摘要:

The Middle Ordovician reefs of Norway were the first to develop in the western part of the Balto‐scandian epicontinental sea and are the earliest coral‐stromatoporoid reefs so far reported in Europe. Small patch reefs in the Steinvika Limestone, Langesund‐Skien district, consist mainly of algae, echinoderms, corals and stromatoporoids. Bryozoans, molluscs, arthropods and brachiopods are also present. The reefs developed on pelmatozoan‐rich substrates and are organically zoned, consisting of a pioneer community of stemmed echinoderms and sheet algae, a high‐diversity intermediate community dominated by fasciculate corals and a low diversity climax community of massive corals and stromatoporoids. These communities are interpreted as the seral stages of an autogenic ecological succession. Small patch reefs are also present in the laterally equivalent Mjøsa Limestone, Toten and Nes‐Hamar districts. These are organically very similar to those in the Steinvika Limestone and developed in an identical way. A large complex, consisting of several reefs, is also present in the Mjøsa Limestone. Unlike the reefs elsewhere, which developed within shallow inshore areas, this complex developed at the outer edge of the inshore shelf. The outstanding feature of the complex is the main reef forming the offshore limit which is totally dominated by stromatoporoids and lacks a sequential development. This is due to the influence of the harsher environment at t

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01688.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Echinosphaerites, known from the Lower and Middle Ordovician, has branched biserial brachioles. Such features are so far unknown in the Rhombifera.Echinosphaeriteshad a skeletal meshwork like that of other blastozoan echinoderms, with a fine outer mesh layer and an inner coarse mesh layer. During evolution the number and location of brachioles, including the pattern of brachiole branching, changed by increase in the number of brachioles and increased complexity of the branching pattern. The exothecal pore structures increased in the complexity of patterns of tangential canals. The pattern of skeletal growth inEchinosphaeritesis discussed. The Echinosphaeritidae and Caryocystitidae families are closely related and show parallel development.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01689.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The Upper Kimmeridgian—basal Tithonian clastic sequence at Santa Cruz, Estremadura, represents environments ranging from river channels and flood plains to lagoons and protected bays showing a deltaic influence. Within the marginal marine environments, five benthic macroinvertebrate associations are recognized and analysed in terms of diversity and species composition. All five are thought to be controlled largely by salinity and to represent lowered and/or fluctuating salinity regimes. They can be grouped along a salinity gradient in which theMesosaccella dammariensis—Corbulomima suprajurensisassociation, occurring in prodelta silts and marls, represents the closest approach to fully marine conditions and in which theEomiodon securiformisassociation, typical of delta front sands, extends into the oligohaline regime. Banks of theIsognomon lusitanicumassociation and patch reefs of thePraeexogyra pustulosa—Nanogyra nanaassociation are thought to be typical of brachy‐to mesohaline conditions occurring in brackish bays and lagoons. Characteristic of the latter salinity regimes is also theJurassicorbula edwardiassociation. The integrated approach, using benthic faunas, trace fossils and sedimentological data, leads to a detailed interpretation of the sedimentary sequences and the construction of a biofacies model which can also be used for other parts of the Lusitania

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01690.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01691.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Scanning Electron Microscope study of the exoskeletal ultrastructure of secondarily phosphatized material ofFlexicalymenesp. from the Upper Ordovician Maquoketa Shale, Iowa, USA, shows that the exocuticle, comprising 20% of the total exoskeletal thickness, is composed of horizontal laminar units between 0.2 and 1 μm thick. These units consist of primarily mineralized organic fibres which form horizontal laminae interconnected by inter‐laminae. The endocuticle is considerably more mineralized than the exocuticle, and its original organic structure cannot be observed in untreated preparations. Etching with chromium sulphate reveals: (1) horizontal organic laminar units, 0.2 to 2 μm thick, and (2) pore canals with non‐twisted walls about 0.3 μm in diameter. Exuvia cannot be distinguished from the exoskeletons of dead animals. The exoskeletal ultrastructure in trilobites agrees essentially with that in crust

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01692.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The enigmaticOrestoviafrom the Lower Devonian of Siberia has a vascular cylinder of spiral and annular tracheids, external and internal cuticles in the cortex, and stomata. Abundant spores are occasionally preserved between the cortex cuticles. The ‘reticulate structures’ are thyriothecia of a hemisphaeriacean fungus. Spores of several types are found sticking to the cuticle.Orestoviacan be conceived as a transitional form between the alga‐likeProtosalviniaand the sporangiate vascular plants. The origin of land plants is disc

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01693.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Analysis of some phylogenetically important stages in the evolution of graptoloids, articulate brachiopods, and the earliest mammals suggests that large scale evolutionary progress did not proceed linearly but that biological improvement was stepwise, achieved by rapidly crossing successive functional thresholds which were interpolated between gradual morphological changes (here termedproximations) towards the condition at which the structures became predisposed to the next threshold crossing. Crossing of many functional thresholds involved morphological discontinuities or functional instabilities that had to be bridged abruptly, over dithyrial populations. The principle of scalariform evolutionary progress is believed to be of fairly general application, but our current ability to analyse many critical evolutionary events in functional terms is still at a primitive stage because the functional significance of many important morphological changes are unclear. It is stressed that the evolutionary success of any ‘hopeful monster’ is determined at the population level, and that therefore, if extreme cases are discussed, the emphasis must be on ‘monstrous fami

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1981.tb01694.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY