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We describe early Tremadocian (Kainella meridionalis Biozone) cephalopods from the Cordillera Oriental, Jujuy, NW Argentina. They consist of numerous small specimens collected at the Quebrada de Arenal, Trancas section, near the town of Tilcara, in the Alfarcito Member of the Santa Rosita Formation. All but three specimens were assigned to a new species of Ellesmeroceras (Family Ellesmeroceratidae), E. humahuacaensis sp. nov., based on its slightly endogastric curvature, the characteristics of the siphuncle and chambers dimensions. Micro CT scanning of one specimen aided in the description of the apex and facilitated the construction of a 3D model of the species. A single, similar specimen was assigned to Ellesmeroceras sp. pending the availability of additional material. Two specimens differ from the rest, being exogastric with a lower angle of expansion. They are tentatively assigned to Bassleroceras sp. This material indicates that Cambrian and early Tremadocian cephalopods are not as different as previously thought. “Diversification” and “extinction” events during the late Cambrian may be attributed to taxonomic “over-splitting” and taphonomic and/or sampling biases, respectively. These specimens are currently the oldest recorded in the Central Andean Basin and of West Gondwana, and probably represent the first migration of cephalopods into the region, when the water column was still poorly colonized. During the middle Tremadocian, subsequent immigrations and originations of several cephalopod orders accounted for a rise in diversity and expansion into new niches during this interval. Some of these taxa persisted into the middle Floian, at which time, a second increase in diversity is recorded. Ellesmeroceras humahuacaensis sp. nov. is interpreted as a sub-vertical nektobenthic organism.

The Lower Ordovician Fezouata Shale is renowned for its exceptionally-preserved euarthropod fossils including numerous species of trilobites, some of which show remains of appendages and traces of the digestive system. Herein, we describe the early developmental stages of at least nine trilobite species from the Tremadocian strata of the Fezouata Shale, namely Platypeltoides magrebiensis , Nileus deynouxi , Symphysurus ebbestadi , Asaphellus sp., Megistaspis (Ekeraspis) hammondi , Orometopus sp., Anacheirurus adserai , Bavarilla zemmourensis , Indiligens sp., and several specimens of undetermined protaspides. This study considerably expands our knowledge of the development of early Ordovician trilobites. The preservation of appendages in the early stages of N. deynouxi and S. ebbestadi , and remains of the digestive tract in the latter species, suggests that some immature trilobites had similar morphology and anatomy as the adult individuals. Early developmental stages of Indiligens sp. might have fed and/or hidden on graptolites and demosponges. The extraordinarily large size of the early post-embryonic stages of P. magrebiensis , S. ebbestadi , Orometopus sp., Asaphellus sp., and undetermined protaspides suggests that these trilobites might have hatched from yolk-rich eggs. The presence of several trilobite species with notably large post-embryonic stages in the Fezouata Shale might be explained by seasonal or low productivity in the high-latitude margin of Gondwana. [ABSTRACT FROM AUTHOR]

Graptolites from the early Tremadocian Anisograptus matanensis Biozone are identified from east-central Sonora, northwestern Mexico, within a carbonate-shelf succession deposited on the southwestern continental shelf margin of Laurentia. This is the second occurrence of typical anisograptid graptolites in Mexico, after its original record in the Oaxaca area, which belongs to a Gondwana-related paleogeographical realm. The graptolites from Sonora represent the second global occurrence of any member of the Rhabdinopora flabelliformis group in the Ordovician equatorial shelf region.

Tremadocian highly metalliferous black shales and associated grey shales from the Aseri PH012B drill core (NE Estonia) in the innermost part of the Baltic Palaeobasin were targeted to record their nitrogen and organic carbon isotope variance combined with the total organic carbon and total nitrogen record. The obtained molar C/N ratios of black shales from 26 to 52 indicate a considerable loss of N compared to primary biomass. The recorded δ15N values from â2.5 to 0.2â° likely evolved due to isotopic fractionation related to N2 fixation by primary producers, superimposed by later anoxic ammonium oxidation processes within the uppermost sediments. The high net primary productivity, which controlled the accumulation of organic-rich shallow-water complexes, was fuelled by the internal cycling of P in the sea basin and combined with intensive N exchange between marine and atmospheric pools.

The Erdaopuzi section in the Baishan area of Jilin Province, northeast China, contains abundant late Tremadoc graptolites. However, there are some taxonomic controversies regarding the characters of the hand specimens that are difficult to identify. In this paper, we present our restudy of isolated graptolites from acid residue and discuss the taxonomic problems of the subgenus Clonograptus (Neoclonograptus) Zhao and Zhang. Four genera and six species were identified, including Adelograptus tenellus (Linnarsson), Ancoragraptus gracilis (Zhao and Zhang), Dictyonema sp., Psigraptus jacksoni Rickards and Stait, Psigraptus lenzi Jackson, Psigraptus arcticus Jackson. According to the significant evolution of morphological characters, two graptolite zones (from bottom to top) can be identified in ascending order in the study area, i.e. Adelograptus Zone and the Psigraptus Zone.

Solutans are relatively common members of echinoderm assemblages in the Saint-Chinian Formation (upper Tremadocian) of the Montagne Noire (France). The revision of all available material confirms that most specimens can be assigned to Minervaecystis vidali, which is here reconstructed for the first time. The occurrence of Plasiacystis mobilis is evidenced based on a single, well-preserved dististele. The interpretation of the small-sized individual as a putative dendrocystitid is rejected: it corresponds to a juvenile specimen of M. vidali. Early Ordovician solutans from the Montagne Noire partly fill the gap between Laurentian midâlate Cambrian syringocrinids and Avalonian-Gondwanan EarlyâMiddle Ordovician taxa.

We describe early Tremadocian (Kainella meridionalis Biozone) cephalopods from the Cordillera Oriental, Jujuy, NW Argentina. They consist of numerous small specimens collected at the Quebrada de Arenal, Trancas section, near the town of Tilcara, in the Alfarcito Member of the Santa Rosita Formation. All but three specimens were assigned to a new species of Ellesmeroceras (Family Ellesmeroceratidae), E. humahuacaensis sp. nov., based on its slightly endogastric curvature, the characteristics of the siphuncle and chambers dimensions. Micro CT scanning of one specimen aided in the description of the apex and facilitated the construction of a 3D model of the species. A single, similar specimen was assigned to Ellesmeroceras sp. pending the availability of additional material. Two specimens differ from the rest, being exogastric with a lower angle of expansion. They are tentatively assigned to Bassleroceras sp. This material indicates that Cambrian and early Tremadocian cephalopods are not as different as previously thought. “Diversification” and “extinction” events during the late Cambrian may be attributed to taxonomic “over-splitting” and taphonomic and/or sampling biases, respectively. These specimens are currently the oldest recorded in the Central Andean Basin and of West Gondwana, and probably represent the first migration of cephalopods into the region, when the water column was still poorly colonized. During the middle Tremadocian, subsequent immigrations and originations of several cephalopod orders accounted for a rise in diversity and expansion into new niches during this interval. Some of these taxa persisted into the middle Floian, at which time, a second increase in diversity is recorded. Ellesmeroceras humahuacaensis sp. nov. is interpreted as a sub-vertical nektobenthic organism. [ABSTRACT FROM AUTHOR]

Schizambon is one of the earliest and most distinctive genera in the Order Siphonotretida. However, current knowledge of siphonotretide phylogeny and early evolution requires understanding of their earliest ontogeny. In this study, the new species Schizambon tongziensis from the Tungtzu Formation at Honghuayuan section in Guizhou Province, South China is described; it is also the first record of Schizambon in South China. The new well‐preserved specimens shed light on the ontogeny, palaeobiogeographical distribution, phylogeny and early evolution of siphonotretide brachiopods. Characters of metamorphic shells on both valves, outlined by distinct halos, show that Schizambon had a planktotrophic 'paterinide‐type' larva, typical of many early Palaeozoic brachiopods. Based on the newly obtained data it is inferred that the free‐swimming larva of Schizambon settled directly on the ventral side of the body, and this type of ontogeny is probably true for other siphonotretides. The divergence of Schizambon from the main siphonotretide lineage probably happened prior to the Guzhangian Age, well before the occurrence of major biodiversification within the order. [ABSTRACT FROM AUTHOR]

By compiling data from literature and unpublished reports a more detailed description is presented on the geographical and stratigraphic distribution of the Alum Shale Formation (ASF) and correlateable units on the East European Platform. In the northern part of Gotland, downfaulted patchy beds of the ASF indicate a former wider extension of the formation. Lower Ordovician (Tremadocian) examples of downfaulted patchy beds are the contemporaneous Sepopol and Nivenskaya formations in northeastern Poland and the Kaliningrad area, as well as the Salantai Formation in the east Baltic area. It is indicated that Furongian-Tremadocian beds, contemporaneous with the Kallavere, Türisalu, Tosna and Koporye formations, in the area of northern Estonia and the northwestern part of the Moscow Basin, extended to the Gotland and the South Bothnian Basin areas. South of Gotland, in the Swedish sector of the Baltic Basin, drill cores show evidence of tectonic movements through the presence of erosional surfaces indicating occasional subaerial exposure. In this region, variations in the areal extent and thickness of the ASF and coeval formations are suggested to be the result of epeirogenic and tectonic block movements. Tremadocian ASF is also indicated to be present south of Gotland. On Gotland, at least 5 m of the ASF is presumed to have been eroded. The Moscow Basin contains 19 m of dark shales (Koporye Formation) which is significantly thicker than in surrounding areas. [ABSTRACT FROM AUTHOR]

Well‐preserved graptolites of the genus Kiaerograptus are first reported from the upper Tremadocian Yinchupu Formation in the Nanba section, Yiyang, Hunan Province, South China, including four species, i.e., Kiaerograptus lauzonensis (Erdtmann, 1966), Kiaerograptus stoermeri (Erdtmann, 1965), Kiaerograptus cf. supremus? Lindholm, 1991, and Kiaerograptus sp., which are robust in form. Based on these new specimens, the Kiaerograptus biozone is established for the first time in South China, increasing the late Tremadoc graptolite biozones in South China from four to five, in ascending order as follows: the Adelograptus tenellus biozone, the Aorograptus victoriae biozone, the Kiaerograptus biozone, the Sagenograptus murrayi biozone, and the Hunnegraptus copiosus biozone. A review of the occurrence records for robust Kiaerograptus species worldwide reveals that the distribution is restricted to the Aorograptus victoriae biozone and Kiaerograptus biozone in the late Tremadocian. This limited stratigraphical distribution makes Kiaerograptus a valuable taxon for precise biostratigraphical correlation at both the regional and global scales. [ABSTRACT FROM AUTHOR]

Graptolites from the early Tremadocian Anisograptus matanensis Biozone are identified from east-central Sonora, northwestern Mexico, within a carbonate-shelf succession deposited on the southwestern continental shelf margin of Laurentia. This is the second occurrence of typical anisograptid graptolites in Mexico, after its original record in the Oaxaca area, which belongs to a Gondwana-related paleogeographical realm. The graptolites from Sonora represent the second global occurrence of any member of the Rhabdinopora flabelliformis group in the Ordovician equatorial shelf region. [ABSTRACT FROM AUTHOR]

Solutans are relatively common members of echinoderm assemblages in the Saint-Chinian Formation (upper Tremadocian) of the Montagne Noire (France). The revision of all available material confirms that most specimens can be assigned to Minervaecystis vidali, which is here reconstructed for the first time. The occurrence of Plasiacystis mobilis is evidenced based on a single, well-preserved dististele. The interpretation of the small-sized individual as a putative dendrocystitid is rejected: it corresponds to a juvenile specimen of M. vidali. Early Ordovician solutans from the Montagne Noire partly fill the gap between Laurentian mid–late Cambrian syringocrinids and Avalonian-Gondwanan Early–Middle Ordovician taxa. [ABSTRACT FROM AUTHOR]

Tremadocian highly metalliferous black shales and associated grey shales from the Aseri PH012B drill core (NE Estonia) in the innermost part of the Baltic Palaeobasin were targeted to record their nitrogen and organic carbon isotope variance combined with the total organic carbon and total nitrogen record. The obtained molar C/N ratios of black shales from 26 to 52 indicate a considerable loss of N compared to primary biomass. The recorded δ15N values from –2.5 to 0.2‰ likely evolved due to isotopic fractionation related to N2 fixation by primary producers, superimposed by later anoxic ammonium oxidation processes within the uppermost sediments. The high net primary productivity, which controlled the accumulation of organic-rich shallow-water complexes, was fuelled by the internal cycling of P in the sea basin and combined with intensive N exchange between marine and atmospheric pools. [ABSTRACT FROM AUTHOR]

A Lower Tremadocian (Tr1) lingulate assemblage from the Guayoc Chico Group (Pupusa Formation) is described and illustrated for the first time. The fauna consists of poorly preserved obolids referred to Libecoviella? sp. and Torobolus cf. subplanus Benedetto & Muñoz, 2015, the acrotretid Eurytreta harringtoni Mergl & Herrera, 2015 and the siphonotretid Celdobolus skrikus sp. nov. This is the first record of the genus Celdobolus in South America, previously recorded from slightly younger strata of Bohemia and Belgium. The Tremadocian lingulate fauna from the Central Andean basin displays closest biogeographical similarity with the Bohemian and Avalonian assemblages and supports a poleward (in Ordovician coordinates) dispersal trajectory along the clastic platforms bordering the Amazonian and NW Africa cratons. On the basis of recent coupled ocean-atmosphere circulation models for the Lower Ordovician it is inferred that larvae could have been transported by the boundary cold-water Antarctica Current. [ABSTRACT FROM AUTHOR]

Ordovician marine sedimentary sequences occur in several widely separated structural blocks in Iran, along the northern margin of Gondwana. In northern Kerman Province, the Ordovician sedimentary interval is known as the Katkoyeh Formation, which encompasses ~ 70-300 m of siliciclastic rocks with scarce carbonate and thick pyroclastic beds in its upper part. Previous studies provided several ages for the Katkoyeh Formation, puzzled by the limited number of palaeontological studies, mostly based on spot samples, the presence of regional important stratigraphic gaps, and the inherent structural complexity of the area. In order to adjust the depositional time of the Katkoyeh Formation, a systematic sampling for microfossils was conducted in the Banestan Section, located about 12 km northwest of the city of Zarand, in the vicinity of the Banestan village. Based on the occurrence of important biostratigraphic species, we recorded three conodont intervals in ascending order in the Katkoyeh Formation, namely the Rossodus manitouensis/Paltodus deltifer Concurrent Range Zone (Tremadocian, Lower Ordovician), the Juanognathus variabilis Range Zone (Floian, Lower Ordovician), and the Icriodella superba Range Zone (Katian-Hirnantian, Upper Ordovician). The conodont biostratigraphy is discussed and analysed, improving the Ordovician intrabasinal correlation of Iran as well as correlation with distant palaeobiogeographic domains. The Upper Ordovician conodont assemblage is accompanied by two new species of ostracods: Satiellina zarandensis sp. nov. and Ceratopsis persicus sp. nov., both suggesting palaeobiogeographical affinities mainly with Gondwana and peri-Gondwanan regions. [ABSTRACT FROM AUTHOR]

Although phosphatized bryozoans have been described recently from the early Cambrian, the first unequivocal bryozoan fossils with hard skeletons are known from the Ordovician. Recent discoveries of bryozoans in the early Ordovician (Tremadocian) of South China have greatly expanded our understanding of the diversification of these colonial lophophorates. In particular, the Fenhsiang Formation of Late Tremadocian age (Migneintian) in Hubei Province is proving to be particularly rich in bryozoans. Here we record 24 species, including several yet to be formally described, belonging to 18 genera and four palaeostomate suborders (Esthonioporata, Cystoporata, Trepostomata, and Cryptostomata). Bryozoan diversity in the Fenhsiang Formation matches levels more typical of younger faunas of Middle Ordovician age. The presence of diverse and morphologically disparate taxa close to the base of the Ordovician suggests rapid diversification following the first appearance of bryozoans with calcified skeletons, and/or the existence of as yet unknown biomineralized bryozoans in the Cambrian. [ABSTRACT FROM AUTHOR]

An Early Ordovician fauna of linguliform brachiopods and euconodonts is described from the Alum Shale Formation in northernmost Västerbotten County, northern Sweden. The fauna was recovered from a single carbonate concretion collected at an exposure near the northern shore of Lake Storvindeln. Despite of the fragmentary and tectonized preservation of the obtained fossils, at least eight different taxa of linguliform brachiopods and four species of euconodonts could be identified. Among the brachiopods, the ephippelasmatid Pomeraniotreta biernatae Bednarczyk, 1986 is most common; it is associated among others with the acrotretids Eurytreta cf. sabrinae (Callaway, 1877) and Ottenbyella sp., and a spinose specimen potentially representing the zhanatellid Thysanotos. Two of the brachiopod taxa appear to present new species, Pomeraniotreta n. sp. and Mytoella? n. sp., but additional material would be needed for a formal description. Euconodont specimens are rare and comprise coniform elements of Drepanodus arcuatus Pander, 1856, Drepanoistodus aff. amoenus (Lindström, 1955) sensu Löfgren (1994), Paroistodus numarcuatus (Lindström, 1955) and Rossodus aff. manitouensis Repetski & Ethington, 1983. Evaluation of the stratigraphic distribution of the different taxa of brachiopods and euconodonts under consideration of the local geology, suggests that the investigated sample represents a level in the upper part of the Tremadocian (Tr2) part of the Alum Shale Formation. The fauna represents the northernmost occurrence of age diagnostic Early Ordovician (Tremadocian) fossils in Sweden. [ABSTRACT FROM AUTHOR]

A block of stromatolitic limestone found on the Angara River shore near Kodinsk, Siberia, derived from the exposed nearby Ust-kut Formation, has yielded a sample of 146 ellesmeroceratid nautiloid specimens. A minor contribution to the fossil assemblage from bellerophontid and hypseloconid molluscs suggests a restricted abnormal salinity environment. The associated shallow-water low diversity assemblage of the conodonts Laurentoscandodus triangularis and Utahconus(?) eurypterus indicates an age close to the Furongian–Tremadocian boundary. Echinoderm sclerites, trilobite carapaces, and hexactinellid sponge spicules were found in another block from the transitional strata between the Ust-kut and overlying terrigenous Iya Formation; these fossils indicate normal marine salinity. The conodont L. triangularis is there associated with Semiacontiodus iowensis and Cordylodus angulatus. This means that the stromatolitic strata with cephalopods are older than the early Tremadocian C. angulatus Zone but not older than the Furongian C. proavus Zone. The sample of nautiloid specimens extracted from the block shows an unimodal variability in respect to all recognizable aspects of their morphology. The material is probably conspecific with the poorly known Ruthenoceras elongatum from the same strata and region.

Abstract In this research, Ordovician conodonts obtained from the sedimentary succession of the informal Katkoyeh formation is studied in a stratigraphic section at the south of Kuh-e-Bonorg, eastern flank of Kalmard Anticline in the west of Tabas (Central Iran). The formation which is partly equivalent to the succession of the Shirgesht Formation in Tabas Block is unconformably overlaid the Kalmard Formation (attributed to the Neoproterozoic) and disconformably overlain by the Carboniferous Gachal formation. The Katkoyeh formation with 214.8 meter thickness is divided into three lithostratigraphic members including the Lower Sandstone (mostly quartzarenite to litharenite), Middle Shale (red to green shales interbedded with some dolomitic and calcareous sandstones, in laminated wavy stromatolite structure at the base) and Upper Carbonate (limestones, dolostones and marls). The section was sampled bed by bed for conodont studies so that 80 samples have been selected, however only seven of them were productive. Within the selected samples, six genera and 14 species of coniform and ramiform conodont elements are determined, a few of them are reporting for the first time from Iran. The obtained conodonts demonstrate the faunal assemblages equal to the proteus, elegans-evae and diprion Zones which confirm the age of Early Ordovician (late Tremadocian–Floian) for the studied section. The whole conodont material display a faunal affinity with the Baltoscandic and Argentina paleobiogeographic provinces. Keywords: Conodont, Floian, Katkoyeh formation, Ordovician, Tremadocian. Introduction In spite of the moderately -exposed outcrops of the Ordovician successions throughout the country, most of the stratigraphical studies in Iran are focused on Alborz Range (e.g.; Gansser and Huber 1962, Muller 1973, Ghavidel-Syooki 2006, Ghobadi Pour et al. 2007, 2011; Jahangir et al. 2016) and the appropriate data from the other regions are restricted to a few published reports (e.g.; Ruttner et al. 1968, Aghanabati 1977, Hamedi 1995, Ghaderi et al. 2008). Especially our knowledge is very little about the conodont contents of the Ordovician rocks in Iran. The Ordovician sedimentary succession in the north of Tabas in central Iran have been introduced as the Shirgesht Formation by Ruttner et al. (1968). The rock sequences of this formation composed of brown, cream, and green to red limestones, shales and partly sandstones with hardly more than 800 m in thickness (Ghobadi Pour et al. 2006). Lithostratigraphically, the Ordovician sedimentary interval in adjacent Kalmard Block (Aghanabati 2010) is different, includes more siliciclastic rocks somewhat carbonate beds in upper part. These succession has been considered as the Katkoyeh formation by Hamedi and Wright (1992). The less known Katkoyeh formation as an informal stratigraphic rock unit in central Iran has been regarded to Arenigian to Ashgillian in the type area in Kerman region, but the age of the formation in the Kalmard type region is dissimilar in different studies. In the current research we have looked for the succession Katkoyeh formation in a section at the south of Kuh-e-Bonorg, eastern flank of the Kalmard anticline, from the age dating view, based on the conodont contents. Material & Methods In the Kuh-e-Bonorg section, 80 rock samples were collected bed by bed for conodont content while only seven of them were productive. For this purpose, sandy limestones, dolomitic limestones and pure limestones with about 3–5 kg were dissolved by 10% formic acid and 20% acetic acid following the standard procedure for conodont extraction (e.g., Jeppsson & Anehus, 1995). Residue washed on appropriate clean 18 and 230 mesh sieve-stack (0.85 to 0.063 mm). The extracted conodont collections stored in the Ferdowsi University of Mashhad, Iran under the collection name with the FUM#MC prefix. Discussion of Results & Conclusions The Katkoyeh formation in the south of Kuh-e-Bonorg section is unconformably overlaid the Neoproterozoic rocks attributed to the Kalmard Formation and disconformably overlain by the Carboniferous Gachal formation. The Katkoyeh formation of 214.8 meter thickness in the studied area is divided into three members such as the Lower Sandstone (mostly quartzarenite to litharenite), Middle Shale (red to green shale interbedded with some dolomitic and calcareous sandstone, in laminated wavy stromatolite structure at the base) and Upper Carbonate (limestones, dolostones and marls). Among the seven fossiliferous beds, we obtained the index conodonts of Lower Ordovician which belong to six genera and 14 species of coniform and ramiform elements. The assemblage is correlative with the same collections from the Baltoscandic and Argentina paleobiogeographic provinces (e.g.; Mannik and Virra 2012; Voldman ‌‌‌‌‌‌et al. 2017). The distribution of taxa in the stratigraphic succession is variable, in abundance of elements as well as in the number of taxa. The oldest conodonts in the section, Drepanodus arcuatus and Drepanoistodus costatus, come from the dolostones and dolomitic limestones of uppermost Tremadocian-early Floian proteus Zone (equivalent to Acodus apex Zone in NW Argentina Province) the sample MC208B. The next fossiliferous bed, MC232, comprises Acodus triangularis, Acodus cf. deltatus, Drepanoistodus cf. nowlani, Drepanoistodus cf. bassiovalis, Drepanoistodus bassiovalis and Gothodus costalatus which confirm Floian elegans - evae Zones (equivalent to Gothodus vetus–Gothodus andinus Zones in NW Argentina Province). The last productive beds, MC263–MC265, contain Trapezognathus diprion as the index taxon for upper evae Zone (equivalent to Trapezognathus diprion Zone in NW Argentina Province). This species confirm the age of late Floian for the uppermost part of the Katkoyeh formation in the Kuh-e-Bonorg section.

Rare Oichnus simplex drill holes occur in mature obolid shells from the Cambrian/Ordovician boundary beds of northern Estonia (Iru and Ülgase) and the uppermost Cambrian of NW Russia (Lava River). The drill holes are significantly more common in the central rather than the marginal regions of the obolid valves. Drilling predators attacked Ungula ingrica in the Kallavere Formation and Ungula convexa in the Ladoga Formation. Failed predatory attacks on obolids were relatively common in the latest Cambrian-earliest Tremadocian of Estonia. Presumably drilling predators at Lava River and Iru differed from those at the Ülgase as indicated by significant differences in drill hole sizes at these locations. Most likely some types of worms preyed on obolids in the latest Cambrian-earliest Tremadocian of Estonia and latest Cambrian of NW Russia. The predation rate (6% to 9%) of studied obolids indicates that they likely had an epibenthic life mode. In addition to Oichnus drill holes in the obolids, there are also common pseudoborings caused by mineral dissolution. [ABSTRACT FROM AUTHOR]

Graptolites have been collected from sections through Lower Ordovician strata in northern Iran. At the Saluk Mountains, in the Kopet–Dagh region, mudrocks yielded fragmentary tubaria of Rhabdinopora sp. cf. R. flabelliformis, indicating the presence of lower Tremadocian strata there; stratigraphically, they lie between two limestone beds with the euconodont Cordylodus lindstromi. At Simeh–Kuh in the eastern Alborz Mountains (Semnan Province), upper Tremadocian – lower Floian strata include laminated dark mudstones that contain restricted graptolite faunas, mainly of small declined didymograptids; these are thought to represent incursions of plankton during periods of marine highstands. The lower major flooding surface in Simeh–Kuh coincides with an invasion of the graptolite biofacies and an incursion of Hunnegraptus? sp.; the second major flooding surface is associated with an incursion of Baltograptus geometricus. They were most probably synchronous with those in the lower part of the Hunnegraptus copiosus Biozone and at the base of the Cymatograptus protobalticus Biozone in the of the Tøyen Shale Formation succession of Västergötland, Scandinavia, suggesting that observed characters of sedimentation were eustatically controlled. [ABSTRACT FROM AUTHOR]

In the eastern Yangtze Platform of South China Block, Tremadocian (Early Ordovician) stromatolites in southern Anhui Province occur along a palaeoenvironmental transect from the shallowest intra-platform setting through to deeper platform margin. The intra-platform and platform margin belts of Tremadocian rocks in the eastern platform are carbonate-dominated marine environments favourable for calcimicrobes. However, stromatolites are absent in siliciclastic-dominated slope facies. Shallower carbonate facies are represented by the upper member of the Lunshan Formation, composed of a hundred metres thickness of stromatolite-bearing carbonates. Such stromatolites at the Beigong section of Jinxian county are characterized by stratiform and dome-shaped laminations. Girvanella filaments are ubiquitous in thin sections. Crinoids grew on the surfaces of the microbialites. In contrast, towards the deeper carbonate platform margin, stromatolites in massive-bedded limestones of the upper member of Lunshan Formation of the Ma’anshan section at Shitai occur as dense columns of bindstones; macrofossils and bioclasts are rare in those stromatolites, indicating a lower energy and deeper marine setting. Water depth at the platform margin of the Ma’anshan section is interpreted as being above the base of the euphotic zone favorable for photosynthesis in the calcimicrobial community; however, benthic fauna notably declined. In contrast to shallower settings, in clastic-dominated locations interpreted as deposited in deeper water, stromatolites are absent, represented by the middle member of Dawuqian Formation at the Ziliqian section. This work, therefore, supports that Early Ordovician reef systems were still microbial-dominated, representing the last golden age of stromatolites. [ABSTRACT FROM AUTHOR]

A small bivalve fauna is described from the late Tremadocian of Iran, adding to the very few localities in the world where bivalves of this age are known. In addition to indeterminate praenuculids, the fauna includes the praenuculid Pensarnia and the pteriomorphian genus Glyptarca. The former is otherwise known from South Wales and the latter, from South and Mid‐Wales and West Yunnan, China. [ABSTRACT FROM AUTHOR]

The recent re-interpretation of the Lower Palaeozoic euarthropod group Mollisonia as belonging to Chelicerata has triggered a renewed interest for the poorly known family Mollisoniidae. In this contribution, we revise the anatomy, taxonomic diversity, and systematics of Thelxiope, the sister-taxon of Mollisonia. This mollisoniid genus comprises four species, and is characterized by the presence of one cephalic, seven thoracic (one per tergite), and three pygidial long sagittal spines. The type species, T. palaeothalassia Simonetta & Delle Cave, is a rare taxon in the Wuliuan Burgess Shale Formation of Canada, which can be recognized by the hypertrophy of a single of its sagittal spines, the posteriomost one. T. spinosa (Conway Morris & Robison)–a species originally assigned to a distinct genus ‘Ecnomocaris’ herein synonymised with Thelxiope–is known from a single specimen found in the Drumian Wheeler Formation of the House Range of Utah. It differs from the type-species in the hypertrophy of both the anteriormost (cephalic) and the posteriormost (third pygidial) sagittal spines. The same Wheeler strata have also yielded a single specimen of a new taxon, T. holmani sp. nov., which lacks hypertrophied sagittal spines and features blunt thoracic tergopleural tips. A putative fourth species, referred to Thelxiope sp. nov. A, extends the stratigraphical range of Thelxiope to the Lower Ordovician (Tremadocian), and its palaeographic range to West Gondwana. Currently under study, this relatively common component of the lower Fezouata Shale fauna is only briefly discussed. Features characterizing the genus Thelxiope and its components almost exclusively pertain to the sagittal spines, for the scarcity and inconsistent preservation of the Cambrian materials as-yet available preclude a confident assessment of the variability of other morphological features. The pygidium in Thelxiope and Mollisonia is not composed of four, but three tergites essentially similar to thoracic ones, except for the lack of articulations. [ABSTRACT FROM AUTHOR]

Marrellomorphs (class Marrellomorpha) are a group of Paleozoic arthropods with a very poor fossil record. Here we describe a new marrellomorph arthropod Mimetaster florestaensis sp. nov. from the Tremadocian (earliest Ordovician) of Argentina. The new species is characterized by the shape and direction of the three pairs of principal spines, and the existence of strong secondary spines only in the proximal two-thirds of the anterolateral spines. As a result of phylogenetic analysis the new species integrates a trichotomy with Mimetaster hexagonalis and a Moroccan unnamed marrellid as sister groups. This discovery increases the known diversity of Marrellomorpha and represents the first occurrence of this group in South America, expanding the spatial distribution of the clade.

A block of stromatolitic limestone found on the Angara River shore near Kodinsk, Siberia, derived from the exposed nearby Ust-kut Formation, has yielded a sample of 146 ellesmeroceratid nautiloid specimens. A minor contribution to the fossil assemblage from bellerophontid and hypseloconid molluscs suggests a restricted abnormal salinity environment. The associated shallow-water low diversity assemblage of the conodonts Laurentoscandodus triangularis and Utahconus(?) eurypterus indicates an age close to the Furongian-Tremadocian boundary. Echinoderm sclerites, trilobite carapaces, and hexactinellid sponge spicules were found in another block from the transitional strata between the Ust-kut and overlying terrigenous Iya Formation; these fossils indicate normal marine salinity. The conodont L. triangularis is there associated with Semiacontiodus iowensis and Cordylodus angulatus. This means that the stromatolitic strata with cephalopods are older than the early Tremadocian C. angulatus Zone but not older than the Furongian C. proavus Zone. The sample of nautiloid specimens extracted from the block shows an unimodal variability in respect to all recognizable aspects of their morphology. The material is probably conspecific with the poorly known Ruthenoceras elongatum from the same strata and region. [ABSTRACT FROM AUTHOR]

The Middle Shale Member of the Amdeh Formation is interpreted to be of Early Ordovician age based on its trace fossils, stratigraphic context and a newly discovered fauna of conodonts. The member abruptly overlies the Lower Quartzite Member, which may be Early Cambrian, and passes gradationally-upward into the Upper Quartzite Member, which is probably Early–Middle Ordovician. The 542.5 m thick Middle Shale Member can be divided into two parts: a shaly lower part, and a sandy upper part that contains an influx of heavy minerals. Bioturbation by marine trace fossils is one of the most obvious characteristics of the member. The shales and sandstones are interpreted to be of Cruziana and Skolithos ichnofacies and represent shallow-marine shelf, shoreface, beach and coastal deposits. Sparse shelly fossils occur in the sandy upper part, principally bivalves, inarticulate brachiopods, ostracods and conodonts. The small assemblage of conodonts includes elements interpreted to be Tremadocian (Tetraprioniodus , Drepanoistodus , Drepanodus , Scolopodus , ? Tropodus , Semiacontiodus and Teridontus), and others which may be Floian or ancestral forms of Floian taxa (Balognathidae gen. et sp. indet. A & B and aff. Erraticodon). No acritarchs have been recovered, probably due to high temperatures experienced during burial to >6 km. It is likely that the Middle Shale Member is the seaward equivalent of the Mabrouk and Barakat formations, and an outcrop gamma-ray log supports such a correlation. The trace fossils, sedimentology, conodont fauna and the general lack of macrofossils are in keeping with the regional Tremadocian–Floian of the Arabian margin of Gondwana. [ABSTRACT FROM AUTHOR]

Chitinozoans are a group of biostratigraphically valuable microfossils which appeared in the Tremadocian and diversified during the rest of the Great Ordovician Biodiversification Event, to become extinct in the Devonian. The early diversification of chitinozoans on the Baltica palaeocontinent has remained poorly known due to preservation and collecting bias. In this study we document the distribution of chitinozoans through the upper Tremadocian to lower Darriwilian strata in the Jägala waterfall section from northern Estonia, in order to better understand the regional diversity patterns and biogeographic links. Fifty samples were studied from the 7.5 m succession of sandstones, marls and carbonates revealing 47 chitinozoan species and 11 genera. The lowermost productive samples, attributed to the late Tremadocian, represent the earliest rich chitinozoan fauna from Baltica. Combined with previous reports this shows a diversity peak in the Tremadocian with balanced total diversity reaching 17, possibly followed by a decline in the Floian and then a rather gradual increase through the Dapingian and early Darriwilian. The new diversity curve shows more than three times higher values for the Tremadocian and Dapingian than indicated in previous studies, and thus less abrupt radiation in the Darriwilian. The Jägala section provided also new data on the regional biozonal species Conochitina cucumis and Cyathochitina regnelli , which characterize the middle and upper Volkhov and lower Kunda regional stages, respectively. Several other biostratigraphically significant taxa typical of other regions were recovered from the Jägala section, including Conochitina decipiens and Desmochitina bulla. A new short-ranging species Laufeldochitina toilaensis sp. nov. is introduced, having potential to become an index species for middle Dapingian strata. The early Darriwilian assemblage from Jägala includes Rhabdochitina sp. A with up to 2.7 mm long vesicle, making it the largest chitinozoan ever reported. • Rich assemblage of Early and Middle Ordovician chitinozoans recovered from Baltica. • A peak in regional diversity of chitinozoans occurred in the late Tremadocian. • The main phase of GOBE was more gradual on Baltica than previously known. • The largest chitinozoan with 2.7 mm long vesicle recovered from the Darriwilian. [ABSTRACT FROM AUTHOR]

Abstract The extinct echinoderm clade Stylophora consists of some of the strangest known deuterostomes. Stylophorans are known from complete, fully articulated skeletal remains from the middle Cambrian to the Pennsylvanian, but remain difficult to interpret. Their bizarre morphology, with a single appendage extending from a main body, has spawned vigorous debate over the phylogenetic significance of stylophorans, which were long considered modified but bona fide echinoderms with a feeding appendage. More recent interpretation of this appendage as a posterior "tail-like" structure has literally turned the animal back to front, leading to consideration of stylophorans as ancestral chordates, or as hemichordate-like, early echinoderms. Until now, the data feeding the debate have been restricted to evaluations of skeletal anatomy. Here, we apply novel elemental mapping technologies to describe, for the first time, soft tissue traces in stylophorans in conjunction with skeletal molds. The single stylophoran appendage contains a longitudinal canal with perpendicular, elongate extensions projecting beyond hinged biserial plates. This pattern of soft tissues compares most favorably with the hydrocoel, including a water vascular canal and tube feet found in all typical echinoderms. Presence of both calcite stereom and now, an apparent water vascular system, supports echinoderm and not hemichordate-like affinities. [ABSTRACT FROM AUTHOR]

The eoorthid brachiopod Apheoorthina is reported for the first time from the Lower Ordovician of NW Argentina. It is represented by a species similar to A. ferrigena from the Tremadocian of the Prague Basin, increasing the faunal affinities between the Central Andean Basin and the South European microcontinents, in particular the Bohemian region (Perunica). Nine out of the fourteen brachiopod genera reported from the Tremadocian of the Central Andean Basin (~64%) are shared with the Mediterranean region, four of which (~28%) have been recorded in the Prague Basin, and two (Kvania and Apheoorthina) are restricted to the Central Andes and Perunica. Dispersal pathways around Gondwana are analyzed in the light of major factors affecting large-scale distribution of brachiopods (environment, larval capacity for dispersal, oceanic currents). The presence in Apheoorthina aff. ferrigena of a well-preserved larval protegulum measuring 420 μm in width and 210 μm in length strongly suggests that this species had planktotrophic larvae capable of long-distance dispersal. According to recent ocean-atmosphere general circulation models for the Ordovician Period, the Central Andean margin was dominated by the cold-water Antarctica Current. Despite the complex non-zonal pattern produced by current deflections around the peri-Gondwanan microcontinents, the general westward circulation sense favoured larval dispersal from the Andean region to North Africa, Avalonia, the Armorican Terrane Assemblage, and Perunica. On the other hand, the eastwards flowing Gondwana Current connected the North Gondwana waters with the South American epicontinental seas, which could explain the reversed migration of some brachiopods.

The transition from the Cambrian to Ordovician in Morocco is known to be characterized by a frequent Furongian hiatus, restricted extension of the Tremadocian marine deposits, and frequent unconformities at the base of the transgressive upper Floian deposits. In the present work, we first highlight the occurrence of Fe- and mica-rich, red silty/sandy formations in the Central and Eastern High Atlas between the Middle Cambrian and Upper Floian sequences. In the Tislyt type-locality, a synsedimentary hemigraben structure is defined, within which the red beds show frequent slump folds, debris flows and internal unconformities. The correlation with several coeval series of the Meseta domain allows us to define a shallow marine, ferruginous clastic Atlas-Meseta Red Beds (AMRB) basin during the Tremadocian-early Floian. The AMRB basin extended between the Meseta coastal block and the Anti-Atlas domain, being limited by the fault zones that became the West Meseta shear zone and the South Meseta fault, respectively, in the Variscan orogen. The AMRB basin compares with the coeval rifted basins of the central Iberian and Armorican massifs. The red beds were likely sourced from the east, from both the Precambrian basement and Early Ordovician magmatic rocks, contrary to the Ordovician deposits of the Sahara platform sourced from the south. Subsidence of the AMRB and central Iberian-Armorican basins of the NW-Gondwana border aborted during the Floian, whereas the opening of the Rheic ocean went on more to the west.

Restudy of the Cambrian–Ordovician boundary beds, traditionally assigned to the Mila Formation Member 5 in Mila-Kuh, northern Iran, for the first time provides convincing evidence of the Early Ordovician (Tremadocian) age of the uppermost part of the Mila Formation. Two succeeding trilobite assemblages typifying the Asaphellus inflatus–Dactylocephalus and Psilocephalina lubrica associations have been recognized in the uppermost part of the unit. The Tremadocian trilobite fauna of Mila-Kuh shows close similarity to contemporaneous trilobite faunas of South China down to the species level, while affinity to the Tremadocian fauna of Central Iran is low. The trilobite species Dactylocephalus levificatus and brachiopod species Tritoechia tenuis from the Tremadocian of Mila-Kuh are new to science.

The lower Palaeozoic marine succession of NE Vietnam accumulated on the South China plate. Despite historical works dating to French colonial times, the stratigraphy and palaeontology of the succession is poorly constrained. Chief amongst the lower Palaeozoic lithostratigraphical divisions is the Than Sa Formation, a c. 1200 m thick succession of clastic rocks of Cambrian and early Ordovician age. Newly collected graptolites (including Rhabdinopora ? sp. and Tetragraptus approximatus) from the upper part of the formation identify strata assignable to the Tremadocian and Floian stages of the Lower Ordovician. The same succession also probably records the Cambrian–Ordovician boundary. Our analysis identifies one or more intervals of graptolite-bearing laminated mudstones in the upper part of the Than Sa Formation that may be widespread in NE Vietnam during the early Tremadocian. [ABSTRACT FROM AUTHOR]

First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long‐distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity. [ABSTRACT FROM AUTHOR]

Morphometrics can be an important tool in systematic studies, providing taxonomists with strong elements of quantification and formal hypothesis testing. Here, these tools are tested for the trilobiteLeptoplastides marianus(Hoek) which was originally described on the basis of three deformed specimens from west Tarija, Bolivia. Following the conclusions of Harrington & Leanza, a wide range of morphological variation is accepted for this species, and the name was applied to a large number of specimens from north-western Argentina. Based on specimens collected from the quebrada Moya (Huacalera, Jujuy), as well as on material in the Harrington & Leanza collections in the University of Buenos Aires, traditional morphometric and geometric morphometric methods were used to evaluate the variation of the cranidial shape ofL. marianussensu Harrington & Leanza. The results allow discrimination between two clearly different morphotypes. The nameL. marianusshould be restricted to the type specimens, given the deformation of these materials. In addition,L. argentinensisandL. granulosusare both valid names for the two morphotypes recognized in the present paper. [ABSTRACT FROM PUBLISHER]

The high-resolution study of vertical geochemical variability of shallow-water Tremadocian black shales of the Türisalu Formation targeted two drill core sections from Suur-Pakri Island, NW Estonia. Altogether 374 samples from 4.6 m thick shale were analysed by XRF. The metalliferous and organic-rich black shales revealed significant centimetre-scale variation in the concentration of redox-sensitive trace metals – U, Mo and V. The V profiles show cyclic variations in half a metre- to metre-scale and the strongest correlation with loss on ignition (LOI) 500 °C (interpreted to reflect organic matter abundance). The abundance of Mo presents high values near the lower and upper contacts of black shale and otherwise moderate covariance with LOI. The distribution of U is not coupled with LOI, being characterized by irregular local enrichment anomalies in the profiles of both sections. This suggests that sequestration of U may have been time-dependent and possibly favoured by dissimilatory U-reduction at the sediment–water interface under iron-reducing conditions. Significant depositional variability of the studied organic-rich muds apparently supported dynamic physicochemical and biological microenvironments at the sediment–water interface and thus temporally and spatially diversified the paths and efficiency of synsedimentary redox-sensitive trace element enrichment.