Silurian Chitinozoa from the type Wenlock and Ludlow of Shropshire,England

Chitinozoa recorded from the Wenlock and Ludlow from the type areas in Shropshire and other localities in the Welsh Basin are listed, and the ranges of 35 taxa of stratigraphic value plotted.     

A conodont, thelodont and acanthodian fauna from the Lower Přídolí (Silurian) of the Much Wenlock area, Shropshire

Conodonts, thelodonts and acanthodians have previously been collected from the P?ídolí of Shropshire (Welsh Borderland) from bone beds such as the Ludlow Bone Bed. In general, specimens collected from these types of deposit are very abraded and make taxonomic studies difficult. This contribution describes well preserved thelodont microelements from two samples from the Downton Castle Sandstone Formation (P?ídolí, Silurian) of the Much Wenlock area of Shropshire. Head scales, a wide variety of transitional scales, and pore scales of the lateral line sensory canals of the thelodont Paralogania ludlowiensis (Gross) are described for the first time. A new acanthodian Nostolepis linleyensis sp. nov. and elements from the apparatus of the conodont Ozarkodina?hemensis sp. nov. are documented from the same samples. The thelodonts in both samples are typical of upper Ludlow–P?ídolí faunas from across the Welsh Borderland, and are also present in smaller numbers in the Ludlow Series of Gotland, Sweden, Saaremaa Island, Estonia, and in Latvia and Lithuania. The conodont O? hemensis sp. nov. is restricted to the Much Wenlock area of Shropshire. The co-occurrence of well preserved elements of conodonts and thelodonts suggests that they were deposited fairly rapidly with little or no re-working and that a restricted marine environment prevailed in the early P?ídolí in the Much Wenlock area of Shropshire.     

Some Silurian Brachiopods from Lithuania and Their Palaeobiogeographical Significance

Silurian brachiopods are described from 21 boreholes in Lithuania. Nine genera are recognized and represented by one or two species, including the atrypids Atrypoidea, Cromatrypa, Lissatrypa and Septatrypa, athyridids Collarothyris, Nucleospira, Meristina and Pseudoprotathyris, and rhynchonellids Ancillotoechia and Plagiorhyncha. Two new species, Cromatrypa? pubes and Lissatrypa lithuanica, are described. The same taxa are reported from England, Gotland, Belarus and Podolia in Wenlock and Ludlow strata, and from Podolia, Urals, the Canadian Arctic archipelago and Russian Arctic islands in Prídolí strata.     

Silurian (Ludlow) acastid trilobites from Gotland and Scania,Sweden

Acastid trilobites from Ludlow strata on Gotland include three stratigraphically non-overlapping species ofAcastella Reed:Acastella madidipes n. sp. (Hemse Marl and Eke Beds),A. breviceps (Angelin 1851) (Burgsvik Beds), andA. amatrix n. sp. (Hamra Beds, and probably Burgsvik Beds). Type and other material ofA. breviceps (Angelin) from the Klinta Formation, Scania, is revised. Meraspid and early holaspid material ofAcastella is described. Some characters supportAcaste and allied taxa of mostly Wenlock age as a monophyletic subfamily Acastinae.Acastella as widely recognized is a grade with Devonian species more closely related to Asteropyginae than to the Ludlow type species. Baltic Ludlow-P?00ED;dolí species previously placed inScotiella Delo form a distinct group,Ewacaste n. gen., that includes a species from the uppermost Eke Beds on Gotland.     

Microplankton associations, biofacies and palaeoenvironment of the type lower Ludlow Series, Silurian

The acritarchs and prasinophyte algae from the type lower Ludlow Series of the Goggin Road section, Ludlow, England, are resolved into seven recurrent associations comprising taxa with similar environmental preferences. Endemic and environmentally sensitive associations of acritarchs and prasinophytes are identified and high-resolution fluctuations in the early Ludlow palaeoenvironment are established. An early Ludlow crisis in the acritarchs is recognized in the lower part of the Middle Elton Formation, when an abrupt palaeoenvironmental change in the Ludlow area resulted in a large decline in the abundance of the acritarchs, but allowed Tasmanites and retiolitid graptolites to flourish briefly. Cymbosphaeridium sp. A, Pulvinosphaeridium ludlowense and Multiplicisphaeridium arbusculum forma A are taxa possibly specialized, or produced as a response, to a stressed palaeoenvironment, as they are most abundant when other acritarchs and prasinophytes are uncommon. The low abundance of acritarchs and prasinophytes in the Upper Elton Formation may be related to high sedimentation rates and to the slumping of sediments caused by instability on the shelf of the Welsh Basin, or to lower plankton productivity.     

The nautiloid cephalopod Order Endocerida in the Silurian

The rare Silurian representatives of the Order Endocerida are reviewed, described afresh, and illustrated. The Welsh Llandovery speciesTretoceras bisiphonatum is assigned to the order. Canadian Llandovery to Wenlock forms,Cameroceras hudsonicum and species ofHumeoceras, complete the record as presently known.     

Symbiotic interactions in the Silurian of Baltica

Thirteen symbiotic associations occur in the Silurian of Baltica. Symbiosis was especially prominent among colonial animals, most commonly with stromatoporoids. These sponges hosted the most diverse fauna of endobiotic symbionts (including rugosans, Syringopora, ‘polychaetes’, cornulitids and lingulids). This pattern can be explained by the abundance of stromatoporoids in the Silurian of Baltica and their large skeletal volume, making them attractive hosts for smaller invertebrates. There is an evolutionary trend of an increasing number of different pairs of symbiotic taxa from the Llandovery to the Ludlow, with a remarkable increase in the Ludlow. This is likely related to an increase in the number of mutualistic taxa that could have had evolutionary advantages over organisms less amenable to symbiosis. The number of different pairs of symbiotic taxa also increased in the Wenlock, which may be linked to delayed recovery from the end‐Ordovician mass extinction.     

Wenlock carbonate,level bottom,brachiopod-dominated communities from Wales and the Welsh Borderland

Four marine level bottom communities are described from Wenlock carbonate rocks (i.e. the Wenlock and Woolhope limestones) of Wales and the Welsh Borderland. The communities are: (1) Sphaerirhynchia wilsoni, (2) Isorthis clivosa, (3) Eoplectodonta duvalii, and (4) Visbyella trewerna. The Sphaerirhynchia wilsoni community is divided into: (a) an argillaceous micrite phase, and (b) a biomicrite phase. The communities and the phases are defined on the basis of consistent and recurrent numerical species combinations.The community spectrum from Sphaerirhynchia wilsoni to Visbyella trewerna is broadly correlated with an increase in water depth. The communities show no correlation with major limestone facies types. It is suggested that turbulence, rates of sedimentation and substrate type are some of the environmental parameters, in the shallow near-shore regime, which determine the distribution of brachiopods.     

Silurian-Devonian miospores from the western and central Algeria

The age of Rock Units B1 and B2 of the Middle Silurian-Lower Devonian of Sahara (Algeria) is assessed and confirmed as late Homerian to ?earliest Lochkovian on the basis of moderately well preserved miospore assemblages. The data upon which this age assessment is provided by recent palynological studies in the Cantabrian Mountains (NW Spain), the type Wenlock area, Shropshire (England), south and south-west Wales, the Midland Valley of Scotland and the Ghadames Basin, Libya. Quantitative study shows that cryptospores decrease in number and variety upwards, laevigate miospores are prevalent and the representatives of the rugulate, crassitate genus Scylaspora are dominant. The occurrence and range of these species as well as other miospore taxa recorded during this study provide the basis for recognizing three miospore assemblage and one interval biozones, namely Scylaspora vetusta-Scylaspora kozlica, Chelinospora sanpetrensis-Cymbosporites triangulatus, Chelinospora hemiesferica and Scylaspopra radiata-Apiculiretusispora synoria. Of these biozones, two assemblage biozones are proposed as new. Core samples of Rock Unit B1 from borehole NGS-1 of the Triassic Province contain the oldest two miospore assemblage biozones. Rock Unit B2 from the boreholes GMD-2, ISS-1 (Tidikelt Plateau) and NGS-1 (Triassic Province) comprise the youngest two miospore biozones. The assemblage and interval biozones allow inter-regional correlation with latest Middle Silurian to probably earliest Devonian strata. The inadequacy of coverage of core samples result in the absence of critical palynological evidence, to determine the exact position of the base of the Ludlow, Pridoli and Lochkovian. Comparison with the zonal and sub-zonal divisions of Mid-Palaeozoic sequences from other parts of the world shows crucial differences in the distribution of the spore flora within Gondwanan and Euramerican regions during Pridoli and early Lochkovian. Six new miospore species namely Retusotriletes delicatus nov. sp., Scylaspora cymba nov. sp., S. distincta nov. sp., S. radiata nov. sp., S. undulata nov. sp. and Cymbosporites triangulatus nov. sp. are described. Three more possibly new miospore forms are described and illustrated but not specifically named.     

A Wenlock ancestor of the micropoma phylogenetic lineage

A new graptolite species, Monoclimacis praemicropoma , from the Upper Wenlock of Poland is described. It is an ancestor of the Lower Ludlow M. micropoma (Jaeckel). The phytogeny of the praemicropoma-micropoma lineage is discussed. M. micropoma nannopoma (Jaeger) has been assigned to a separate evolutionary lineage. Graptolites, Wenlock, phytogeny .     

Sea level and faunal change during the late Wenlock and earliest Ludlow (Silurian): A point of view from the Algerian Sahara

A late Wenlock transgression (C. rigidus zone) affecting a large area of the Algerian Sahara has been known for the last thirty years; in this case there is no break at the Wenlock‐Ludlow boundary and the sedimentation is continuous to the earliest Ludlow. But in many other areas of Sahara a late Wenlock regression is observed. This regression may or may not be followed by a latest Wenlock or an early Ludlow transgression. A sedimentary model is proposed in despite of several problems. In order to compare what happens in each region a schematic diagram is used showing the tendencies to shallowing and deepening. Differences observed between the North Sahara basin and the other parts of the Algerian Sahara and comparison between local sea‐level curves and the global sea‐level curve proposed by Johnson et al. (1991) lead to reconsider the evidence of an eustatic early Ludlow event. To end the problem of the disappearance of nearly all graptolites at the end of Wenlock is discussed. The influence of land emergence in the evolution of marine fossil groups in the disturbance that it can bring to the development of the microplankton and the chemistry of the sea seems to have been too neglected.     

A diverse assemblage of early land plants from the Lower Devonian of the Welsh Borderland

FANNING, U., EDWARDS, D. & RICHARDSON, J. B., 1992. A diverse assemblage of early land plants from the Lower Devonian of the Welsh Borderland. Nine rhyniophytoid taxa are described from an early Gedinnian locality ( middle micromatus-newportensis spore Biozone) near Ludlow, England. They include Cooksonia pertoni, C. hemisphaerica, C. cambrensis, Tortilicaulis transwalliensis and three new taxa, Salopella marcensis sp. nov., Uskiella reticulata sp. nov. and Tarrantia salopensis gen. et sp. nov. Isolated sporangia of reniform shape, and those subtended by short lengths of axis, contain spores of Apiculiretusispora type and may belong to C. caledonica or Renalia . Morphologically distinctive forking, terminal sporangia lacking identifiable spores are not placed in a new taxon, because evidence based on in situ spores from elsewhere suggests they may belong to Salopella . Structures previously interpreted as clusters of sporangia of Yarravia- type are shown to be ± globular sporangia longitudinally split into valves. Sterile axes are dominated by smooth forms; although rare examples possess small enations. Tracheids have not been seen in axes of fertile specimens nor in sterile coalified compressions. A single pyrite permineralization contains tracheids of zosterophyll type. The assemblage demonstrates diversity among rhyniophytoids in the early Devonian and the existence of low vegetation 'alongside' the much larger zosterophyll dominated type.     

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.     

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.     

Late Silurian trilobites from the Nuratau and Turkestan ranges, Uzbekistan and Tajikistan

Silurian trilobites of Ludlow and P?ídolí age are described from sections in southern Uzbekistan and from adjacent parts of Tajikistan. They belong to 22 species (10 named and 12 under open nomenclature) distributed among 13 genera belonging to the families Proetidae, Tropidocoryphidae, Aulacopleuridae, Scharyiidae, Cheiruridae, Encrinuridae and Odontopleuridae. The following new species are described: Interproetus pentaxus, Paleodechenella turkestanica, P. zaaminicus, Cromus tamchii and Leonaspis nuratensis. The generic associations from the mid Ludlow bear a striking resemblance to coeval ones from Bohemia, and include genera otherwise known only from that region or from adjacent parts of central Europe. The trilobite faunas from the late Ludlow and P?ídolí series are much less diverse and are dominated by genera of the Warburgellinae (Tropidocoryphidae), which include one species common to Vaigatch Island in the Russian Arctic, and Podolia, Ukraine. The closest links of the diverse central Asian mid Ludlow faunas are therefore to central Europe, whilst the sparser younger Ludlow and P?ídolí faunas, such as they are, suggest closer links to Baltica.     

Strophomenidae,Leptostrophiidae, Strophodontidae and Shaleriidae (Brachiopoda,Strophomenida) from the Silurian of Gotland,Sweden

Twelve species of Brachiopods are described from the Silurian of Gotland, six furcitellinines and six “strophodontids.” One is new—Strophodonta hoburgensis n. sp. The furcitellinines are moderately common and diverse in the lower part of the succession, but the last species disappears in the middle Hemse beds (~middle Ludlow). Three genera are represented: Bellimurina, Pentlandina and Katastrophomena, with the species and subspecies B. wisgoriensis, P. tartana, P. loveni, P. lewisii lewisii, K. penkillensis and K. antiquata scabrosa. Most of the taxa are confined to low energy environments, but P. loveni was evidently specialized for the high energy reef environments of the Högklint Formation. B. wisgoriensis displays environmentally induced morphological variability in developing strong, frilly growth lamellae in high-energy environments. The “strophodontids,” although belonging to three different families, share a common morphology consisting of denticles along the hinge line, a semi-circular outline, unequally to finely costellate ornament and, most importantly, a concavo-convex profile with both valves of the same curvature, enclosing a very small body chamber. Two leptostrophiids are generalists, occurring in both high- and low-energy environments and with long stratigraphical ranges [Mesoleptostrophia filosa; latest Llandovery through the entire Ludlow. Brachyprion (Brachyprion) semiglobosa; latest Llandovery to latest Wenlock]. The third leptostrophiid (Brachyprion (Erinostrophia) walmstedti) is short ranged and occurs in low-energy environments in the latest Llandovery. The species belonging to the Strophodontidae (Strophodonta hoburgensis n. sp.) and Shaleriidae [Shaleria (Janiomya) ornatella and S. (Shaleriella) ezerensis] occur only in high-energy environments and have a short range within the late Ludlow.     

An association between the stromatoporoid Diplostroma yavorskyi Nestor and calcareous algae from the Much Wenlock Limestone, England

Intergrowths of the stromatoporoid Diplostroma yavorskyi Nestor with calcareous algae are described for the first time from the Much Wenlock Limestone of Wenlock Edge, England. The intergrowth developed as irregular. nodular growth-forms which initiated around a nucleus of biomicrite sediment or skeletal clasts. The paired stromatoporoid laminae characteristic of this species form regular alternations throughout substantial portions of the skeleton with the calcareous algae Girvanella sp., Rothpletzella sp., Wetheredella sp. and Rhabdoporella sp., and micrite. Nodular growths developed as a result of intermittent rolling on the sea floor. The nature of the periodic intergrowth of different taxa suggests that the stromatoporoid grew on firm substrates by lateral growth at an edge zone. Epiphytes encrusted areas of the stromatoporoid skeleton devoid of soft tissue. □ Stromatoporoid. calcareous algae. epiphyte. intergrowth. Wenlock.     

Upper Silurian microplankton of the Leintwardine Group, Ludlow Series, in the type Ludlow area and adjacent regions

The acritarchs and prasinophyte algae from the Upper Bringewood, Lower Leintwardine, Upper Leintwardine and Lower Whitcliffe formations of the Ludlow type area and surrounding regions are described. The following new taxa are proposed: Cymatiosphaera pumila sp. nov., Melikeriopalla pustula sp. nov., Cheleutochroa beechenbankensis sp. nov., Cymbosphaeridium molyneuxii sp. nov., Flammulasphaera bella gen. et sp. nov., Percultisphaera incompta sp. nov., Salopidium aldridgei sp. nov. and Umbellasphaeridium? wicanderi sp. nov. A holotype is defined for Lophosphaeridium galeatum Hill and a further 34 new taxa are described under open nomenclature. Two biozones, identified by the first appearance of the zone taxon, are defined in the Sunnyhill section, Ludlow [Global Stratotype Section and Point (GSSP) for the base of the Ludfordian Stage, Ludlow Series]. The base of the Leoniella vilis Biozone is identified at 4.52m below the top of the Upper Bringewood Formation at Beechenbank, Aymestrey. The base of the Triangulina sanpetrensis Biozone is identified at 15.49m above the base of the Lower Leintwardine Formation and Ludfordian Stage at the Sunnyhill section. These biozones allow correlation with sections in north–west Spain, Podolia and Gotland. The possibility of using Visbysphaera whitcliffense and U.? wicanderi as biozonal indicators is suggested.     

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.