The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14–23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan (Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three‐dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal‐dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal‐dominated reef evolution and the ensuing development of reefs during the Middle–Late Ordovician. □Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef.     

Unusual compound zooecia in the trepostome bryozoan Eostenopora from the Devonian of Guizhou,China

Enlarged, ‘compound zooecia’ are described for the first time in a trepostome bryozoan. Several of these zooecia are visible in tangential sections of Eostenopora guizhouensis (Hu) from the Devonian (Eifelian) Houershan Formation of Houershan, Dushan, southern Guizhou, China. They are broad and occupy the space of two or occasionally three or four normal autozooecia. Some have bridging walls extending partway across the enlarged zooecial chamber. Without serial sectioning, the origin of compound zooecia in E. guizhouensis is debatable. However, the existence of irregular gaps in some zooecial walls leads to the hypothesis that compound zooecia originated from the loss by resorption of the skeletal walls between two normal autozooecia. The bridging walls are interpreted as a response by the bryozoan to restore the integrity of the constituent zooecia. By analogy with the ‘Doppelgänger’ zooids of some modern cheilostome bryozoans, compound zooecia of E. guizhouensis may have housed the lophophores of more than one zooid.     

奥陶纪苔藓动物的多样性演变——兼论苔藓动物的起源

苔藓动物是一类多为海生、滤食性的群体生物。奥陶纪是苔藓动物发生、演化辐射和灭绝的重要时期,也是苔虫礁形成的最早时期。已知最老的化石苔藓动物发现于中国特马豆克晚期。构成苔藓动物基本分类框架的狭唇纲(包括变口目、隐口目、泡孔目和管孔目)和宽唇纲(包括窗孔目和栉口目)也都是在奥陶纪时期逐步形成的,其中,变口目出现于特马豆克期Tr2时间段,在弗洛期和大坪期,多样性较低,但从达瑞威尔期开始,经桑比期至凯迪期,多样性不断增高,并出现辐射。隐口目(特别是"双叶类隐口目苔虫")也经历了与变口目相类似的发展过程,但它首次出现的时间要相对略迟于变口目。这两个目在整个奥陶纪苔藓动物群中一直占据主导地位。泡孔目、管孔目和窗孔目,先后首次出现在弗洛期Fl2时间段、大坪期Dp1和Dp2时间段,但它们在整个奥陶纪期间一直处于低多样性态势。至于栉口目,它首次出现的时间可能更迟,在凯迪期Ka4时间段,犹如昙花一现。苔藓动物的演化在接近奥陶纪末时呈两幕式灭绝,一次发生在凯迪期Ka2时间段(可能相当于塔凯和安斯蒂的"拉夫塞伊灭绝"),另一次发生在赫南特期Hi2时间段(可能相当于塔凯和安斯蒂的"赫南特灭绝")。分子生物学和形态学证据表明,苔藓动物属原口动物,而不是以前长期认为的后口动物,或介于原口动物和后口动物之间的过渡类型;而且,苔藓动物与腕足动物、帚形动物之间没有直接的亲缘关系。苔藓动物可能起源于一种叫原内肛动物的生物,它们的目一级分类单元之间的系统发育关系目前尚未形成共识,本文绘制的谱系图还有待于化石记录的不断补充和分子生物学研究的逐步介入以使其日趋完善。     

Cenomanian cheilostome bryozoans from Devon,England

The Cenomanian witnessed a spectacular evolutionary radiation of cheilostome bryozoans, both in terms of species diversity and morphological disparity. However, Cenomanian cheilostome faunas are inadequately known. Twelve species of cheilostome bryozoans are here described from the Cenomanian Beer Head Limestone Formation of SE Devon, England, a nearshore facies of limestones and sands. Two of the cheilostome species are new – Wilbertopora manubriformis sp. nov. and Foratella cervisia sp. nov. – and five cannot be identified beyond genus level. Syntypes of Foratella forata (d’Orbigny, 1853), the Senonian type species of Foratella Canu, 1900, are illustrated using SEM and a lectotype is chosen. All of the species present are neocheilostomes, which were larval brooders. Compared with the non-brooding malacostegans that dominate pre-Cenomanian faunas, most species have avicularia and extensive frontal walls, features probably adaptive against small predators.     

Genesis and environmental significance of Upper Cretaceous shell concentrations from the Cauvery Basin,southern India

Upper Cretaceous shallow marine calcarenites of the Upper Campanian–Maastrichtian Kallankurichchi Formation from the Cauvery Basin of southeastern India are rich in shell concentrations dominated by large bivalves with minor admixtures of brachiopods, bryozoans, and larger foraminifera. Rarely, these concentrations occur as lenses or pavements, but usually as beds 10 to 200 cm thick. Depending on the dominant skeletal elements, five types of shell concentrations can be distinguished: Isognomon, Pycnodonte, Ceratostreon, inoceramid (?Platyceramus, Cataceramus), and polyspecific concentrations. These shell concentrations occur in various preservational states which reflect the gradual mixing and mechanical destruction of former communities. Analysis of the taphonomic signatures of their components and of the biofabric suggests that storm-induced waves and currents, reduced sediment input, the settling behaviour of taxa, and a high rate of production of biogenic hardparts were responsible, in varying degrees, for the formation of the various shell concentrations. Accordingly they can be classified as storm wave, proximal tempestite, and primary biogenic concentrations. The shell concentrations formed below fair weather wave base in shallow, subtropical, low-stress environments.     

Upper Ordovician bryozoans from the Xiazhen Formation of Yushan,northeastern Jiangxi,East China

The bryozoan fauna from the Xiazhen Formation (Katian, Upper Ordovician) of northeast Jiangxi Province, southeast China is reported here. Seventeen species of bryozoans belonging to fifteen genera and four orders are identified: Homotrypa yushanensis, Homotrypa sp., Prasopora yushanensis, Trematopora sp., Monotrypella sp., Rhombotrypa sp., Orbignyella sp., Constellaria jiangxiensis, Constellaria sp., Stictopora nicholsoni, Trigonodictya parvula, Ptilodictya ensiformis, Stictoporella sp., Pseudopachydictya sp., Nematopora sp., Arthrostylidae sp. indet., and Chasmatoporidae sp. indet. Four of these genera have been reported previously but nine genera (Trematopora, Monotrypella, Rhombotrypa, Orbignyella, Trigonodictya, Ptilodictya, Stictoporella, Pseudopachydictya, and Nematopora), one rhabdomesine and one fenestrate are found for the first time in the Late Ordovician strata of South China. Our palaeogeographical analysis suggests that the bryozoan association is typical for the Katian, which is mostly widespread in Laurentia, Siberia, Baltica and Mediterranean, and displays palaeobiogeographical relationships to the Laurentia–Siberia Province.     

Horizon of the oldest known bryozoans (Ordovician)

Among the six species of fossil bryozoans described by Xia et al. [Xia, F.S., Zhang, S.G., Wang, Z.Z., 2007. The oldest bryozoans: new evidence from the late Tremadocian (Early Ordovician) of East Yangtze Gorges. Journal of Paleontology 81 (6), 1308–1326] from the Fenghsiang Formation of the Chenjiahe section of Yichang and the Guanzhuangping section, Liujiachang Town of Songzi, the Yangtze Gorges, Nekhorosheviella nodulifera occurs in the pristinus Conodont Subzone (lower Subzone of deltifer Conodont Zone) and the five other species are associated with the conodont Paltodus deltifer deltifer and the graptolites Acanthograptus sinensis and A. erectoramus. Based on the conodonts and graptolites, this bryofauna stratigraphically corresponds to the A. sinensis Graptolite Zone or P. deltifer Conodont Zone. The bryofauna is of Tremadocian Age (Early Ordovician) and represents the oldest bryozoans so far as known.     

Serpulids and other calcareous tube-dwelling encrusting polychaetes from the Early Cretaceous Agrio Formation (Neuquén Basin,Argentina)

Serpulids and other related tube-dwelling polychaetes are often ignored when found as fossil remains. They are, however, a widespread and important group today, and abundant literature has been published on them. Knowledge of fossil serpulids is centered on European material, and little has already been done on South American fossil calcareous tubes. In this paper, seven serpulid and sabellid morphotypes are described from the Early Cretaceous marine Agrio Formation of Argentina, revealing a diversity of worms recorded as encrusters on bivalves, ammonites and corals. Sabellids are represented by Glomerula cf. serpentina. Serpulids are represented by two subfamilies: “Serpulinae” includes Mucroserpula mucroserpula, Parsimonia antiquata, Placostegus cf. conchophilus, Propomatoceros semicostatus and P. sulcicarinatus; Spirorbinae is represented by heavily worn tiny coiled tubes assigned to ?Neomicrorbis. Serpulids and sabellids are one of the main components of the mollusk-encrusting fauna recorded in the Agrio Formation, along with small oysters but much more diverse. They are most commonly found as post-mortem encrusters, but some cases of unquestionable living interaction are also found, such as serpulid tubes embedded on coral branches. They are often overgrown by bryozoans, and sometimes by oysters; they frequently occur aggregated.     

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.     

Wachstums- und Knospungsstrategie vonGrammothoa filifera Voigt & Hillmer (Bryozoa,Cheilostomata, Ob. Kreide)

The genusGrammothoa, growing on the interior walls ofThalassinoides burrows in the Maastrichtian Chalk-tuff, has developed a special growth strategy for spatial competition with other encrusting species which has not been previously recorded in bryozoans. The zoarium consists of auto-zooecia, gynozooecia and chains of smaller zooeciules, the latter forming stolon-like outgrowths from the distal edge of the colony. New areas of substratum are explored and colonized by the growth of these zooeciules. At the branching points of the zooeciules, autozooecia and gynozooecia are budded and may coalesce to form the main part of the colony.     

Bryozoans, corals, and microfacies of Lower Eifelian (Middle Devonian) limestones at Kierspe, Germany

The Lower Eifelian Meinerzhagener Korallenkalk (= upper Cultrijugatus Beds) at Kierspe, Sauerland, contains a rich reefal fauna. Eight bryozoan species are described, two of them are new: the cystoporate Fistuliporella kierspensis n. sp. and the trepostome Leptotrypella sophiae n. sp. The bryozoans from the Meinerzhagener Korallenkalk shows distinct similarities to the Lower–Middle Devonian of Spain (Santa Lucía Formation, Emsian–Eifelian), and to the Middle Devonian (Eifelian) of Transcaucasia. The coral fauna comprises five tabulate corals and one rugose coral that document a paleobiogeographic relationship between Central and Eastern Europe and Central Asia. The associated fauna is represented by brachiopods, ostracods, and echinoderms. The studied limestones also commonly contain calcimicrobes represented by three species. The faunal and microfacial characteristics indicate a shallow marine depositional environment just above the storm wave base, with a supposed depth of 20 m, within the photic zone. The nutrient regime was at least a mesotrophic. The upper boundary of the Cultrijugatus Beds coincides with the Chote?-Event that strongly affected brachiopods, whereas corals and bryozoans were insensitive to this event.     

Taphonomy and ichnology: tools for interpreting a maximum flooding interval in the Berriasian of Tlemcen Domain (Western Tellian Atlas,Algeria)

