprehensive inventory list of Upper Pliocene bivalves from northwestern Algeria is now available and consists of 30 species, 17 of which are extinct ones. Four principal taphonomic attributes were analysed: bioerosion, encrustation, fragmentation, and abrasion. Physical and biogenic sedimentary structures are used for palaeoenvironmental interpretations. The taphonomic, sedimentologic and ichnological characteristics of most of the deposits suggests they originated from discontinuous processes of winnowing and bypassing of sediments, probably due to the action of storms in shallow waters, mainly in the shoreface depositional environment. The bivalve assemblage is dominated by disarticulated valves and displays significant taphonomic alteration in the shells. Sclerobionts traces in shells particulary affect the oyster shells. Bioerosion traces are predominately those of clionid sponges (Entobia isp.), polychaetes (Maeandropolydora isp. and Caulostrepsis isp.), bivalves (Gastrochaenolites isp.), and of predatory gastropods (Oichnus isp.). Among the sclerobionts, the identified encrusters were juvenile oyster recruits, barnacles, polychaetes (serpulid tubeworms), bryozoans (Microporella sp. and Acanthodesia sp.), and vermetid gastropods (Petaloconchus intortus).     

Palaeoecology of coralline sponge-coral meadows from the upper jurassic of Portugal

TheComophyllia polymorpha-Crispispongia cf.expansa association of the Kimmeridgian Alcobaça Formation occurs in a 5–10 m thick unit that can be followed for at least 10 km in the vicinity of Alcobaça (Estremadura). Corals, coralline sponges (mainly Calcarea), cryptalgal crusts and, to a lesser extent, crinoids are the dominant constituents of the autochthonous community relic which can be grouped in framebuilders, framework encrusters, frame binders, reef-dwellers, and reef destroyers. These organisms formed low meadows in a shallow, fully marine environment subject to low rates of sedimentation and moderate to low energy levels punctuated by rare high energy events. The abundance of coralline sponges in reefs and reef-like communities is uncommon in the Jurassic and appears to be restricted to very shallow water environments.     

Hettangian (Early Jurassic) Dinosaur Tracksites from the Mecsek Mountains,Hungary

A rare example of a North American Jurassic hardground is found in the Carmel Formation of southwestern Utah. The Carmel hard‐ground was formed across a carbonate lagoon from an oolitic shoal seaward to a subtidal shelly facies landward. It has an abundant bivalve fauna consisting of thick layers of encrusters (the oyster Liostrea and the plicatulid Plicatula), borers (the ichnofossil Gastro‐chaenolites with the mytilid Lithophaga often preserved inside), and nestlers (the mytilid Modiolus). A rare soft‐bodied bryozoan (Arach‐nidium) is preserved by bioimmuration in the attachment scars of Liostrea; this is the first bioimmuration recorded from the Jurassic of North America, and the first bioimmuration recorded from a hard‐ground. The phoronid boring Talpina is present in some Liostrea shells; it was apparently excavated after the death of these oysters. The Carmel hardground community does not contain other fossils, such as serpulids, brachiopods, foraminiferans, and skeletal bryo‐zoans, typical of Jurassic hardgrounds elsewhere. It represents a low diversity molluscan community developed in a restricted marine environment.     

Arachnostega n. ichnog. -burrowing traces in internal moulds of boring bivalves (late jurassic,northern Germany)

Burrowing traces in internal moulds of molluscs are described asArachnostega gastrochaenae n. ichnog. n. ichnosp. Currently, the ichnogenus is only known from the Late Jurassic and Recent of Northern Germany. The synecology of its polychaete producers is discussed in detail: they were probably opportunistic detritus-feeders and have to be regarded as infaunal coelobites. The tracemakers were not part of an ecological succession because their activity was facilitated by a sedimentation event. They weakened the skeletal frame but rapid cementation and encrusters inhibited them. Finally, aspects of biostratinomy and fossil diagenesis are sketched.     

A palaeoecological study of the Upper Coralline Limestone, Terebratula-Aphelesia bed (miocene,malta) based on bryozoan growth-form studies and brachiopod distributions

A prominent bed, containing brachiopods and ectoproct bryozoans, is widely distributed within the Maltese Islands, being associated with a coralline algal rhodolite bioherm. This bed provides a useful stratigraphic marker horizon at the base of the Upper Coralline Limestone Formation.Samples taken from the bed at localities in Malta and Gozo have been examined and their contained biodata studied. Distribution analysis of the bryozoan growth-forms present has permitted recognition of four assemblages, dominated by cellariform, vinculariiform, encrusters, and cellariform and vinculariiform bryozoan growth-forms, respectively. Morphological variations and distributions of brachiopods contained within the samples were also examined and these were compared with the bryozoan growth-form distributions previously obtained. An interpretation of the palaeoecology of the four common brachiopod species, Terebratula terebratula, Aphelesia bipartita, Argyrotheca cf. cordata and Megathiris decollata, is offered partly on the basis of present-day brachiopod ecology but mainly on the basis of information gained for the bryozoans. Interpretations of the palaeoecology of several other common invertebrate genera, also based on the bryozoan growth-form distributions, are also presented.