摘要:

The type materialof Eoconularia loculata(Wiman, 1895), a conulariid with high, bifurcated septa, was originally found in an erratic boulder, hence the source‐rock is as yet unidentified. Recently, a rich material of the species has been discovered at eleven localities in the Silurian Hemse Beds of Gotland Another two localities in the Slite Beds (Wenlockan, Sheinwoodian) revealed what is assumed to be the ancestor ofE loculata.This ancestral form probably constitutes a separate taxon distinguished fromE. loculatain having simple, unbranched septa.E. loculatais re‐described, and four ontogenetic stages in septal development are recognized. During stage 1, the most juvenile stage, the septa are simple. The septa in stages 3 and 4, the adult stages, are coarse and bifurcated. The affinities of conulariids are discussed, with the conclusion that the group shares a number of similarities with modem scyphomans. The microstructures of the exoskeleton show several similarities with coronatids, and the septa are interpreted to be homologous with the internal structures of stauromedusids. The stratigraphical distribution of all currently known septate conulariids suggests that septa were a primitive morphologic feature ranging from early? Ordovician to late Silurian. The simplest type, however, persisted at least into the early Permian. Five of the eleven described septa types have been found only among the conulariids from Gotland. □Conulariida, EOCONULARIA LOCULATA, bifurcated septa, taxonomy, ecology, morphology, Scyphozoa, Sweden, Gotland, Sil

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01562.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Review of Smith, A. B. 1994: Symstematics and the Fossil Record: Documenting Evolutionary Patterns. 223 pp. Blackwell Scienfific Publications, Oxford

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01563.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The late Homerian was a time of profound importance to graptolites. Following the complete extinction ofCyrtograptusand the near extinction ofMonograptus(s.s.)at the end of thelundgrenitestisZone(lower Homerian, upper Wenlock), the morphologically simple and long‐rangingPristiograptus dubiuslineage 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’ praedeubeligroup, gave rise to similar but more complex species, such as ‘P.‘ ludensisand ‘P.‘deubeli, which in turn gave rise to Ludlow taxa, includingSaetograptus(s.l.) andPseudomonclimacis.The other clade, theLobograptusgroup, gave rise to Ludlow taxaLobograptus, Neolobograptus, Bohemograptus, andNeocucullograptussome with very complex thecal structures. Ludlow and younger monograptid faunas therefore comprise at least three separate lineages:Monograptus(s.s.), theLobograptusgroup (clade), and the‘Pristiograptus’ praedeubeligroup (clade).Cladogenesis, evolution, extinction, Homerian, PRISTIOGR

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01564.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01565.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The changes in the sicula of Early Devonian monograptid graptolite populations show a pattern that is described as punctuated stasis: two longer periods of stasis separated by a transitional population of shorter duration between them. The pattern differs from punctuated equilibrium in that anagenesis is involved rather than cladogenesis. The pattern has been observed in several widely separated areas (Nevada, Thuringia, Poland, Ural Mountains) and is an example of collateral evolution in graptolites. In this case, the collateral morphologic change occurs relatively rapidly in a large, globally distributed taxon. The study permits accurate correlation of the horizon of appearance ofMonograptus hercynicusPemer in the upperdelta Zone(conodont zonation) of late Lochkovian age (Devonian) on a global scale. The partial integration of these two biostratigraphies constrains correlations between the shelly, shallow‐water biofacies and the deeper graptolitic biofacies. The pattern of punctuated stasis has been discovered in Lower Devonian strata of central Nevada, where 22 horizons in sequence were sampled. Statistical analyses were performed on 13 characters encompassing measurements of the sicula, thecae, and rhabdosome. Most of these characters do not exhibit sustained trends or punctuated changes. However, sicular width exhibits an abrupt increase over a short stratigraphic interval and is used to classify members of the group into four quantitatively defined morphotypes. This natural perturbation in the pattern of change is used to divide the lineage into paleospecies. This makes the segments of the lineage easy to identify and imparts stability to the classification and precision in biostratigraphy. The variation studies enable the ranges of the morphotypes to be used to further subdivide the stratigraphic record of the late Lochkovian. □Graptolites, Devonian, Lochkovian, evolution, punctuated stasis, biostratigraphy, MONOGRAPTUS, phylog

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01566.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The growth and function of the conodont skeletal apparatus have important implications for early vertebrate relationships and the evolution of vertebrate hard tissues, yet they are poorly understood. Analysis of element length, platform linear dimensions, and platform area in discrete Pa elements of CarboniferousIdiognathodusandGnathodus bilineatusreveals that the platform increased in size at a rate significantly above that required to maintain geometric similarity. Measurements of P, M and S elements in bedding‐plane assemblages ofIdiognathodusand G.bilineatusindicate that relative to Pa element length, Pb and S element growth was isometric, whereas M elements grew with negative allometry. There is no evidence to support loss or resorption of S and M elements in later growth stages, or to indicate periodic shedding and replacement of elements. These results are important for understanding apparatus and element Function. The positive allometry of the Pa element platform supports interpretations of a mashing or grinding tooth‐like Function for platformed Pa elements. If conodonts were active suspension‐feeders, the increasing food requirements of a growing conodont would require the filter array formed by the S and M elements to have grown at a rate significantly above isometry. The lack of positive allometry of S and M elements indicates that conodonts were not suspension‐feeders and supports hypotheses that conodonts fed with a raptorial apparatus and teeth. □Conodonts, vertebrates, skeletal apparatus, ontogeny, allometry, function, suspension‐fee

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01567.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The skeletal architecture of conodonts of the order Prioniodinida Sweet, 1988, is poorly understood. Undisturbed or slightly disturbed natural assemblages are rare. A three‐dimensional apparatus plan has been constructed using scale models of the elements ofIdioprioniodus, based on late Mississippian and late Pennsylvanian (Carboniferous) assemblages from Montana and Illinois, USA. The interpretation of the architecture is based on symmetry relationships between the various elements. A revised element notation scheme is proposed for the apparatus. □Conodonts, apparatus, palaeobiology, Prioniodinida, Idioprionio

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01568.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Instances of convergence or parallelism among unrelated Lower Carixian ammonites are not uncommon. The case of polymorphitid‐like ammonites is considered here, and the example ofCoelocerasis investigated in detail. The small sexual dimorph (microconch) ofCoeloceras pettos(Quensitedt) (Coeloceratidae), a progenetic species, provides a remarkable example of complex convergence with the microconch ofUptonia(Polymorphitidae). Homeomorphic morphology is here an amalgam of juvenile traits, of maturation‐related transformations, and of completely new features bearing no obvious relation with either progenesis or maturation. A stratophenetic approach is hardly adequate for unravelling such an involved pattern of convergence. However, a cladistic analysis of ammonoid morphology suggests thatCoeloceraswas derived from the TethyanMiltoceras.Indeed, greater biostratigraphic knowledge and the independent use of comparative shell morphology are both needed to improve ammonite phylogeny. □Convergence, parallelism, progenesis, dimorphism, ammonites, Jur

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01569.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Radiocarbon dates provide a means for estimating the time a shell may persist in active sedimentary environments and the actual temporal extent of time‐averaging in marine deposits. Information compiled from the published literature on the radiocarbon age of marine shells gave information on a total of 734 radiocarbon dates from 276 localities from nearshore (10 m depth) habitats. The median age of 128 nearshore shells is 2,465 years; that of 158 shells from the shelf is 8,870 years. The distribution of shell ages in both nearshore and shelf environments is strongly skewed: most dates are in the 0–3,000 range, and the number of shells in older age‐classes falls off rapidly. The maximum age of a shell in an active sedimentary environment is a measure of time‐averaging, because it estimates the amount of time represented in the deposit. The median duration of time‐averaging in 63 nearshore deposits is 1,250 years; the median duration of time‐averaging in 129 shelf deposits is 9,190 years. Radiocarbon‐dated shells from fossil deposits confirm our estimate of time‐averaging in nearshore environments: the median difference between maximum and minimum ages in 49 inactive beach ridges is 1,390 years; the median difference in other, predominantly nearshore deposits, is 830 years. Greater shell survival and longer durations of time‐averaging in shelf settings may result from lower rates of sedimentation, lower rates of taphonomic destruction, greater rates of bioturbation, the history of post‐glacial sea level, sample bias, or some combination of these factors. Our results may estimate the actual magnitude of time‐averaging of shelly deposits forming under conditions of low net sediment accumulation. Such extensive time‐averaging may confound attempts at detailed paleoecological and paleoenvironmental reconstruction. □Time‐averaging, benthic assemblages, taphonomy

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01570.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Lingulate brachiopods are described from the Upper Cambrian ‐ Lower Ordovician (Tremadoc‐Arenig) of Scandinavia (Sweden, Denmark, and Norway), South Ural Mountains, northeastern Central Kazakhstan, and the southern Kendyktas Range in southern Kazakhstan. The faunas comprise a total of 56 species of which 20 are new these are assigned to 40 genera, of which the lingulidsAgalatassiaandKeskentassia, the siphonotretidSiphonotrerella.and the acrotretidsGalinella, Longipegma, Ottenbyella, Akmolina, Mamatia, Sasyksoria, andOtariellaare new. The new Subfamily Elliptoglossinae is proposed. The poorly known Cambrianardovician stratigraphy of the South Urals. northeastern Central Kazakhstan, and the southern Kendyktas Range is reviewed. Many sequences in these areas that were previously referred to the Upper Cambrian and Tremadoc can now be correlated with the lower Arenig Hunneberg Stage in Baltoscandia. Three main types of faunal assemblages can be distinguished: (1) theBroeggeriaassemblage; (2) several microbrachiopod assemblages; and (3) theLeptembolon‐Thysanotosassemblage. TheBroeggeriaassemblage is distributed world‐wide in the Tremadoc of the southern Kendyktas Range, Scandinavia, Belgium, Great Britain, Canada, and Argentina, while theLeptembolon‐Thysanotosassemblage is confined to the Arenig of an area surrounding the East European platform, including northern Estonia, Poland, Germany, Bohemia, Serbia, and the South Urals. The microbrachiopod assemblages are known mainly from the Upper Cambrian ‐ Arenig of Scandinavia, South Ural Mountains, northeastern Central Kazakhstan, and the southern Kend

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1994.tb01571.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY