Llandoverian and Wenlockian Cyrtograptus,and some other Wenlockian graptolites from Northern and Arctic Canada

Llandoverian and Wenlockian graptolite zonesin northern and Arctic Canada comprise the Sakmaricus-Laqueus Zone of latest Llandoverian age, Centrifugus Zone of earliest Wenlockian age, Rigidus Zone of about mid-Wenlockian age, possibly the Perneri Zone of late Wenlockian age, and the Testis-Lundgreni Zone of very late Wenlockian age.Species of Cyrtograptus described and illustratedin this study are C. centrifugus, C. cf. insectus, C. aff. lapworthi, C. laqueus, C. lundgreni, C. sp. (aff. C. lundgreni), C. mancki, C. radians, C. rigidus, C. sakmaricus, C. solaris n. subsp.? and C. sp. (similar to C. murchisoni bohemicus). Other taxa comprise Monograptus cf. capillaceus, M.? aff. deubeli, Gothograptus nassa, Plectograptus praemacilentus, Spinograptus cf. spinosus and Retiolites nevadensis.     

Stratigraphical setting of the Silurian thelodonts from Prince of Wales Island, Northwest Territories

Additional and corrected information is given regarding the stratigraphy and palaeoecology of the thelodont-bearing sequence on Prince of Wales Island. The thelodont fauna is not older than latest Wenlockian.     

Silurian (Wenlock–ludlow) Graptolites from Bolivia

Well preserved middle to upper Silurian (Wenlock–Ludlow) graptolites from Bolivia are described for the first time. Generally monospecific graptolite faunas, of species largely endemic to South America, are found in a few levels in the lower part of the Kirusillas, Rio Carrasco and Uncía formations. The oldest identified level yields specimens of Pristiograptus praedeubeli (Jaeger) and is referred to the upper Wenlock. Younger faunas belong to the Ludlow and include Saetograptus , Monograptus and Neodiversograptus specimens. These may be referred to the Gorstian (lower Ludlow). The fauna includes Saetograptus argentinus robustus ssp. nov. and Monograptus bolivianus sp. nov.     

Silurian Leptaeninae (Brachiopoda) from Gotland, Sweden

Strophomenid brachiopods belonging to the generaLeptaena andLepidoleptaena are described from the uppermost Llandovery — Ludlow succession of Gotland, Sweden. In Gotland,Lepidoleptaena comprises the single speciesL. poulseni, andLeptaena includes four species:L. rhomboidalis, L. sperion, L. depressa andL. parvirugata n. sp.L. depressa shows a considerable amount of morphological variation, which is recognised in the two new subspeciesLeptaena depressa visbyensis n. ssp. from the Llandoverian — Wenlockian Visby Formation, andL. depressa lata n. ssp. from the mid-Wenlockian Slite Group. The distribution of the different species is largely substrate-dependent, withLeptaena rhomboidalis andLepidoleptaena poulseni adapted to high-energy environments with firm substrates, whereas the remaining species preferred fine-grained substrates in low-energy environments.      

THE ZONES OF MONOGRAPTUS HERCYNICUS AND MONOGRAPTUS FALCARIUS IN PAI-KHOI

In the continuous, tectonically undisturbed section of the Upper Silurian-Lower Devonian carbonatic-terrigenous deposits on the Kara Sea shore, north-western Pai-Khoi, there occurs a succession of graptolite zones, i.e. those of Pristiograptus transgrediens, Monograptus uniformis s.l., and Monograptus hercynicus , with Monograptus praehercynicus at the base. The upper boundary of the Monograptus hercynicus zone is established by the appearance of Monograptus falcarius Koren', M. aequabilis notoaequabilis Jaeger (= M. aequabilis amdermaensis Koren'), and M. aff. thomasi Jaeger in beds just overlying shales with the youngest: records of M. hercynicus. These beds are to be recognized as the new Monograptus falcarius zone, the extent of which corresponds to the vertical range of the zonal species in the section studied. The Monograptus falcarius zone is considered to be older than the Monograptus yukonensis zone and fills the gap in the graptolite sequence in the lower part of the Pragian.     

Early Ludlow monograptids with Devonian morphological affinities

Nilssoni–scanicus Zone deposits (Silurian, early Ludlow) from the Leintwardine and Long Mountain districts of Britain, and the Clrasi Borehole, Moesian Platform of Romania, have yielded a species of monograptid which, whilst resembling rare Ludlow Monoclimacis species, has strong morphological affinities with Devonian monograptids such as Monograptus ramstalensis Jaeger. Because of the occurrence of such structures at a surprisingly low horizon the writers urge caution in identifying age from monotypic assemblages. The difficulties surrounding the affinities of the low Ludlow species necessitates a provisional open nomenclature as Monograptus sp. The possible evolutionary significance is discussed.     

Devonian features in Ludlovian graptolites — no guide to ancestry

A diverse group of Ludlovian Monograptus species is characterized by the retarded growth of thecal hoods, either proximally [ M. colonus (Barrande), M. chimaera (Barrande) and M. haupti Kühne] or throughout the rhabdosome [M. micropoma (Jaekel)]. In all these species the hoods are secondary structures, i.e. later growth additions to the thecae. By contrast, in the Devonian Monograptus species the thecal hoods are primary structures, i.e. the outward extension of the dorsal thecal wall. and are formed by undelayed growth that typically is completed before growth of the succeeding theca begins. It is among Ludlovian ( M. uncinatus Tullberg) and Pridolian ( M. simih Přibyl) forms with homologous hoods that the roots of the majority of the Devonian Monograptus species might be found. The Ludlovian M. micropoma and M. haupti should not be affiliated to the group of Monograptus vomerinus (Nicholson), which is highly characteristic of, and restricted to, the late Llandovery and Wenlock graptolite faunas.     

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.     

REMARKS ON THE STRATIGRAPHY AND MORPHOLOGY OF PRAGUIAN AND PROBABLY YOUNGER MONOGRAPTIDS

Praguian and probably younger graptoloids as well as the early Lower Devonian (Lochkovian) graptoloids are known from all continents except Antarctica and South America. At least five to six graptolite zones can now be distinguished in the Lower Devonian. In comparison with the Lochkovian faunas, the medial to late Lower Devonian graptoloid communities are considerably impoverished and composed exclusively of Monograptus species of the M. uncinatus group. Lino-graptus and Abiesgraptus , which are characteristic of much of the Lochkovian, are lacking in Praguian (and younger) strata. Monograptus pacificus from the southeast Alaskan Karheen Formation appears to be the youngest true graptolite known to date, possibly having a stratigraphic position not far away from the Lower/Middle Devonian boundary.     

Placement of the Wenlockian/Ludlovian boundary in western New York State

Despite many years of detailed examination focused on the Silurian strata of New York State, the position of the Wenlockian/Ludlovian boundary has, to date, not been satisfactorily cstablished. Reccnt discovery of early Ludlovian graptoloid graptolites, however, provides the first conclusive biostratigraphic evidence for placement of this chronostratigraphic boundary within the New York sections. The carly Ludlovian genera Saetograptus and Spinograptus were recovered from a thin, but laterally persistent bed of argillaceous dolostone located near the base of the Goat Island Formation. This occurrencc indicates that the Wenlockian/Ludlovian boundary is at or near the contact between the Goat Island Formation and the underlying Gasport Formation, considerably lower than had previously been suspected. □ Silurian, Wenlockian, Ludlovian, graptolites, stratigraphy. biostratigraphy.     

浙江安吉志留纪真盔甲鱼类一新属

记述了浙江安吉地区志留纪真盔甲鱼类一新属——安吉鱼(新属)(Anjiaspis gen.nov.)。新属的主要特征是:中背孔呈纵长的滴水形,前端稍尖,距离头甲吻缘较远,后端圆钝,明显位于两眶孔前缘连线之前;眶孔较小,位置十分靠近头甲中线,并距离头甲后缘较近,眶孔前区长于眶孔后区;松果孔大致位于两眶孔中心连线上;感觉管系统大致呈格栅状分布,可见4条纵行干管及联络它们的横行管,横行管由侧横管和中横联络管组成,其数目均比较多;鳃囊6对,纹饰为均匀分布的细小粒状瘤点。在此基础上运用分支系统学的方法对其系统位置进行了探讨,结果表明,新属代表了真盔甲鱼类的最原始类型。     

The fine structure of the virgular apparatus in Cystograptus vesiculosus

Fragments of a virgular apparatus (nematularium), assigned to Cystograptus vesiculosus (Nicholson 1868), etched out of calcareous intercalations of early Llandoverian age from the South Urals, were investigated with the TEM and the light microscope. The extrarhabdosomal portion of the nematularium is a three-vaned, single-walled structure, built exclusively of fusellar tissue without any cortical covering. Its surface is free of cortical bandages. No traces of an extension of the nema (virgula) proper were found at the junction of all three vanes. The membranous portion of each vane is made of narrow, densely packed strips set at 6–12^o to its thickened rim. These microfusellus-like units show highly characteristic undulations of their outer pellicle, providing an additional reinforcement of the structure. Thickened rims are made by the merging of numerous microfuselli which, in their outer part, have a pellicle with a thick outer lamella. A reconstruction of the fine structure of the nematularium is suggested and possible explanations of its morphogenesis and function are discussed. Graptoloidea, nematularium, nema, virgula, ultrastructure, morphogenesis, function, early Llandoverian, southern Urals.     

Bryozoan palaeoecology in the Late Silurian of Gotland

The present paper deals with the ecology of the Bryozoa in the Upper Wenlockian of Gotland. The Upper Wenlockian sedimentary rocks of Gotland, locally known as the Halla-Mulde Beds, are deposited in a shallow sea. The sedimentary rock types include well-developed reefs of “barrier” and “fringing” types and marly limestones in both forereef and backreef positions. These sedimentary rocks are rich in Bryozoa as well as in other shelly fossils. Twenty seven bryozoan species have been identified from this stratigraphic sequence. The bryozoans tend to occur in associations. These are not strictly comparable with the neontological animal communities in the Petersen sense, but should rather be regarded as “ecozones”.Twelve different faunistic associations can be identified in the investigated material. On Bryozoa alone, five major zones are discernible.     

海南岛早志留世晚期腕足类Xinanospirifer的发现--兼论南好组

海南岛保亭县毛感乡南兵至南好公路边南好组以往被确认为下石炭统岩关阶 ,并认为与其下的上志留统足赛岭组呈角度不整合接触。著者最近在该剖面南好组中发现兰多维列世特里奇期晚期 (LateTelychian)Xi nanospirifer腕足动物群和三叶虫Latiproetuscf.latilimbatus,证明久归于下石炭统岩关阶南好组的地质时代应改归于早志留世 (Llandoverian) ;海南岛地区在早志留世明显属于扬子地台区的范畴 ;从地质时间上还暗示南好组与其下伏的足赛岭组不可能存在角度不整合接触 ;     

Algae as depth indicators in the Silurian of the Oslo region

Specimens of Girvanellu sp. are described for the first time from the Oslo region, Norway. The specimens discussed here occur in Lower Llandoverian biomicrites in the central part of the Oslo region (Bærum/Asker). The distinct association between Girvanella sp. and other faunal elements in the succession provides important new information on the depth ranges of Lcwer Silurian brachiopod communities.     

Silurische Halysitidae (Coelenterata,Tabulata) von Bithynien (Nordwest-Türkei) und biofazielle Beziehungen der Gondwanischen Halysitinae und Cateniporinae

From the Silurian (Wenlockian?) of the “Halysites” -Limestone (Dolayba-Limestone), NW-Turkey,Catenipora minuta Stasinska undCatenipora crassaeformis n. sp. are described.Halysites longicatenus Weissermel is redefined. Faunal relations of Ordovician-Silurian Halysitidae from Gondwana are subject of discussion.     

Evidence of non-vascular land plants from the early Silurian (Llandoverian) of Virginia,U.S.A.

Evidence is presented for the earliest known occurrences of non-vascular land plants and of higher, septate fungi. Macerates of carbonaceous silstone lenses from the lower Massanutten Sandstone, early Silurian (Llandoverian) of Virginia, have yielded a diverse assemblage of microfossil elements. Parallel aligned, banded tubes with annular to spiral ribbing and rounded to papilliform ends, membranous cellular sheets, cuticles, trilete spores, small spore tetrads, and septate higher filamentous fungi were recovered from the macerates. The banded tubes are probably a significant analogue with supportive or conductive cell types, but are not considered tracheidal. The heterogeneous plant assemblage may represent a thalloid, non-vascular land plant, in part, with a tubular-filamentous (nematophytic) organization associated with a membranous cellular layer and cuticular covering. While no spores were established as nematophytic, the presence of trilete spores adds to the indirect evidence of multiple evolutionary convergence toward land-plant characters. This assemblage is interpreted as of land-plant origin, based on the inferred fluvial depositional model of the fossiliferous rocks. A glacio-eustatic sea-level drop in the late Ordovician is suggested as a stimulus to the advent of land plants in the early Silurian.     

Extinction and opportunistic evolution among late Wenlock graptolites

The late Homerian was a time of profound importance to graptolites. Following the complete extinction of Cyrtograptus and the near extinction of Monograptus (s.s.)at the end of the lundgrenitestis Zone(lower Homerian, upper Wenlock), the morphologically simple and long-ranging Pristiograptus dubius lineage underwent rapid (opportunistic) cladogenesis during the succeeding upper Homerian. Two clades, each with novel and sometimes complex sicular and thecal structures, appeared. One clade, the 'Pristiograptus' praedeubeli group, gave rise to similar but more complex species, such as ' P.' ludensis and 'P.' deubeli , which in turn gave rise to Ludlow taxa, including Saetograptus (s.l.) and Pseudomonclimacis. The other clade, the Lobograptus group, gave rise to Ludlow taxa Lobograptus, Neolobograptus, Bohemograptus , and Neocucullograptus some with very complex thecal structures. Ludlow and younger monograptid faunas therefore comprise at least three separate lineages: Monograptus (s.s.), the Lobograptus group (clade), and the 'Pristiograptus' praedeubeli group (clade). Cladogenesis, evolution, extinction, Homerian, PRISTIOGRAPTUS, LOBOGRAPTUS     

Silurozodus,new genus,the oldest known member of the Trigonioida (Bivalvia,Mollusca)

The trigonioid bivalveSilurozodus gotlandicus n. gen. et n. sp. is described in terms of functional morphology, ecology, and life habit. The excellently preserved material has made it possible to reconstruct the nature of the foot and its muscles and the position of the gills.Silurozodus gotlandicus is interpreted to have been a nonsiphonate, actively burrowing, infaunal suspension-feeder that lived in a high-energy and unstable environment.Silurozodus gotlandicus is of late Wenlockian (Homerian) age and is the oldest known representative of the Trigonioida. It is probably ancestral to all younger members of this order.     

Dating of graptolite zones by sedimentation rates: implications for rates of evolution

Preliminary determinations of ancient pelagic sedimentation rates agree with modern rates at about 4 meters per million years. By combining data on the thickness of graptolite zones from the North American Cordillera with data from other parts of the world, we have refined the Early Silurian time scale and obtained much better resolution than is possible for radiometric dates. The new Early Silurian time scale allows estimation of true rates of change in graptolite diversity. The Llandoverian diversity explosion is twice as rapid as was previously thought. The brevity of diversity lows and rapidity of speciation support modern theories of quantum evolution.