During the Middle-Late Berriasian, a long-term climatic and eustatic change occurred, documented in the literature. However, data from the northern Gondwana paleomargin are scarce. This research analyzes the Lamoricière Clay Formation at the Ouled Mimoun section, focusing on fossil assemblages and using taphonomic and ichnological aspects to interpret a transgressive–regressive cycle. The section starts with mudstones and oolitic grainstones representing shallow-water environments in the top part of the Ouled Mimoun Marly Limestones Formation (Upper Tithonian p.p. to lowermost Berriasian). The base of the Lamoricière Clay Formation is characterized by a high clay content but was still deposited in shallow water, as indicated by the record of the ostracod Asciocythere, dasyclad green algae, and the sponge Cladocoropsis. The subsequent record of fossil-rich calcareous beds at the beginning of the Upper Berriasian (Boissieri Zone) with ammonoids and calpionellids is congruent with an increase in water depth. The sedimentation rate in the Late Berriasian was reduced, as indicated by the increment of fossil remains and trace fossils. Ammonoid moulds show taphonomic features pointing to long-lasting exposure on the sea floor prior to burial with corrasion and encrustation by sessile organisms such as serpulids, thecideidinids, and bryozoans. During calm periods, crustaceans and worms intensely burrowed the sea floor. The record of Thalassinoides and Rhizocorallium indicates bottom conditions ranging from soft to firm. The low sedimentation rate and sediment by-passing probably favored early lithification. The increasing carbonate content as well as decreasing sedimentation rate is compatible with the maximum distance to emerged areas during maximum flooding. High-energy events, probably related to storms, favored the exhumation and extreme corrasion of ammonite moulds and trace fossils. In the resulting substrate, limonitic films developed and encrusting organisms proliferated (serpulids, bryozoans, and thecideidinids), colonizing both the bottom surface (hardground) and exhumed moulds of ammonoids and Thalassinoides. The uppermost 0.7 m of the section represents the return to shallow conditions, with increasing sedimentation rate and terrigenous detrital content, along with the disappearance of hemipelagic forms (ammonoids); hence it is interpreted as having developed at the beginning of a regressive context.     

The infaunal echinoid Micraster: Taphonomic pathways indicated by sclerozoan trace and body fossils from the Upper Cretaceous of northern Spain

Micraster echinoid fossils are common in the Upper Cretaceous Olazagutía Formation of northern Spain. Tests frequently record sclerobiont signatures (including bioerosion and encrustation), left by reaction and/or coaction phenomena. Among bioerosion structures, Oichnus simplex, O. paraboloides, O. ichnosp. A, Trypanites solitarius, Rogerella ichnosp. indet., Centrichnus cf. eccentricus, Maeandropolydora ichnosp. indet. and fungal microborings are found, as well as pits and fractures. As for sclerozoan body fossils, bivalves (Dimyidae, Anomiidae, Plicatulidae and other Pectinacea), polychaete annelids (serpulids and spirorbids), lituolid foraminiferans (Haddoniidae and Coscinophragmatidae) and bryozoans (cheilostomate ones and others undetermined), as well as other less common groups, have been identified. Taphonomic paths followed by Micraster tests are analysed, based on conservation state and degree of colonisation and sedimentary filling. This allows to distinguish between accumulated fossils and non accumulated ones (including resedimented and reelaborated ones).     

Conodont biostratigraphy of the Upper Devonian-Lower Carboniferous Shahmirzad section, central Alborz, Iran

The conodont fauna from the Devonian-Carboniferous Shahmirzad section, located in the Central Alborz Mountains (North Iran), have been studied mainly for biostratigraphic purposes. Some levels were barren of conodonts, whereas others yielded a not very abundant, but quite differentiated fauna. No conodonts have been found from the mainly terrigenous and shaly Geirud Formation, whereas representative of genera Bispathodus, Clydagnathus, Gnathodus, Hindeodus, Mehlina, Polygnathus, Protognathodus, Pseudopolygnathus and Siphonodella have been collected from the mainly calcareous overlaying Mobarak Formation. The fauna allowed to discriminate five biointervals, from the sulcata Zone to a “Lower typicus - anchoralis-latus interval” in the central part of the section, while the lower and upper parts cannot be zoned on the basis of conodonts. This paper is the first report on lowermost Carboniferous conodonts from the Mobarak Formation in central Alborz.     

Species- and site-specific bacterial communities associated with four encrusting bryozoans from the North Sea, Germany

Epi- and endozoic bacterial communities associated with four bryozoan species from the Jade (North Sea, Germany) were investigated by the combined application of molecular tools and electron microscopic visualisation of zooids. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments of associated bacteria displayed specific bacterial community profiles in the examined species Aspidelectra melolontha, Conopeum reticulum, Electra monostachys and Electra pilosa. Actual bacterial epibiosis was only observed on C. reticulum whilst the other bryozoans under investigation were largely free of microbial epibionts. These observations indicated that bryozoan-associated bacteria identified by molecular methods originated from internal cavities of bryozoan zooids. Cluster analysis of DGGE band patterns revealed species-specific bacterial communities in A. melolontha, E. monostachys and E. pilosa. Bacteria associated with C. reticulum were seemingly influenced by site-specific parameters. A comparison of bacterial community profiles between reference and invertebrate surfaces allowed for an interpretation of conspicuous group-specific differences. Operational taxonomic units (OTUs) obtained from a single set of bryozoan replicates that were absent on the inorganic reference samples (mussel shells) were hypothesized to be favourable endobionts. Contrary, OTUs present in the references but absent in bryozoan samples could be assumed to stem from bryozoan-specific defenses against ubiquitous bacterial colonizers. Although there was no experimental evidence for a mutual relationship between prokaryotes and their eukaryotic bryozoan hosts, this study demonstrated that in three out of four bryozoans under investigation associated bacterial communities were characteristically shaped by host attributes.     

Skeletal Ultrastructure in the Cyclostome Bryozoan Hornera

Abstract Scanning electron microscopy of calcified walls in two species of the cyclostome bryozoan Hornera has revealed previously undescribed details of skeletal morphology and growth. The calcitic interior walls of both H. robusta MacGillivray and H. squamosa Hutton have a laminated structure. Walls are extended at distal growing edges where the formation of new crystallites is concentrated and wall fabric is nacreous or semi-nacreous. New crystallites are seeded on the surface of existing crystallites as six-sided rhombs. At the centres of the rhombs in H. robusta there are often three ‘spikes' which point towards alternate sides of the rhomb. Screw dislocations resulting in spiral overgrowths are also common at these distal wall edges. Wall thickening occurs further proximally where walls develop a regularly foliated structure of imbricated laths growing towards the colony base. Although often thought to be ubiquitous in cyclostomes, the division of walls into three layers (an inner, primary layer flanked on both sides by secondary layers) is absent in Hornera. Wall ultrastructure contrasts strongly with the lamellar–fibrous–lamellar structure recently described from cinctiporid cyclostomes. The c-axes of the crystallites are orientated perpendicular to the wall surface in Hornera, unlike cinctiporids in which they are orientated within the plane of the wall. Apparent similarities in ultrastructure suggest that Hornera may provide a good model for wall growth in extinct trepostome bryozoans.     

Brachypotherium (Perissodactyla,Rhinocerotidae) from the late Miocene of Samburu Hills,Kenya

Several isolated cheek teeth and mandibular specimens of Rhinocerotidae (Mammalia, Perissodactyla) from the upper Miocene Namurungule Formation in Samburu Hills, Kenya, are redescribed. Previously, these specimens had been identified as Chilotheridium pattersoni, Chilotheridium sp., Paradiceros mukirii, and Paradiceros sp. They are reidentified here as documenting the genus Brachypotherium based on their bucco-lingually broad molariform upper premolars with short crochet and flattened buccal walls on both upper and lower molars, the latter having a shallow external groove. Comparisons with other Brachypotherium species suggest that the present specimens belong to Brachypotherium sp. cf. B. minor. The presence of Brachypotherium in the Samburu Hills, at ca. 9.5 Ma, is concordant with the paleoenvironment (presence of lacustrine and river environments) known for this locality during the early late Miocene.     

Early Triassic bivalves from the Feixianguan Formation in Xingyi,Guizhou and the Ximatang Formation in Qiubei,Yunnan (southern China)

Based on newly collected materials from the Lower Triassic Feixianguan Formation of Xiongwu section in Xingyi, Guizhou and the Ximatang Formation of Ximatang section in Qiubei, Yunnan, southern China, nine species belonging to seven genera are described. Two bivalve assemblages are recognized and regionally correlated in South China. The bivalve assemblage from the Feixianguan Formation of Xiongwu exhibits a higher diversity including seven species belonging to seven genera: Claraia griesbachi, Leptochondria virgalensis, Entolium (Entolium) microtis, Towapteria scythicum, Bakevillia exporrecta, Bositra sp., and Unionites? fassaensis. In contrast, the bivalve assemblage from the Ximatang Formation of Ximatang has a much lower diversity, consisting of only two species, i.e., Claraia griesbachi and Claraia radialis. Additionally, C. griesbachi and C. radialis, as the most common species of Claraia in the Early Triassic, are revised.     

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。