TELYCHIAN (LLANDOVERY, SILURIAN) BIVALVES FROM SPAIN

Abstract:  Twenty species of bivalves (14 new) and 14 genera (six new) are described from two localities in the Silurian, upper Telychian, Oktavites spiralis Biozone of Spain: Cardavia cathleenae gen. et sp. nov., C. hafi sp. nov . , C. stefani sp. nov.; Copenychia franta gen. et sp. nov., C. pristina sp. nov.; Stolidotus marco sp. nov.; Telycardia malinka gen. et sp. nov.; Silurinka vetula gen. et sp. nov.; Bolsopteria lentilka gen. et sp. nov.; Nennapteria ibericola gen. et sp. nov., N. ollicula sp. nov.; Actinopteria dakryodes sp. nov., A. isabelae sp. nov. and Dceruska hispanica sp. nov. They comprise two closely related communities, the Copenychia-Cardavia-Actinopteria Community and the Dceruska-Copenychia-Stolidotus Community, which belong to the Snoopyia Community Group. The occurrence of Dceruska Barrande, 1881, Dualina Barrande, 1881, Patrocardia Barrande, 1881, Silurinka , gen. nov., Slava Barrande, 1881 and Stolidotus Hede, 1915 in the Telychian of the Central Iberian Domain, Spain, supports palaeogeographical relationships with other Lower Silurian regions of north Gondwanan and Perunican Europe: the Carnic Alps (Austria), the Montagne Noire (France), Sardinia (Italy) and the Prague Basin (Bohemia), and also to Avalonia: the Welsh Borderland (Great Britain) and Baltica–Skåne (Sweden). These genera together with the new genera Cardavia, Copenychia (the earliest known representatives of the Silurian family Cardiolidae), Telycardia (the oldest known representative of the family Praecardiidae) and Silurinka belong to a Bohemian type of bivalve. Bolsopteria lentilka is closely related to Bolsopteria elliptica (Hind, 1910) from the Aeronian (middle Llandovery) of Scotland.     

Cardiolinka bohemica (Barrande, 1881) – A first representative of the Late Silurian Bohemian type Bivalvia fauna from the northern Arabian Plate,Southeast Turkey

The Rheic Ocean was a major oceanic domain between Baltica, Laurentia, Perunica and Gondwana in Ordovician-Silurian times. The cosmopolitan nepiomorphian bivalves Praecardioidei Newell, 1965 and Antipleuroidei Kříž, 2007 are characteristic of the Silurian of Perunica, peri-Gondwana, and Baltica, and occur also in Laurentia and Siberia. The Bohemian-type bivalve Cardiolinka Kříž, 1981 (Nepiomorphia Kříž, 2007, Cardiolidae Hoernes, 1884), from the Late Silurian of the Bahar-1 well core, has been found for the first time in southeastern Turkey. The strata containing the species Cardiolinka bohemica (Barrande, 1881) occur in the middle part of the Dadaş Formation in the interior Petroleum District X-Siirt of the northern parts of the Arabian Plate. The cosmopolitan species C. bohemica was until now known from the Latest Ludlow to Pridoli of the Prague Basin, France, Carnic Alps, Sardinia, East European Platform (Poland), eastern Serbia, Moesian Platform, and Arctic Canada. The new surprising subsurface data on C. bohemica in Diyarbakır-Bismil area (southeastern Turkey) therefore represent another piece of evidence in favour of strong faunistic affinity between Perunica, peri-Gondwanan Europe and the northern Gondwana margin.     

Biological and stratigraphical significance of the Silurian nautiloid Aptychopsis

Turek, Vojtach 1978 04 15: Biological and stratigraphical significance of the Silurian nautiloid
Circular or elliptical structures described as the genus Aptychopsis Barrande 1872 (and mostly referred to the Crustacea) represent the opercula of a specialized group of orthoceratids. Their morphology bears a considerable resemblance to the structure of the lower jaws (aptychi) of some Mesozoic ammonoids, particularly of the genus Physodoceras . Because of its size and structure, however, Aptychopsis cannot have functioned as a jaw apparatus. Observation of an operculumin siru supports this assumption as regards its functional and systematic position. The classification of the genus Aptychopsis as given by Jones and Woodward (1872–1893) is purely typological and hardly applicable in palaeobiology. Continuous gradations exist between the various morphological types. The lack of systematically distinctive features explains the unsuitability of Aptychopsis for biostratigraphical use. Aptychopsids occur in the Silurian of Central Bohemia between the Spirograprus turriculatus Zone and the Neodiversograptus nilssoni Zone, inclusive, with maximum frequency in the uppermost Wenlockian.     

ORIGIN, EVOLUTION AND CLASSIFICATION OF THE NEW SUPERORDER NEPIOMORPHIA (MOLLUSCA, BIVALVIA, LOWER PALAEOZOIC)

Abstract: A number of bivalve taxa defined in the past as ‘Cryptodonten’ by Neumayr, 1884 were grouped together in the high‐level taxon Palaeoconchae Neumayr, 1884. Cox (1969) noted that Palaeoconchae and Cryptodonta were synonymous and Newell (1969) used Cryptodonta as a subclass of bivalves. However, for the past 120 years, the Cryptodonta has been poorly conceptualized and the name was used for poorly understood genera or those lacking dentition. As used by Newell, Cryptodonta included taxa now placed in the subclasses Protobranchia Pelseneer and Autolamellibranchiata Grobben, and to the class Rostroconchia Pojeta, Runnegar, Morris and Newell. The bulk of Newell's use of Cryptodonta was made up of Silurian and Devonian taxa first described by Barrande (1881) from Bohemia; Newell placed these in the order Praecardioida Newell. In effect, Cryptodonta became a ‘wastebasket’ grouping for what, at the time, were poorly understood taxa. Many of the formerly poorly understood praecardioids are now better known and are herein placed in the new superorder Nepiomorphia. The Nepiomorphia contains two orders: (1) order Praecardioida that includes the families Slavidae K?í?, Cardiolidae Hoernes, Praecardiidae Hoernes and Buchiolidae Grimm; and (2) new order Antipleuroida that includes the families Stolidotidae fam. nov., Spanilidae fam. nov. and Antipleuridae Neumayr. The Nepiomorphia originated probably in the early Silurian as result of r‐selection progenesis. When the marine current system became re‐established after the late Ordovician glaciation and in the early Silurian, an at least temporary ventilation of the shallow waters by surface currents was renewed in higher latitudes of peri‐Gondwana and Siberia, producing acceptable sea‐bottom environments. Larvae were distributed by surface currents from the warm tropical regions of Laurentia and Baltica and were among the first benthic organisms to colonize the new environments. Temporary ventilation created frequent density‐independent catastrophic mortalities of early ontogenetic stages, with no competitors and with super‐abundant resources. During the Silurian and early Devonian, the Nepiomorphia underwent several diversifications in the recurring cephalopod limestone biofacies characteristic of peri‐Gondwana, and evolved infaunal, semi‐infaunal and epifaunal modes of life in several lineages. The Nepiomorphia most probably became extinct during the early Carboniferous and had no role in the future evolution of the Bivalvia.     

Ecological aspects of a silicified bivalve fauna from the Silurian of Gotland

The silicified Wenlockian (Silurian) bivalve fauna from MÖllbos, Gotland, is part of a life assemblage. The vast number of shells show unusual phenomena, e.g. shell repair, pearl and tumour formation, etc. A number of shells contain epibionts and bored, round holes. Presumptive predators of the bivalve community are discussed. Size-frequency distribution of the two most abundant species possibly reflects age classes. The fauna, comprising eleven species, is dominated by deposit-feeders (90 %). They exhibit niche diversification, including at least three different feeding levels within the sediment.     

新疆巴里坤三塘湖志留纪三叶虫

新疆巴里坤三塘湖晚志留世阿苏山组三叶虫包括Ananaspis fecunda Barrande,Cheirurus barkolensis sp.nov.和Pacificurus sp.,与准噶尔盆地西北部乌图布拉格,哈萨克斯坦及捷克波西米亚的晚志留世三叶虫关系密切。另外对中国5个地区晚志留世三叶虫地层作了对比。Ananaspis,Pacificurus二属在中国是初次发现。     

Evolution within the Silurian cephalopod genusInversoceras

Specimens of the Silurian cephalopod genusInversoceras from the Wenlockian Slite Beds of Gotland, Sweden, are more curved and swollen than those from the Ludlowian Hemse Beds of Gotland. The former population is interpreted as a direct ancestor to the latter. The younger form,Inversoceras p. perversum, originally described by Barrande from Bohemia, includes both individuals with a fairly straight shell and with a slightly curved shell. The distinctly curved and swollen form from the Wenlock beds is herein described as a new subspecies,I. p. eoperversum. I. p. falciformis from the Ludlowian of Bohemia is excluded fromI. perversum and. treated as a distinct species. Its relationship to the olderI. p. eoperversum is discussed. This discussion also includesI. dayi from the Niagarian of North America.     

Reassignment of Pentamerus davyi Oehlert to Zdimir robustus (Barrande) (Brachiopoda,Devonian): Stratigraphic and palaeogeographic implications

The brachiopod fauna of the Chalonnes Limestone (Armorican Massif, France) is famous because of the presence of large, thick-shelled species first described by Oehlert (1881). One of these species originally assigned to Pentamerus davyi Oehlert, 1881 is here revised. External as well as internal characters of the shell allow its attribution to Zdimir robustus (Barrande, 1879), a species from the Trebotov Limestone in the Prague area. This reassignment is consistent with an Upper Emsian age for the Chalonnes Limestone.     

An Alpine immigrant: Phragmoceras Broderip, 1839 from the Silurian of the Carnic Alps (Austria)

A rare occurrence of Phragmoceras imbricatum Barrande is recorded from moderately shallow marine Silurian sequences in the Carnic Alps (Austria). The specimen was collected from a condensed series of nautiloid-bearing wackestones/packstones which are documented as being one of the earliest levels of the Silurian Cephalopod Limestone Biofacies deposited along the North Gondwana margin. The presence of this genus and particular species in the Alpine area, whether as an in situ fauna or as a “stray immigrant”, during a period of global eustatic lowstand, adds new data with regard to the mechanisms of faunal exchange of nectobenthic nautiloid taxa between the Carnic Alps, the Prague Basin, SW Sardinia, Avalonia and Baltica which must have been made possible by currents connecting all five areas. It seems likely that some of the nautiloid taxa appearing in the Prague Basin during the Ludlow may have already been present in the Carnic Alps much earlier in the Silurian; these document early faunal affinities with Baltica. As well as confirming the existence of open migrational seaways between these terranes at a precise stratigraphic interval during the Silurian (lower Homerian: Wenlock), the presence of this species also indicates a prevailing more temperate paleoenvironment in these areas which this element of a usually tropical fauna could tolerate, and provides significant evidence that warm water currents reached the Carnic Alps at this time. In addition due to the bathymetric restrictions of the shells of these particular faunas, exchange by currents could not have taken place over great distances, even considering drifted individuals, and therefore indicates the relatively close positions/connections of various peri-Gondwana Terranes such as the Carnic Alps, SW Sardinia and the Prague Basin to Avalonia and Baltica during this time slice.     

Two micromorphic bivalves from the Silurian of Gotland

Two new micromorphic bivalve species from the Silurian of Gotland are described and assigned to the new genusKenzieana, viz.Kenzieana lata andKenzieana angusta. Kenzieana exhibits morphological features characteristic of some unrelated extant species; above all a conspicuous antero-posterior flattening of the shell. Probably it was a siphonate suspension feeder with a reclining mode of life.     

