摘要:

Three trace fossil associations have been identified from facies interpreted as low wave energy upper, middle and lower shoreface deposits, transitional shoreface/shelf deposits and open epicontinental shelf deposits. These were developed in pre‐regressive, regressive and transgressive phases associated with eustatic sea level changes caused by the upper Ordovician glaciation. The three associations are theSkolithos‐Diplocraterionassociation, theDiplichnites‐Phycodesassociation and theThalassinoidesassociation. TheSkolithos‐Diplocraterionassociation inhabited upper, middle and lower shoreface environments, theDiplichnites‐Phycodesassociation a lowermost shoreface environment and theThalassinoidesassociation inhabited offshore epicontinental shelf environmcnts.The Skolithos‐DiplocraferionandDiplichnites‐Phycodesassociations bear strong affinities with previously describedSkolithosichnofacies assemblages (indicating shoreline environments) and theCruzianaichnofacies forms (indicating shallow water environments down to wave base) respectively. TheThalassinoidesassemblage, however, closely compares with assemblages described from Mesozoic epicontinental shelf sequences. Trace fossil diversity achieves a maximum in the lowermost shoreface environment and reduces in deeper water and shallower water environments. This accords with diversity patterns identified in analogous Jurassic epicontinental palaeonvironments. The stratigraphic distribution of some trace fossil association boundaries accords with those of contemporary body fossil associations. However, several body fossil associations are included within the volume of distribution of a single trace fossil assemblage. □Trace fossil association, shoreface and shelf, Oslo district, u

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01433.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01434.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The Middle and Upper Devonian carbonate succession of the Montagne Noire, Southern France has been precisely zoned by an unbroken sequence of conodont zones. Stratigraphic control is excellent, and has allowed evolutionary changes in tropidocoryphine trilobites, which occur throughout the succession, to be directly established. The tropidocoryphine had been a stable group for some 40 million years prior to the Middle Givetian. In their last few million years, however, they underwent rapid evolution and exhibit some striking transformations of the cephalon and the regression and virtual disappearance of the eye within a relatively short space of time. They also show a marked diminution in size, and lose their original relief so that the glabella becomes virtually flush with the surface. There are two separate lineages, both of which show eye‐reduction and subsequent blindness. In the earlier lineageTropidocoryphe (Longicoryphe)‐Erbenicoryphe, the main features of the ancestral rootstock are conserved and the stable, strongly divergent anterior sutural pattern of the cephalon remains the same. Theeye, however, became reduced to a slightly convex surface lacking lenses, only indistinctly defined.Erbenicorpheis confined to well‐oxygenated facies, and probably lived as a shallow burrower within the sediment; it became extinct in the early Frasnian. The second lineageT. (Longicoryphe)‐Pterocoryphe‐ Pteropariashows a remarkable backward migration of the suture, which progressively swings posteriorly in successive species spanning four Frasnian conodont zones (about three million years duration). At the same time the eye progressively degenerates so that the last forms are blind. Sutural migration and eye reduction are not genetically linked, however; the unusual form of the cephalon and suture probably resulted from an adaptation to the euxinic environment in whichPterocorypheoriginated. The loss of the eye resulted from the adoption of an endobenthic habit inPteropariawhich descended from the ancestralPterocoryphebut which had migrated to an oxygenated facies. Eye‐reduction is therefore parallel in the two lineages, but superimposed upon a different original cephalic configuration. The lastPteropariabecame extinct when the late Frasnian fauna became overwhelmed by the first pulse of the ‘Kellwasser Event’ (probably an anoxic overturn). The evolving characters, through virtually all observed steps, show progressive unidirectional change without sudden breaks or saltations. Such unidirectional evolution is an adaptive response to constant long‐lasting environmental influences. □Evolution, Devonian trilobites, France, gradua

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01435.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01436.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Pre‐Phanerozoic carbonaceous megafossils are generally considered to be the remains of metaphytic algae. While these fossils are not particularly common, they are significant for the understanding on the global evolutionary level of the pre‐Phanerozoic biota. Ribbon‐shaped vendotaenids were interpreted as brown algae and represent the youngest, most common and geographically most widespread Precambrian carbonaceous megafossils. It now appears that they may be better understood as abandoned giant sheaths of sulfide oxidizing organotrophic bacteria related to the ModernThioptocaamong the Beggiatoaceae. □Thallophyta, algae, methaphytes, Vendotaenidae, late Proterozoic, Precambrian, Vendian, b

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01437.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The International Commission on Zoological Nomenclature has given these opinions which could be of interest to palaeontologists (originally published in theBulletin of Zoological Nomenclature 46:l).

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01438.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Plaster impressions and sand casts of extant medusae, a chondrophoran, and a pennatulid share basic structural characteristics with fossils in the Upper Proterozoic Ediacara assemblage. Impressions of extant medusae and Proterozoic circular impressions show general similarities in arrangement and position of radial and concentric structures and a central raised boss. However, annular rings and radial grooves are more numerous in the Proterozoic fossils and strongly folded or deformed fossils are rare as compared with impressions of modem medusae. Recent pennatulids yield impressions that are more deformed and irregular than the Proterozoic genusCharniodiscus.The greater frequency of deformation of most simulated fossil medusoids relative to Precambrian circular impressions implies that Proterozoic medu‐soids were substantially stiffer than many modern taxa of comparable sizes. Many fossils with abundant circular rings have no constructional counterparts among the extant forms studied here and their medusoid affinities should remain in doubt. The structural simplicity of impressions of Ediacara organisms and extant cnidarians suggests that their mutual similarities may be due to convergence. However, there is no compelling morphological reason to reject the claim that some Proterozoic fossils may share affinitieswith living cnidarians. □ Taphonomy. Ediacara biota, cnidarians, phylogenetic relationsh

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01439.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01440.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The discovery of numerous distal stem fragments ofEurax marhoumensisn. sp. brings new data on the formation of the stolons and the control of stereomic secretion. The presence of primary fixations in the dististele demonstrates the composite nature of stolonifcrous scgmcnts. The creeping zone is formed by gradual incorporation of the lower columnals of the mesistele into the stolon. Stereom growth rings observed on weathered facets or transverse sections are markers of the morphofunctional evolution of the columnals during different growth stages. The fixation organs are true stereomic outgrowths without axial canal or Segmentation; they grow from a single columnal and remain in connexion with it. The morphology of stolons results partly from the topography of the substrate and partly from control by stereomic secretion which influences the columnal thickness. The introduction of wedge‐shaped columnals in curves of the stem and on the development of fixation devices. Epizoan attachment (bryozoans, corals, crinoids) induces different stereomic reaction depending on the growth stage of the crinoid column. The stereom of the host may proliferate as a sheet, abortive ossicles or shapeless stercomic masses which tend to limit the growth of the epizoans and incorporate them in the column stercom. □Crinoid, column, morphology, stereomic secretion, Devonian, Algeria.Le découverte de nombreux fragments pédonculaires distauxd'Eurax marhoumensis n.sp. apporte des données nouvelles sur le processus de la formation des stolons et sur le contrôle de la sécrétion stéréomique. L'existence de fixations primaires dans la dististéle démontre la nature composite des segments stoloniaux. Les zones rampantes se forment par incorporation progressive des columnales de la partie inférieure du pédoncule dans les stolons. Les cernes de croissance du stéréome observées sur les facettes altérées ou sur les sections constituent des témoins de leur évolution morphofonctionnelle au cours des différents stades de la croissance. Les organes de fixation correspondent à de véritables expansions stéréomiques dépourvues de canal axial et de segmentation; ils bourgeonnent àpartir d'une seule columnale avec laquelle ils rcstent en conncxion. La morphologie des stolons résultc en partie de la topographie du substratum et du contrôle de la sécrétion stéréomique qui se traduit par I'ajustement de l'epaisseur des columnales, l'introduction d'articles cunéiformes dans les courbures et le développement des organes de fixation. L'implantation d'épizoaires (Bryozoaires, Coraux, Crinoïdes) provoque des réactions stéréomiques différentes suivant le stade de croissance du pédoncule du Crinoïde. Le stéréome de I'hôte peut proliférer sous formc d'une lame, d'articles abortifs ou d'amas difformes qui tendent a limiter le développement de I'épizoaire et à l'incorporer dans le pédoncule. □Crinoïde, pédoncu

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01441.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Capillae are a major feature of the fine ornamentation in spiriferid brachiopods. Within the lower Devonian spiriferids, studied in this paper, two categories of organization can be distinguished: strictly radial orientation of the microstructures, which leads to the eospiriferid‐type of organization, and pseudoradial orientation, which provides a delthyridid‐type. Apart from this distinction, it can now be shown that the mode of development is quite different in each case. Thus, and allowing for differences in size, the capillae of eospiriferids are quite similar to the costae of costate spiriferids. On the other hand, the origin of the capillae is more complex in the delthyridids and as yet not fully known. Other factors (such as the rate of growth, the divergence angle of the capillae, etc.) have effects on the growth mechanisms and contribute to the existence of a large variety of microornaments. Furthermore. available data indicate that the divergence of the capillae is closely related to the paleogeographical distribution of the populations involved. If this observation proves valuable for the whole stock of spiriferids (s.l.), it opens new ground for paleozoogeographical investigations. □Spiriferid brachiopods, eospiriferids, delthyridids. microornament, Devonian, paleogeog

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01442.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY