Chondrichthyan‐like scales from the Middle Ordovician of Australia

Abstract: Microvertebrate sampling of the Stairway Sandstone (Darriwilian, Middle Ordovician, central Australia) has yielded scales that are chondrichthyan‐like in their overall construction, and Tantalepis gatehousei gen. et sp. nov. is erected here to describe these specimens. Tantalepis gatehousei gen. et sp. nov. is the stratigraphically oldest microsquamous taxon described thus far, and the ‘shark‐like’ appearance of the scales may extend the chondrichthyan lineage back into the Middle Ordovician. The presence of ‘shark‐like’ scales in the fossil record some 50 myr prior to the first articulated chondrichthyan body fossils and 44 myr before the first clearly identifiable chondrichthyan teeth suggests there is a considerable scope for the recovery of articulated specimens with which to document the early history of crown gnathostomes. Traditional hypotheses of phylogenetic relationships among early jawed vertebrates were recently challenged by the proposal of a radically different tree topology. However, the development of a new data set specifically addressing scale‐based characters is required before taxa such as Tantalepis, that are based upon disarticulated remains alone, can be firmly placed within the emerging, revised, evolutionary narrative.     

Bryozoans as taphonomic engineers,with examples from the Upper Ordovician (Katian) of Midwestern North America

A combination of encrusting calcitic bryozoans and early seafloor dissolution of aragonitic shells recorded in the Cincinnatian Series of the upper Midwest of North America allowed the preservation of abundant moulds of mollusc fossils bioimmured beneath the attachment surfaces of the bryozoans. We here call this preservational process ‘bryoimmuration’, defined as a bryozoan‐mediated subset of bioimmuration. The bryozoans moulded very fine details of the mollusc shells, usually with more accuracy than inorganic sediment moulds. Most of the bryozoans are heterotrypid trepostomes with robust low‐Mg calcite skeletons. The molluscs are primarily bivalves, gastropods, nautiloids and monoplacophorans with their originally aragonitic shells now dissolved. Many of the encrusting bryozoans are so thin and broad that they give the illusion of calcitic mollusc shells clinging to the moulds. Some molluscs in the Cincinnatian, especially monoplacophorans and epifaunal bivalves, would be poorly known if they had not been bryoimmured. Unlike internal and external moulds in sediment, bryoimmured fossils could be transported and thus record aragonitic faunas in taphonomic assemblages (e.g. storm beds) in which they would otherwise be rare or absent. In addition, bryoimmurations of aragonitic shells often reveal the ecological succession of encrustation on the shells by exposing the earliest encrusters and borings that were later overgrown. Bryoimmuration was common during the Late Ordovician because the calcite sea at the time quickly dissolved aragonitic shells on the seafloor before final burial, and large calcitic bryozoans very commonly used molluscs as substrates. Bryoimmuration is an important taphonomic process for preserving aragonitic faunas, and it reveals critical information about sclerobiont palaeoecology. Several Cincinnatian mollusc holotypes are bryoimmured specimens. Bryozoans involved in bryoimmuration enhance the preservation of aragonitic fauna and thus act as taphonomic engineers.     

Silicified Upper Ordovician trilobites from Pai‐Khoi,Arctic Russia

Abstract: A collection of silicified trilobites extracted from samples obtained by F. Nansen from the Upper Ordovician of Khabarovo, Pai Khoi, Russian Arctic is dominated by two new species of the proetide Lasarchopyge, a genus known hitherto only from the Argentine Precordillera. Comparison of Lasarchopyge with Scharyia reveals a range of common characters that support inclusion of both genera in the same family. The rest of the fauna comprises a metagnostid (Trinodus elspethi), an asaphid (Isotelus sp.), two remopleuridids (Remopleurides cf. caelatus and R. sp. nov. A), an aulacopleurid (Harpidella triloba), a lichid and an odontopleurid (Apianurus cf. barbatus), the last two being represented by very fragmentary material. T. elspethi, H. triloba, R. cf. caelatus and A. cf. barbatus are common to or closely resemble taxa from the Edinburg Formation, Virginia. Closely related taxa are present also in the Esbataottine Formation, NW Territories, Canada, and in the Albany Group, Girvan district, Scotland. All of these occurrences are of early Caradoc (Sandbian) age, and most lay at palaeolatitudes of 20°–30° south; all are interpreted as having been deposited on the outer shelf, which is consistent with their distribution.     

Trilobite biofacies and sequence stratigraphy: an example from the Upper Ordovician of Oklahoma

There have been surprisingly few empirical investigations of the fundamental principle that the architecture of depositional sequences exerts considerable control on observed patterns of faunal distribution and replacement. In this paper, we examine trilobite associations in two sequences of the Upper Ordovician (Sandbian) Bromide Formation of southern Oklahoma. Cluster analysis and ordination of genus abundance data identified five lithofacies‐related biofacies that are also differentiated by diversity patterns. Biofacies of the transgressive system tract (TST) of successive sequences are more similar to each other than they are to biofacies in the highstand systems tract (HST) of the same sequence. This similarity likely records dominance of large, robust convex sclerites in taphonomically degraded samples from condensed, strongly winnowed grainstone and rudstone. Horizons with articulated exoskeletons of isoteline trilobites preserved by obrution deposits occur most commonly in the early HST and record behavioural aggregations. Grainstone and rudstone of the later HST are less winnowed than those of the TST and show less fragmentation and sorting of sclerites. These changes in taphonomic conditions preserve ecological patterns more clearly. In most biofacies, rarefied alpha diversity (samples) and gamma diversity (biofacies) of middle‐ and outer‐ramp HST deposits are greater than in the TSTs, and biofacies replace each other down ramp. Diversity patterns do not agree with model predictions and other data sets that indicate low beta and high alpha diversity in the TST, likely because of taphonomic degradation. Vertical replacement of biofacies is expressed by the appearance of peritidal facies in which trilobites are rare. Biofacies shifts also characterize sequence boundaries and are most profound in the inner‐ramp successions characterized by sharp facies offsets. Comparison with bathymetrically similar deposits in the Taconic foreland basin showed similar diversity trends along environmental gradients, with some differences in shallow‐water settings attributed to taphonomic differences.     

The graptolite correlation of the North American Upper Ordovician Standard

The North American Upper Ordovician reference standard, the Cincinnatian Series, contains rich shelly microfossil faunas in its type area in the Cincinnati Region but graptolites are uncommon in most of its shallow-water calcareous sediments. Consequently, the graptolite correlation of this key sequence has remained uncertain, in part, even controversial. A review of both previously published recently discovered graptolite Occurrences in the type Cincinnatian, combined with data from the important graptolite successions in Oklahoma New York-Quebec, has not only clarified the graptolite correlation of the Cincinnatian but also added new data on the morphology taxonomy, the vertical horizontal distribution, of several taxa. The information now at hand indicates that the Edenian Stage correlates with the C. spiniferus Zone, the Maysvillian Stage with the C. pygmaeus lower middle P. manitoulinensis Zone, the Richmondian Stage with the upper P. manitoulinensis , the D. complanatus , possibly part of the C. inuiti Zone. Comparison between graptolite conodont biostratigraphic evidence reveals no apparent conflict. Correlations are proposed between Upper Ordovician North American stages, graptolite conodont zones, successions in Texas, Oklahoma, Sweden, European graptolite zones, British series.     

An opportunistic Upper Ordovician trilobite assemblage from Missouri

The trilobite Ampyxina bellatula (Savage) occurs in monospecific accumulations within dolomitic strata of the shaly Upper Ordovician Maquoketa Group of northeastern Missouri. A dolomitic stratum containing 97 complete individuals and considerable amounts of pyrite exhibited no associated benthic megafauna. The strata appear to be equivalent to the Scales Formation of the Maquoketa Group of northern Illinois and eastern Iowa which have been interpreted as having been deposited in a muddy environment with severe circulation restrictions. The presence of the monospecific trilobite association in what otherwise would be an unfossiliferous stratigraphic sequence is interpreted as being the result of opportunistic strategy by this trilobite in a resource-rich unstable environmental setting. The association was apparently cat-astrophically buried, thus preserving the age structure of the holaspid population. A size-distribution histogram of the holaspid population indicates that reproduction may have occurred in periodic bursts with lesser reproductive events occurring during the intervening periods. Holaspid survivorship information indicates that mortality was low during the early holaspid stage and increased with age. Anomalous single bed trilobite accumulations of various age rocks have been documented by numerous authors. These may in part be analogous to the Ampyxina occurrence in the Maquoketa Group of Missouri, and be attributable to opportunistic strategies.     

A 17‐element conodont apparatus from the Soom Shale Lagerstätte (Upper Ordovician), South Africa

Abstract:  Natural assemblages of a new conodont taxon, Notiodella keblon, from the Upper Ordovician Soom Shale Lagerstätte of South Africa contain 17 elements. This is the first time that a 17‐element apparatus plan has been unequivocally demonstrated in conodonts. The apparatus comprises paired P₁, P₂, P₃, M, S₁, S₂, S₃ and S₄ elements and an unpaired, axial S₀ element and provides a new template for use in the reconstruction of apparatuses from the collections of dispersed elements, particularly for those with icrion‐bearing P₁ elements and perhaps for other balognathids.     

Tentaculitoid affinities of the tubeworm-like fossil Tymbochoos sinclairi (Okulitch, 1937) from the Ordovician of North America

Tymbochoos sinclairi (Okulitch, 1937) has a laminar tube structure and pseudopuncta similar to the tentaculitoids. This suggests that Tymbochoos belongs to the Tentaculitoidea Bou?ek, 1964.     

Katian (Upper Ordovician) conodonts from Wales

Middle and upper Katian conodonts were previously known in the British Isles from relatively small collections obtained from a few localities. The present study is mainly based on 17 samples containing more than 17 000 conodont elements from an approximately 14‐m‐thick succession of the Sholeshook Limestone Formation in a road cut near Whitland, South Wales, that yielded a diverse fauna of more than 40 taxa. It is dominated by representatives of Amorphognathus, Aphelognathus/Plectodina and Eocarniodus along with several coniform taxa. Representatives of Decoriconus, Istorinus and Sagittodontina are reported from the Ordovician of UK for the first time. The fauna is a typical representative of the British Province of the Atlantic Realm and includes a mixture of taxa of North American, Baltoscandic and Mediterranean affinities along with pandemic species. Based on the presence of many elements of Amorphognathus ordovicicus and some morphologically advanced specimens of Amorphognathus superbus, the Sholeshook Limestone Formation is referred to the lower A. ordovicicus Zone. Most of the unit is also coeval with Zone 2 of the Cautleyan Stage in the British regional stage classification, and stage slice Ka3 of the middle Katian Stage in the global stratigraphical classification, an age assignment consistent with data from trilobites, graptolites and chitinozoans. The unusually large collection of M elements of Amorphognathus provides insight into the complex morphological variation in this element of some Katian species of this genus. The Sholeshook conodont fauna is similar to those of the Crûg and Birdshill limestones, but differs in several respects from the slightly older ones from the Caradocian type area in the Welsh Borderland. Although having some species in common, the Sholeshook conodont fauna clearly differs from coeval Baltoscandic faunas and is even more different in composition compared with equivalent North American Midcontinent faunas.     

Probing the deep shelf: a Lagerstätte from the Upper Ordovician of Girvan, southwestern Scotland

A deep‐water Konservat Lagerstätte from the lower Caradoc (Sandbian) at Girvan is dominated by the trilobite Diacanthaspis trippi, the carpoids Anatifopsis n. sp.? and a new genus of ctenocystoid together with the polyplacophoran Solenocaris solenoides and the brachiopod Onniella williamsi. Most of these are multi‐element organisms, with many specimens preserved in an articulated state in finely laminated rocks, indicating minimal disturbance and suggesting that the fauna is largely an in situ association. It contains few of the species known from other deep‐water sites of similar age at Girvan which contain diverse assemblages of trilobites and brachiopods absent from the Lagerstätte. The taphonomy of the site indicates preservation by rapid burial followed by early diagenesis under dysaerobic conditions. It provides a ‘taphonomic window’ on otherwise unknown faunas from distal shelf facies on the Ordovician Laurentian margin, and, moreover, is an important reminder of the hidden biodiversity that resided in thin‐shelled, multi‐element organisms.     

新疆柯坪和甘肃平凉上奥陶统底部附近的牙形刺

新疆柯坪大湾沟和甘肃平凉官司庄剖面是Nemagraptusb gracilis带及上奥陶统底界的重要剖面,研究这两剖面的牙形刺具有十分重要的意义。本文描述了采自新疆柯坪大湾沟和甘肃平凉官司庄剖面上奥陶统底界附近的牙形刺共13属18种。     

Foliomena Fauna (Brachiopoda) from the Upper Ordovician of Sardinia

The late Ordovician brachiopod assemblage from Sardinia is one of the youngest members of the deep-water Foliomena fauna and is characterized by the following core taxa: Christiania , Cyclospira , Dedzetina and Foliomena . The fauna also contains Epitomyonia , Leangella , Glyptorthis and Skenidioides , which are more typical of shallower-water environments during the late Ordovician but occupied deeper-water niches during the Silurian following the termination of the Foliomena fauna. The suprafamilial placement of the family Chrustenoporidae is discussed and the new species Dedzetina serpaglii and Leangella ( Leangella ) fecunda are established. In common with many mid-Ashgill Foliomena faunas the Sardinian assemblage shows significant differences from other faunal developments of this type, reflecting its geographical position and shallower water conditions than those of the classic early Ashgill Foliomena faunas. The brachiopods occur with abundant trilobites belonging to a variant of the cyclopygid fauna. The faunas developed on part of a complex of microcontinents derived from peri-Gondwana during the Ordovician.     

Cryptostomid Bryozoans From The Sassito Formation,Upper Ordovician Cool‐Water Carbonates of the Argentinean Precordillera

Abstract: Two new bryozoan species are described from the Upper Ordovician Sassito Formation of the Argentinean Precordillera: Moyerella  spinata sp. nov. and Phylloporina  sassitoensis sp. nov. The bryozoans are found in cool‐water carbonates. The Silurian genus Moyerella is reported the first time in the Ordovician, showing palaeobiogeographic connections with Estonia and Siberia.     

Non-calcified warm-water marine macroalgae from the Ordovician strata of Spiti,Tethys Himalaya,India

The calcareous siltstones within the Ordovician section of the Takche Formation near Takche, Spiti region of Tethyan Himalaya, India, contain numerous specimens of non-calcified marine macroalgae in association with brachiopods, gastropods, tentaculitoids, and few trace fossils. The algal remains, representing five genera, are preserved as black or dark brown carbonaceous compression fossils, interpreted as warm-water marine macroalgae, namely, Inocladus sp., Callisphenus? sp., Algites sp. (siphonous algae), Fisherites sp., and Mastopora sp. (non-siphonous). Callisphenus is characterised by a radially symmetrical short pyriform thallus, with a central axis surrounded by short laterals whereas Inocladus sp. is characterised by an unsegmented simple thallus with internal parallel medullary siphons and cortical tubes. These algal remains, probably transported from a more near-shore living niche, co-occur with Cyclocrinitids, Tentaculitoids tube worms, trace fossils and brachiopods, suggesting that deposition of the studied units took place in low energy hydrodynamic conditions influenced by intermittent storm events. The study represents the first diversified macroalgal records from the Ordovician strata in the Tethyan realm of Indian subcontinent.     

Late Cretaceous Mammal Tracks from North America

Mammal tracks from the latest Cretaceous (Campanian-Maastrichtian) of Colorado are described as Schadipes crypticus ichnogen. et ichnosp. nov., on the basis of material from the Laramie Formation in Golden, eastern Colorado. This ichnospecies, and a closely related form (Schadipes sp.) from the Mesaverde Group of western Colorado, represent the only mammal tracks so far identified from the Upper Cretaceous. A possible mammal track from North Africa (Agadirichnus elegans) was originally attributed to a lizard/lacertilian. Other purported Lower Cretaceous mammal tracks are based on isolated specimens of materials that are dubious or as yet undescribed in detail. Morphologically, Late Cretaceous mammal tracks resemble those of some modern rodents. However, based on the dominant mammalian elements of faunas at that time they are probably of marsupial or multituberculate affinity.     

黔北上奥陶统宝塔组头足类多样性初探*

上奥陶统宝塔组(桑比阶–凯迪阶)是华南分布广泛的标志性地层单元, 以发育特殊的网纹状灰岩并产出大量头足类化石为特征。黔北桐梓县尧龙山地区的宝塔组厚度较大, 出露极好, 产出数量丰富、保存精美和特征典型的头足类化石。本文在研究区酒店垭、集镇采坑和天域极地3个宝塔组剖面采集到大量原域埋藏的头足类化石, 共8属11种及少量属种未定类型, 以直形壳或盘形壳、体管很小且适合远洋深水游泳的类型为主, 整体上符合扬子台地深水陆棚Sinoceras–Michelinoceras–Disoceras生物相特征。基于壳体扩大率、壳径与体管直径比、气室高与隔壁颈长比、隔壁下凹度、壳径与气室高比等参数变量的主成分分析表明, 在外部特征不显著的情况下, Sinoceras和Michelinoceras的直观差别是壳体扩大率, 而Michelinoceras属不同种的差异主要体现在气室高与隔壁颈长之比, 其他特征的区分度并不明显。层面上单位面积的化石定量统计显示, 尧龙山地区宝塔组中头足类的多样性较高, 并以Sinoceras和Michelinoceras具有极高的个体丰度为特征。扬子板块在奥陶纪桑比期–凯迪期之交处于高水位的陆表海环境, 栖息环境均一化和生态系统复杂化可能是促进该时期头足类动物的复苏和多样性演化的重要原因。     

New species of stromatoporoidea from the Upper Ordovician and Silurian of the Subpolar Urals

Stromatoporoidea are widespread in the Upper Ordovician and Silurian beds of the Kozhim River (western slope of the Subpolar Urals). Five new species Cystostroma prodigiosum sp. nov., Stylostroma flabellatum sp. nov., Labechiina arguta sp. nov., Ecclimadictyon faveolatum sp. nov., and Araneosustroma astroplexum sp. nov. are described.     

The trace fossil Sinusichnus from the Upper Ordovician of Anticosti Island,eastern Canada

Branched, sinusoidal burrows assigned to Sinusichnus cf. seilacheri Knaust et al. 2016; occur in Upper Ordovician (Hirnantian) carbonates on Anticosti Island. These are abundant and monospecific at the base of the Oncolite Bed of the uppermost Ellis Bay Formation, marking a regional discontinuity surface during the multiphase Ordovician mass-extinction event. In contrast to Mesozoic and Cenozoic records of Sinusichnus, commonly attributed to the activity of decapod and isopod crustaceans, the burrow systems from Anticosti Island were probably produced by other arthropods of unknown affinity. A combined dwelling, locomotion and feeding behaviour of their trace maker is assumed. This is the oldest record of the ichnogenus Sinusichnus, previously only known since the Triassic, and its first evidence from North America.