The fourth series of the Silurian System in Podolia

The Skala horizon of Podolia has been under discussion as a possible candidate for the stratotype of the fourth Silurian series (primary subdivision) in the international standard chronostratigraphical scale. After a brief survey of the history of investigation, the section through the basal boundary of the Skala horizon is fully documented. The lithostratigraphy, biostratigraphy, and correlation of the Skala horizon are then discussed.     

The Downton Series as the fourth Series of the Silurian System

A review of lithofacies and fossil distributions in the Downton strata of the Welsh Borderland and Wales indicates that these beds form a suitable basis for definition of a chronostratigraphical division of Series rank within the Silurian System. The basal boundary stratotype for the Downton Series is defined at the base of the Ludlow Bone Bed Member of the Downton Castle Sandstone Formation in a section at Whitcliffe Road, Ludlow. Shallow water marine sediments span the boundary, with no evidence of a measurable time break. Correlation of the base of the Downton Series from eastern North America through Baltoscandia and Poland suggests that it lies at or very close to the base of the Monograptus ultimus Biozone and thus approximates to the base of the Přiacute;dolí beds of Bohemia. This paper formed a submission to the Subcommission on Silurian Stratigraphy in May. 1981. □ Silurian, Downtown Series, standard subdivision, lithostratigraphy, biostratigraphy, chronostratigraphy, correlation.     

中国香辛料产品加工标准体系研究

在调研和综合分析我国香辛料产品加工现状基础上,根据标准化原理和标准化体系研究方法,首次系统地对我国香辛料产品加工体系进行研究,用三维坐标形式全面展示加工体系的层次、产品门类和过程要素之间的关系,体系表中的262项香辛料加工过程控制标准,为香辛料提供可靠的过程质量保障.     

Predation in the Ordovician and Silurian of Baltica

Signs of predation appear in the Middle Ordovician of Baltica. Shell repair dominates over the predatory borings in the Ordovician and Silurian. Predators attacked molluscs, brachiopods and tentaculitoids in the Ordovician and molluscs, tentaculitoids, brachiopods and ostracods in the Silurian. There is an increase in the number of prey species in the Late Ordovician, which could be related to the Great Ordovician Biodiversification Event. Molluscs are the favourite prey taxon in the Ordovician, but in the Silurian, molluscs became less dominant as the prey. This is probably not an artefact of preservation as Ordovician and Silurian molluscs are equally well preserved.     

山西省小麦生态区划

从具有完整气象资料的62个县中选取与小麦生产有关的9个地理、气象因子,6个品种和栽培因子,采用对应分析方法将全省小麦分为三大麦区：（1）晋南冬麦区,（2）晋北春麦区,（3）晋中和晋东南冬麦及冬春麦交界区.三大麦区又可分为11个副区．部分地区修改了传统区划的界线用数学方法分区的界线与现场考查结果一致．三大麦区与全国麦区划界一致．     

Phylogenetic analysis of the Silurian Retiolitidae

A cladistic, phylogenetic analysis of the Retiolitidae, using 18 genera and parataxa and 23 characters, reveals that two distinct clades can be recognized within this family, as well as a primitive stem-group that includes the genus Pseudoretiolites . One of the derived clades includes Pseudo-plegmatograptus, Stomatograptus and Retiolites , which are assigned to the revised subfamily Retiolitinae. The other derived clade, the early part of which shows a paraphyletic relationship, includes the remaining known genera Rotaretiofites s.l., Paraplectograptus s.l., Sokolovograptus, Plectograptus, Agastograptus, Spinograptus, Gothograptus, Eisenackograptus, Neogothograptus, Semiplectograptus, Plectodinemagraptus and Holoretiolites . These genera are all included within an expanded Plectograptinae. The biostratigraphic distribution of these taxa suggests that these two clades diverged from a Pseudoretiolites-like ancestor in mid-Aeronian time.     