Growth and variation in the Silurian proetide trilobite Aulacopleura konincki and its implications for trilobite palaeobiology

Morphometric analysis of growth in Aulacopleura konincki reveals several important features: (1) morphological variability is approximately constant throughout growth, increasing slightly in later ontogeny; (2) shape is more tightly constrained than the numbers of postcephalic segments, which can be quite variable; and (3) a major ontogenetic transition occurs at glabellar lengths of about 1.7 mm. This transition divides the ontogeny into two distinct growth phases, is smooth rather than abrupt, and is expressed as changes in growth trajectories, especially in the pygidium. The transition is not strictly correlated with the number of thoracic or pygidial segments. These results suggest a re-evaluation of the concepts of meraspid and holaspid growth stages in A. konincki , using growth trajectories rather than thoracic segment number to define the stages. Developmental flexibility in holaspid segment numbers in this phylogenetically advanced trilobite suggests that environmental factors, rather than phylogenetic constraint, may explain variations in segment production patterns within some advanced Trilobita. Morphometrics, trilobites, ontogeny, variability, segmentation, Silurian, Czech Republic.     

Dissepiments in the graptolite Monograptus turriculatus

An example of the graptolite Monograptus turriculatus (Barrande, 1850) from the crispus Biozone (Silurian, Llandovery) of the Girvan district, Scotland, shows the first recorded instance of dissepiment formation in graptoloid graptolites. The dissepiments are formed by the fusion of thecal spines with the dorsal wall of the adjacent part of the succeeding whorl of this spiral graptolite. The formation of these structures appears easiest to envisage using models of the graptolite colony that do not involve extrathecal tissue. □ Graptolithina , Monograptus, morphology, functional morphology, Silurian, Llandovery.     

Aspects of crinoid palaeontology of the North Esk Inlier,Scotland (Silurian,Llandovery, Telychian)

Abstract: The described fauna of well‐preserved Llandovery (Telychian) echinoderms from the North Esk Inlier, including six crinoids, one echinoid and seven starfish species, is mainly allochthonous. Most of these taxa are known only from starfish beds, channel fill deposits probably representing submarine mass flows and preserving a biota probably derived from elsewhere, presumably shallower water. Only one crinoid species, Pisocrinus cf. campana Miller, is recognized as a common fossil away from the starfish beds and is a biostratigraphic marker for the base of the Wether Law Linn Formation, forming part of the Skenidioides‐Cyrtia Association. Crinoid columnals preserved perpendicular to bedding (that is, in putative life position) in Lamont’s bivalve bed, Deerhope Formation, are tentatively interpreted as being in situ by comparison with a similar occurrence in the Silurian of Arisaig, Nova Scotia. Two new species of crinoid are described, the cladid Dendrocrinus? sp. and the columnal morphospecies Pentagonocyclicus (col.) lamonti sp. nov.     

A soft-bodied lophophorate from the Silurian of England

Soft-bodied taxa comprise an important component of the extant lophophorate fauna, but convincing fossils of soft-bodied lophophorates are extremely rare. A small fossil lophophorate, attached to a brachiopod dorsal valve, is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of England. This unmineralized organism was bilaterally symmetrical and comprised a subconical body attached basally to the host and partially enclosed by a broad ‘hood’; the body bore a small, coiled lophophore. Where the hood attached laterally, there is a series of transverse ridges and furrows. The affinities of this organism probably lie with Brachiopoda; the hood is interpreted as the homologue of a dorsal valve/mantle lobe, and the attachment as the homologue of the ventral valve and/or pedicle. The ridges are arranged in a manner that suggests constructional serial repetition, indicating that they are unlikely to represent mantle canals. Extant brachiopods are not serially structured, but morphological and molecular evidence suggests that their ancestors were. The new organism may belong to the brachiopod stem group, and might also represent a significant element of the Palaeozoic lophophorate fauna.     

Silurian craniide brachiopods from Gotland

Seven craniide brachiopod genera are described from the Silurian (Wenlock–Ludlow) of Gotland, including one new genus and five new species. The new genus and species Thulecrania septicostata is unique among Silurian craniides as it possesses solid spines. The new species Lepidocrania multilamellosa is the first Silurian record of this poorly known Permian genus. The problematic North American Propatella Grubbs, 1939 , was originally described as a gastropod, but the new species Propatella palmaria from Gotland shows that it is a craniide with sutured hollow spines of a type not previously recorded from Silurian craniides. The dorsal valves of the new species Valdiviathyris? bicornis are remarkably similar to those of the type species and represent the first possible Palaeozoic record of this poorly known extant craniide. This first systematic study of craniide brachiopods from the Silurian of Gotland shows that the diversity is relatively high as compared to other known Silurian craniide faunas, but a more thorough comparison is not possible due to the lack of data from most parts of the world. The new data from Gotland support the view that the craniides were not affected by the end‐Ordovician extinction.     

Utility and precision of Silurian graptolite biozones

The various past uses of the assemblage-zone and biozone concepts are reviewed and a modern definition of biozone is given. Silurian biozones are related to the recentideas on standard reference (graptolite) zones (SRZs) and primary biozones (PBs). Use of evolving lineages, interregna, numerical notation systems, and chronozones are discussed. Precision in correlation of the Silurian biozones is described in terms of the Ordovician-Silurian boundary and the Wenlock-Ludlow (Silurian) boundary. A number of recommendations are made with respect to all zonal concepts, essentially giving prime importance to the use of biozones. □ Biozones, standard reference zones, primary biozones, chronozones, graptolites.     

Late Silurian trilete spores from northern Jiangsu, China

The Late Silurian is generally considered to a particular significant key period in the study of early land vascular plants. A trilete spore assemblage of the Upper Silurian is described from northern Jiangsu, China. This assemblage comprises 11 genera and 20 species of trilete spores (including laevigate, apiculate, perinotrilite, patinate, rarely distally murornate and equatorially crassitate, and three indeterminate trilete miospores forms). It has similarities to those described from coeval assemblages from around the world (e.g., England and South Wales; Tripolitania, Libya; Cornwallis Island, Canadian Arctic; Northwest Spain). The rare cryptospore, only one specimen (Tetrahedraletes sp.) had been found to be associated with the Chinese trilete spore assemblage. The discovery of the trilete spores from Late Silurian rocks indicates the existence of early land plants, some possibly vascular, at that time in northern Jiangsu, China.     

Late Silurian brachiopods from Darhan Mumingan Joint Banner, Inner Mongolia

Seven brachiopod species (including three new species) and three undetermined forms are described and figured here from an unnamed stratigraphic unit which mainly consists of argillaceous and bioclastic limestone near the stratotype of the Late Silurian Xibiehe Formation of the Xibiehe section in the Darhan Mumingan Joint Banner, north of the Bateaobao area, Inner Mongolia. Three new species, Eoschizophoria minuta, Navispira navicula and Howellella asiatica are established with transverse serial sections for their interiors. All brachiopod taxa described here show that this unnamed stratigraphic unit is higher than the Late Silurian Xibiehe Formation in the Xibiehe section and is possibly transitional between the Late Silurian and the Early Devonian. Authors temporarily regard this unit as the upper part of the Xibiehe Formation in this paper.     

Pattern of some Silurian bioevents

The best‐known Silurian bioevent occurred at the end of the Wenlock: the lundgreni event, together with the nassa‐ludensis crisis, was established among planktic graptolites. The East Baltic data show several peaks of high diversity (especially triangulatus, turriculatus, scanicus zones) and three levels of low diversity of graptolites (antennularius, radians, ludensis zones). These are more or less coincident with sea‐level changes. Energetic innovation of the shallow shelf corals started in the early Silurian. The late Wenlock regression seems not to affect them seriously but the late Silurian decline coincides with the aridization of the climate and a regression of the shelf seas. The Agnatha had strong radiations in the Wenlock (ludensis Zone) and Ludlow (leintwardinensis Zone), the fishes in the Pridoli. Many Silurian vertebrates were long‐ranging and extinction rate was relatively low; only at the late leintwardinensis level and in the latest Ludlow did considerable extinctions occur.