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The ultrastructural diversity of the Middle and Late Jurassic serpulid tubes from the Polish Basin has been investigated. The inspection of 12 taxa representing the two major serpulid clades allowed for the identification of three ultrastructure types—irregularly oriented prismatic structure (IOP), spherulitic prismatic structure (SPHP), and simple prismatic structure (SP). Six of the studied species are single-layered and six species possess two distinct layers. Ultrastructural diversity corresponds to certain serpulid clades. The members of Filograninae have single-layered tube walls composed of possibly plesiomorphic, irregularly oriented prismatic structure (IOP). Two-layered tubes occur solely within the clade Serpulinae, where the external, denser layer is built of either the ordered spherulitic (SPHP) or simple prismatic microstructure (SP), and the internal layer is composed of irregularly oriented prismatic structure (IOP). Apart from phylogenetic signals provided by the tube ultrastructure, it can be used in analyzing paleoecological aspects of tube-dwelling polychaetes. Compared to the more primitive, irregularly oriented microstructures of Filograninae, the regularly oriented microstructures of Serpulinae need a higher level of biological control over biomineralization. The advent of the dense outer protective layer (DOL) in serpulids, as well as the general increase in ultrastructure diversity, was likely a result of the evolutionary importance of the tubes for serpulids. Such diversity of the tube ultrastructural fabrics allowed for maximizing functionality by utilizing a variety of morphogenetic programs. The biomineralization system of serpulids remains more complex compared to other tube-dwelling polychaetes. Physiologically more expensive tube formation allows for mechanical strengthening of the tube by building robust, strongly ornamented tubes and firm attachment to the substrate. Contrary to sabellids, which perform a fugitive strategy, an increased tube durability allows serpulids a competitive advantage over other encrusters. [ABSTRACT FROM AUTHOR]

Microconchid and anticalyptraeid tubeworms from the Middle Devonian of Morocco are described for the first time. The assemblage, coming from the locality of Madène el Mrakib (Mader Basin, eastern Anti-Atlas), consists of one microconchid species, Palaeoconchus sanctacrucensis, and one new anticalyptraeid species, Anticalyptraea madenensis. Both species encrusted uppermost Eifelian/lowermost Givetian brachiopod shells. P. sanctacrucensis was hitherto only known from the upper Emsian–upper Eifelian of the Holy Cross Mountains, Poland. Thus, its presence in the shelf habitats of northern Gondwana implies its migration from the southern margin of Laurussia during the transgression associated with the late Eifelian Kačák Episode. The encrustation patterns of the brachiopod shells by the Moroccan microconchids indicate that the brachiopods only served as favourable hard substrate for colonisation by the microconchid larvae. However, the occupation of different valves of the same brachiopod by microconchids and Anticalyptraea may imply that both encrusters potentially avoided direct competition for suspended food particles. Characteristics and position of Oichnus borings present on a few microconchids and anticalyptraeids indicate that they were not necessarily formed syn vivo and produced by predatory organisms. It is likely that they were drilled by some tiny suspension-feeders and may represent non-predatory domichnia. [ABSTRACT FROM AUTHOR]

Marine benthic ecosystems collapsed during the catastrophic end-Permian mass extinction, and subsequently endured a protracted phase of biotic recovery under harsh environmental conditions. In particular, metazoan reef communities almost totally disappeared and were replaced by microbe-dominated mounds during the latest Permian–earliest Triassic. Here we report the stratigraphically oldest exclusively metazoan bioconstructions from earliest Triassic (mid-Induan) strata in East Greenland — these formed within the first ca 300 ka after the Permian-Triassic boundary. Unlike the multitaxic sponge-microbe and bivalve-based buildups recorded from the Early Triassic peri-paleoequatorial Panthalassan and Tethyan margins, the East Greenland bioaccumulations developed within a restricted Boreal mid-paleolatitude seaway, and comprised a monospecific primary framework of microconchid ‘lophophorate’ tubes with shell fragments and phosphatic debris cemented by biogenic calcite. Prostrate growth of the microconchids likely facilitated their accretion into successive sheet-like biostromes and small bioherms. These are associated with a regional paleoenvironmental shift towards well‑oxygenated bottom waters, and locally punctuated sedimentation that created a favorable habitat. Although microconchids were both abundant and geographically widespread throughout the earliest Triassic, such buildups formed solely by these metazoans have not been reported from that time frame outside the Boreal Realm. These apparently flourished in the absence of more stable complex communities, and suggest that a locally variable, rather than ubiquitously sequential revival of metazoan bioconstruction activity took place in the immediate aftermath of the end-Permian extinction. However, these may also suggest that ecological recovery of benthic marine ecosystems following the end-Permian mass extinction might have started earlier in higher paleolatitudes. [ABSTRACT FROM AUTHOR]

Agglutinated worm tubes from the Upper Devonian of the Devils Gate section in Nevada, USA are reported for the first time, filling a major gap in their Palaeozoic fossil record. Two small (5 mm and 6.7 mm in length) tubes are composed entirely of tentaculitid shells, and one large tube (55 mm in length) is formed from particles including ostracode carapaces, echinoderm ossicles, tentaculitid shells and putative bryozoan fragments aligned perpendicularly to the tube's long axis. The tubes, in particular the large one have a cylindrical, curved and tapering tube morphology that is very similar to that of modern agglutinating polychaetes of the families Terebellidae and Pectinariidae. The large tube is dominated by objects that fall within a certain size-range, and although built from different types of particles, echinoderm ossicles are prevalent in the posterior part, whereas ostracode carapaces dominate in the middle and anterior parts of the tube. Tentaculitid shells are relatively rare in the large tube, despite being abundant in the surrounding host deposit. The faunal assemblage composing the tube suggests that the worm animal was rather specific in its selection of particles with a certain morphology. This is common behaviour amongst many modern agglutinating terebellid and pectinariid polychaetes. The preservation of such fragile tubes was enhanced by rapid burial, likely caused by gravity flow of sediment in a deep-slope setting. [ABSTRACT FROM AUTHOR]

The upper Frasnian coral biostrome, well-exposed in the Russkiy Brod quarry, Central Devonian Field, Russia, has been studied in detail with respect to paleoecology and sedimentary environment. The biostrome, formed by auloporid tabulates and solitary and colonial rugose corals, originated in an offshore environment characterized by calmer periods with slow or halted sedimentation, and more energetic periods when sedimentation rate increased. The episodic, higher sediment influx and stronger hydrodynamic regime are not only well-expressed in the microfacies, but also in the variability of colony integration of the rugose corals observed even within single coralla. Distinct development of constrictions, rejuvenescences and deflection of growth directions in rugose corallites may also indicate unstable sedimentary conditions. The latter features, however, may have, in part, also resulted from syn vivo biotic interaction with the associated auloporids. Both the facies and paleontological observations suggest that the biostrome originated by the colonization of deposited bioclasts by pioneering auloporids, creating the framework for settlement of later generations of auloporids and rugose corals. Apart from abundant auloporids representing a single species and associated rugose corals, the other encrusters are not numerous and poorly diversified, represented by dominating foraminifers, followed by single species of productid brachiopods, stromatoporoids, microconchids and cornulitids. The coral-associated macrobenthos has similarly a low diversity, being represented by single species of spiriferid and rhynchonellid brachiopods, and gastropods. Being developed in an offshore carbonate sedimentary system devoid of any organic-rich deposits, and characterized by extremely low abundance and diversity of suspension-feeding organisms, the biostrome is considered to have originated in a low productivity, oligotrophic environment strictly dominated by heterozoan coral communities. Its development in a well-oxygenated, oligotrophic environment during the time when organic-rich, black Kellwasser facies developed elsewhere, additionally attests for multi-causal scenarios for the Frasnian–Famennian event, during which other factors were responsible in different paleogeographic and facies settings. [ABSTRACT FROM AUTHOR]

Abstract: Carbonate cobbles from the lower Famennian (crepida conodont Zone) brachiopod shell beds of the Russkiy Brod Quarry (Central Devonian Field, Russia) have been investigated with respect to paleoecology and paleoenvironment. The cobbles, composed of similar shell bioclasts as the host deposits, were eroded from lithified shell beds during intervals of non-deposition. The smooth surfaces and the presence of borings and encrustations on all sides suggest that the cobbles were periodically transported and overturned. The fact that all the bioerosion traces are encrusted and none of the encrusters were bioeroded indicates that the first colonizers of the cobbles were worm-like suspension feeders, leaving long, cylindrical borings (Trypanites). The encrusting organisms are dominated by spirally-coiled microconchid tubeworms, followed by cornulitids, productid brachiopods, hederelloids, foraminifera, enigmatic Ascodictyon and trepostome bryozoans. The high abundance but low-diversity brachiopod fauna and general rarity of such stenohaline taxa as echinoderms in the shell beds or bryozoans on the cobbles suggest that the salinity fluctuated. The presence of dolomite crystals in both the host deposit and cobbles suggests that salinity increased from normal-marine to a higher salinity level during colonization of the cobbles. In fact, as shown by the facies and palynofacies data, the cobble-bearing deposits represent near-shore, restricted environments created during the first phases of transgression of the early Famennian that followed the regional regression at the Frasnian–Famennian transition. In such shallow, restricted settings a higher salinity could have appeared seasonally during a hot and dry climate. As with the microconchids from the aftermath of the end-Permian mass extinction, those from the post-crisis early Famennian interval of Russia were also dominant due to unstable environmental conditions. Here, at least in the case of the Russkiy Brod, the periodic higher salinity episodes may have discouraged other encrusters and thus promoted the settlement of the opportunistic microconchids. [Copyright &y& Elsevier]

A study of patterns of episkeletobiont encrustation on the shells of two early Famennian brachiopods,CyrtospiriferzadonicusandRipidiorhynchus huotinusfrom Russia, revealed assemblages comprising seven skeletonised encruster taxa. The assemblages are dominated by spirorbiform microconchids, followed by cornulitids. Features such as shell malformations, frequent encruster growth towards the commissure of the shells, and encruster distribution in the areas adjacent to zones of possible water intake by the brachiopods indicate that these may have been colonisedsyn vivo. The lack of differences in encruster abundance between the two valves inC. zadonicusindicates that this species may have lived with both valves inclined at a high angle to the substrate. The significantly higher abundance of episkeletobionts on the brachial valves ofR.huotinusmay indicate that shells of this species were oriented with the brachial valve at a lower angle to the substrate, providing sheltered sites for coelobiotic larvae. Compared with pre-Famennian brachiopod-hosted encruster communities, this early Famennian community is impoverished in species richness and is dominated by microconchids. It is proposed that the epibionts witnessed a regression-related Frasnian–Famennian extinction event. During the recovery interval, opportunistic microconchids may have been among the first encrusters to colonise the pioneering brachiopods. [ABSTRACT FROM AUTHOR]

Abstract: A diverse sclerozoan assemblages consisting of both encrusting and boring biota are described from the large limid bivalves Ctenostreon from the Callovian hardground setting of Zalas in southern Poland. At least 27 encrusting and seven bioerosion taxa are reported here, which makes this assemblage not only one of the most diverse in the Middle Jurassic, but the richest in encrusting taxa from the Callovian. The encrusters consist of cryptic biota of which sedentary polychaetes and cyclostome bryozoans dominate with respect to both species number and abundance. The bioerosion traces are dominated by tiny pits referred to the ichnogenus Oichnus, probably made by some soft-bodied biota in the present case, followed by the borings of acrothoracican barnacles (Rogerella). The first colonizers of the bivalve shells probably were borers as they only occur in the host shells. The encrusting pioneers presumably were oysters and oyster-like bivalves, followed by opportunistic serpulid/sabellid polychaetes and cyclostome bryozoans. The last colonizers were calcisponges and thecideide brachiopods. In comparison to the only known Late Callovian shallow and reef-associated, tropical sclerozoans of Israel, the assemblage from the open-marine, deeper setting of Poland is much richer in encrusting taxa. Such a surprising high encruster diversity in the marine northern paleo-latitude may have resulted from the deeper and calmer environment with a both reduced sedimentation rate and algal cover, and without any significant salinity changes, the factors that are thought to have impacted the tropical and shallow-marine sclerozoans from Israel. [Copyright &y& Elsevier]

Gierlowski-Kordesch and Cassle (2015, Earth-Science Reviews 148, 209–227) interpreted microconchids (extinct tentaculitoid encrusters) as strictly marine, rejecting the previous conclusions that these organisms occupied a variety of habitats ranging from marine to non-marine. We argue that due to misunderstanding of previous statements concerning the affinity of microconchids, the authors used an actualistic approach and incorrectly compared microconchids with modern phoronids, which led to oversimplifications and misinterpretations. Also their idea that microconchids, as supposedly strictly marine organisms, were preserved in non-marine settings only because of transport by storm surges and tsunamis is unsupported on paleontological grounds. These errors led to mistaken conclusions about microconchid paleoecology that must be discussed in order to avoid an erroneous interpretation of microconchid paleoenvironments. [ABSTRACT FROM AUTHOR]

Incised valley-fill deposits of the Middle Devonian Maywood Formation at Cottonwood Canyon, Wyoming, USA, contains a significant palynological record. Twenty-six palynotaxa were recovered, of which 21 species have wide paleogeographical distribution. The presence of the microspores Samarisporites triangulatus and Contagisporites optivus , as well as other Givetian index taxa, points to a late Givetian age (C. optivus / S. triangulatus palynozone) of the Maywood Formation. The palynoflora investigated may be correlative with the hermanni conodont Zone or a younger zone, and thus they record the latest Taghanic crisis or the earliest post-Taghanic interval. The playnoflora includes progymnosperms that had a tree-like habit (Aneurophytales and Archaeopteridales) characteristic of proximal fluvio-lacustrine settings of floodplains and paralic environments of internal basins. Spores of the herbaceous lycopsid Selaginellales, shrubby lycopods Protolepidodendrales, and primitive ferns, indicate a proximity of terrestrial plant habitats near the Maywood paleovalley. Additionally, the palynofacies (1) have amorphous organic matter and few algal remains of marine origin (Quadrisporites , Dictyotidium), (2) exist in association with assemblages of monospecific microconchid tubeworms that may have colonized non-biomineralized algae, and (3) are in strata that lack other benthic fossils, all of which indicate that the Maywood paleovalley record fluctuations of salinity. These were generated by mixing of marine and freshwater inputs within the estuarine channel, which was developed along the paleoshorelines of the Maywood Sea. • Maywood Formation assigned to Late Givetian C. optivus / S. triangulatus palynozone. • A correlation with the hermanni conodont Zone and Taghanic crisis is most probable. • Palynofacies, plant remains, microconchids record short transport to depocenter. • Arboreal progymnosperms and shrubby/herbaceous flora developed close to Maywood Sea. [ABSTRACT FROM AUTHOR]