Regional integration of evidence for evolution in the Silurian Pentamerus-Pentameroides lineage

Under ideal conditions, the stratophenetic test for phyletic gradualism in fossil lineages requires nearly continuous samples of time-specific populations through rock sequences representing geologically significant periods of time. Shifting environments account for one source of 'imperfection' in the local rock record. Few species are sufficiently eurytopic to survive changing environments in a given region over a long time span. Where marine fossils are involved, independently correlated sea-level curves may be used to patch together segments of stratigraphic sections from different regions that collectively encompass the uninterrupted environment of the target species. In the Lower Silurian of Iowa, stratigraphic gaps among test samples for phyletic gradualism in pentamerid brachiopods occur wherever pentamerid communities are succeeded by deeper water stricklandiid communities or by shallower-water coral-algal communities. Correlation of sea-level curves indicates that water depth was consistently shallower in the northern Great Lakes area. Usually when stricklandiid communities replaced a pentamerid community in Iowan seas, contemporaneous pentamerid communities replaced a coral-algal community in Michigan or Ontario seas. Temporal meshing of samples from Iowa and the northern Great Lakes area (based on congruent Stricklandia and Eocoelia lineage zones) supports the hypothesis that Pentamerus oblongus evolved to Pentameroides subrectus through a gradual narrowing and loss of divergence in its outer plates. A transitional morphotype between the two genera (from the Lower Silurian of Alabama) is illustrated. □ Phyletic gradualism, punctuated equilibria, Brachiopoda, Pentamerida, Silurian, North America.     

Comparison of Conventional Methods, the R/B System, and Modified R/B System as Guides to the Major Divisions of Enterobacteriaceae

Primary grouping of more than 2,000 members of Enterobacteriaceae, freshly isolated from clinical specimens, was performed on the basis of eight conventional laboratory tests used routinely in this laboratory and by the R/B system. Results indicate that both systems perform well in this first step in the identification of various medically significant species of the family. Difficulties encountered with certain reactions of the R/B system were corrected with a physical modification of the tubes. An additional 100 representatives of Enterobacteriaceae were compared with conventional methods and the modified R/B system. Results indicate improvement in observing and interpreting findings with the R/B system.     

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.     

TDM1 Regulation Determines the Number of Meiotic Divisions

Cell cycle control must be modified at meiosis to allow two divisions to follow a single round of DNA replication, resulting in ploidy reduction. The mechanisms that ensure meiosis termination at the end of the second and not at the end of first division are poorly understood. We show here that Arabidopsis thaliana TDM1, which has been previously shown to be essential for meiotic termination, interacts directly with the Anaphase-Promoting Complex. Further, mutations in TDM1 in a conserved putative Cyclin-Dependant Kinase (CDK) phosphorylation site (T16-P17) dominantly provoked premature meiosis termination after the first division, and the production of diploid spores and gametes. The CDKA;1-CYCA1.2/TAM complex, which is required to prevent premature meiotic exit, phosphorylated TDM1 at T16 in vitro. Finally, while CYCA1;2/TAM was previously shown to be expressed only at meiosis I, TDM1 is present throughout meiosis. These data, together with epistasis analysis, lead us to propose that TDM1 is an APC/C component whose function is to ensure meiosis termination at the end of meiosis II, and whose activity is inhibited at meiosis I by CDKA;1-TAM-mediated phosphorylation to prevent premature meiotic exit. This provides a molecular mechanism for the differential decision of performing an additional round of division, or not, at the end of meiosis I and II, respectively.     

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.     

Status of Divisions of the International Geologic Time Scale

Each chronostratigraphic unit of the International Geologic Time Scale will be defined at its base by a Global Stratotype Section and Point (GSSP) or Global Standard Stratigraphic Age (GSSA). Nearly 50 GSSPs and 10 GSSAs have now been ratified. Ideally, the GSSP coincides with events having a global correlation potential. The international stage divisions of some systems, such as the Jurassic or Neogene, are similar to traditional usage in European geology. However, in order to utilize global correlation horizons, the international stage divisions of other systems, such as the Ordovician or Permian, have required assembling new stage nomenclatures or hybrids of different regional stages. A reference table by the International Commission on Stratigraphy itemizes the current or potential GSSP and GSSA definitions of all international geologic time units.     

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.