摘要:

The paleoecologist must be able to distinguish a transported assemblage from an in situ one. A method is proposed to assess whether the post‐mortem transport of individuals affected their observed spatial (horizontal) distribution. The spatial distribution of a species can be random or contagious. The spatial distribution of individuals of a species in the death assemblage produced by the cumulation of many temporally discrete inputs will be random if the individual inputs are random and contagious if the inputs are contagious. The spatial distribution patterns of several species should not covary in the absence of physical disturbance regardless of their own distributions, however. The degree of covariance between individuals of several species of similar hydrodynamic propensity is dependent on the amount and intensity of postmortem movement. The more species that covary, and the larger the size classes that covary, the more likely that transportation played an important role in the species' distribution patterns. Conversely, the absence of covariance suggests that, for at least some species, biological factors determined the species' spatial distributions. Similarly, covariance of vertical distribution patterns might suggest homogenization. by bioturbational or physical mixin

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01895.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

When tied shut, three genera of punctate terebratulids from the Northeast Pacific[Terebratulina unguicula(Terebratulidina),Terebratalia transversaandLaqueus californianus(Terebratellidina)] take up O2from the external water (at one‐third the rate when gaping). The impunctate rhynchonellidHemithiris psittaceadoes not, indicating that punctae admit O2when the valves are closed. The shells ofT. transversavary from smooth and globose toSpirifer‐like alate and costate morphs. The latter have more punctae and greater uptake of O2through the shell. The alate/costate morphs are most abundant where turbidity is likely to prompt closure. Punctael respiration is faster through the thin shells ofLaqueusthan the thick ones ofTerebratalia.O2deprived articulates gape widely and close slowly when disturbed, but there is no evidence of O2debt. They regulate O2consumption at the same rate from saturation to 0.5 ml·l1, and thus appear adapted to low O2levels. These results have implications for the energetic efficience of articulates and the evolutionary patterns of bivalve molluscs v. articul

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01896.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01897.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The Late Ordovician bryozoan genera of central and southeastern North America are geographically distributed in three biotic provinces, separated by boundaries reflecting major lithofacies differences. The central Cincinnati Province contains most of the North American endemic genera, and represents a narrow ecological zone separating the clastic wedges of the marginal Reedsville‐Lorraine Province from the cratonic carbonate platform of the Red River‐Stony Mountain Province. The provinces provided major life zones, or biomes, for each of the five bryozoan orders. Genera comprising the provinces differed as well in morphologic complexity, geochronologic survivorship, tiering, endemism and eurytopy. Regions on either side of the Cincinnati Province were dominated by inferred immigrants from Baltoscandia. Al‐logenic provincial succession produced time‐averaged mixed faunas in regions near the provincial boundaries. Although most generic originations took place within the Cincinnati Province, evolutionary novelties are associated with the Reedsville‐Lorraine Province. The loss of the diverse Cincinnati Province, connected with global cooling and a eustatic lowering of sea level, may have been a chief factor in the Late Ordovician extinction of bryozoan genera. Genera from the Red River‐Stony Mountain Province differentially survived into t

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01898.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01899.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Certain ichnogenera from the Podhale Flysch Basin do not occur randomly, but are grouped in distinct horizons, which are useful in mapping. The position of certain tuffite beds proves an approximate isochronism of those trace fossil horizons. Changes of the life conditions, among them especially oxygenation of the sea bottom, were responsible for that ichnologic differentiation. Profuse Occurrences ofTaphrhelminthopsisare mainly connected with the presence of lighter, bluish shales, which indicates a well‐oxygenated bottom. More distal and frequent sedimentation of turbidites could positively influence the preser‐vational potential of the surface forms (very good state of preservation ofTaphrhelminthopsissuggests that preservation of surface forms was frequent in the flysch basin), but the O2condition was the main controlling factor for the occurrences of ichnofauna. Most discriminating were trace makers of pre‐depositional (mud‐dwelling)Taphrhelminthopsis, and they were most probably irregular echinoids, while soft‐bodied trace makers of pre‐ and post‐depositionalPlanolites(post‐depositional means sand‐dwellers) were the most tolerant ones. An increased level of biological activity connected with a shift in the OMZ could have been the reason whyTaphrhelminthopsisbecame so profuse in one period. Concerning preservational problems, some complications in determining pre‐ and post‐depositional forms in the case of composi

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01900.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Eldredge, N.&Stanley, S. M. (eds.) 1984: Living Fossils. (Casehooks in Earth Sciences; series Editor R. N. Ginsburg.)

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01901.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

A rich material of echinoderm fragments from two Middle Cambrian stratigraphical levels on Bornholm are preserved due to phosphatization of the original calcitic stereom. Preservation of echinoderms in this way ‐ not previously recorded from the Middle Cambrian ‐ permits detailed analysis of the three‐dimensional stereom structure. Identifiable are fragments of stylophorans and eocrinoids. Stem columnals, most likely from eocrinoids, show a wide and advanced morphological variation indicating articulation similar to that of crinoids. The material from the Exsulans Limestone/Kalby marl (Ptychagnostus gibbusZone) represents stem‐bearing cystoids older thanAkadocrinusfrom Bohemia. The Andrarum Limestone (Sole‐nopleura brachymetopaZone) contains echinoderm fragments from a higher stratigraphical level, a level correlatable with that from which the oldest North American stem–bearing cystoid,Eustypocystis, has be

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01902.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Cilia‐generated flow in the absence of ambient current is directed from frontal to reverse sides of branches inBugula turrita, B. turbinata, B. neritina, andB. stolonifera, whether axes of feeding lophophores are perpendicular to the basal plane of branches or are tilted toward distal ends of branches. Ambient current less than 5 cm per second interacts with cilia‐generated flow, but ambient flow of 15 cm per second destroys self‐generated colonial flow and severely hampers feeding. Polypides are located in the more distal, younger portions of colonies, in species with and without polypide recycling, whereas zooids in the more proximal, older portions are senesced. Presence of feeding polypides in distal but not in proximal portions of the larger spiralled colonies ofB. turritaandB. turbinataresults in downward, slightly radially directed flow through the colony. The colonial flow passes directly from one whorl to the next‐proximal so that water exits from low around the colony perimeter, and a proximally expanding conical stagnant zone occupies the interior of the colony. A substantial percentage of zooecia in distal whorls of well‐preservedArchimedesis filled by sediment and inferred to have been occupied by actively feeding polypides. whereas spar‐filled zooecia capped by terminal diaphragms were apparently senesced during the latter part of a colony's existence. The capped zooecia constitute an increasing percentage of the total in more proximal whorls. Generally similar colony form and inferred similarity in distribution of current‐generating polypides in spiralled colonies ofBugulaand inArchimedessuggest that colony‐generated flow inArchimedeswas similar to that inBugula, passing downward and then outward, and only through the distal whorls

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01903.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb01905.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY