摘要:

Consistent asymmetric folding of the commissure is a characteristic feature of a small but significant number of brachiopod species. The feature may be obligate or facultative and is almost entirely confined to rhynchonellids, most of which are Mesozoic. The detailed nature of the asymmetry is very variable, but does not extend to internal hard parts such as crura. Taken as a whole, asymmetric brachiopod species show no preference for any particular environment or geographic region, and in no circumstances seem to have been markedly more or less successful than symmetric species. We are thus led to suggest that asymmetry was a genetically based condition which cropped up periodically in brachiopod evolution, and which possibly was selected neither particularly for nor against.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02016.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02017.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Carbonate strata from the central parts of epicontinental seas are ideal for detailed biostratigraphic study of eustatic sea level change. Using a model for epeiric seas in which carbonate accumulation rate is depth‐dependent, we derive synthetic stratigraphies for sea level histories simulating post‐glacial transgression and constant and sinusoidally fluctuating ridge volume increase. These sea level histories give distinctively different trends for water depth as a function of stratigraphic position in sections' bathymetric curves. In general, depth is proportional to the rate of sea level rise. Depth‐dependent sedimentation leads to a time lag between sea level fluctuation and corresponding depth fluctuation which, as examples show, can approach 106years for depth fluctuations of only a few meters – a fundamental consideration in reconstructing sea level curves, time‐correlating sections by their bathymetric curves, and attempting to relate bathymetric history on continents to mechanisms driving sea level change. Bathymetric curves based on gradient analysis of fossil assemblages (coenocorrelation curves) for Middle Ordovician sections in New York and the American Midwest approximate patterns for sinusoidally increasing sea level. The model's predictions are tested in an ‘artificial experiment’ that takes advantage of differential subsidence between the craton's middle and its edge to make a difference in the bathymetric histories of sections that otherwise record the same sea level history. Depth fluctuations of no more than a few meters over million year spans are potentially useful in time‐correlation to within fractions of a cycle's period. The depth‐dependence in sedimentation was that, above wave base, net accumulation per year was very roughly three‐millionths the water depth. Association of volcanic ash layers with transitory sea level minima on the craton, and with onset of more rapid subduction in the Taconic are ‐ continent collision zone, suggests interrelationship on a million year scale between sea level and large‐s

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02018.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

A classification of marine organisms as deposit‐feeders, suspension‐feeders, carnivores, or scavengers is difficult becausc many species appear to be capable of using more than one feeding method. Thcse species are most probably ‘opportunistic’, varying their diet with local food availability. Efforts to reconstruct trophic webs and establish deposit‐feederisuspension‐feeder ratios in (paleo)faunas are seriously hampered by the presence of opportunis

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02019.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The family‐group classification of conodonts presented in the revised edition of the Treatise on Invertebrate Paleontology, Part W, Supplement 2, Conodonta, published in 1981, is shown to contain errors with regard to the International Code of Zoological Nomenclature. The classification lacks a concise philosophical and methodological foundation and exhibits very poor conceptualization of the taxa it recognizes. The classification is analyzed and discussed in terms of, among Linnkan taxonomists, generally accepted objectives and conventions with regard to the internal structure and phylogenetic message of a hierarchical natural classification. The obvious errors in terms of the ICZN are pointed out and corrected. As a demonstration of an alternative approach, a classification of the superfamilies Prioniodontacea, Hibbardellacea, and Icriodontacea is presente

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02020.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02021.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Two Cambrian lepidote metazoans known from different respective types of preservation have been compared in order to elucidate their biology and affinities. The widely distributed Lower CambrianHalkieriais represented by isolated hollow sclerites, probably of originally calcareous composition. The Middle CambrianWiwaxiais known from the Burgess Shale as isolated sclerites (scales and spines) and as more or less complete individuals. AlthoughHalkieriasclerites were mineralized and those ofWiwaxiawere probably not, there are fundamental structural and morphological similarities between the two. Both bad an imbricating scaly and spiny armour consisting of hollow sclerites with a longitudinally fibrous structure. The sclerites did not grow, but were probably moulted during the course of ontogenetic growth.HalkieriaandWiwaxiaare regarded as closely related. Both are referred to the Order Sachitida He 1980. The sclerite armour ofHalkieriais reconstructed on the template provided byWiwaxia.The interpretation of sachitid sclerites as protective armour is an alternative to the interpretation by Jell (1981,Alcheringa 5)that sachitid sclerites were respiratory organs in an animal of probable annelid affinities. Sachitids are interpreted as sluggish, benthic deposit feeders that do not belong to any recognized phylum.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02022.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02023.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Specimens originally illustrated from Lower Cambrian rocks of the Sierra Morena in Badajoz and Sevilla Provinces, southwestern Spain are supplemented by new material from another locality and are described asScenella morenensisn. sp. AlthoughScenellawas originally considered to be a patelliform gastropod, for three decades now the genus has been classified as a monoplacophoran. The type species ofScenella, S. reticulataBillings, does not show any paired muscles scars, nor does this new species; such scars are indicative of the Monoplacophora. This new species ofScenelladoes exhibit features which suggest assignment to the chondrophorine coelenterates. If so,Scenellacannot represent the ancestral form of mollusk.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb02024.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY