摘要:

The diverse brachiopod faunas from the Calcaire de Ferques of north France and the Lime Creek Formation of Iowa show a remarkable homeomorphy. They are both of Frasnian age and occupied similar mid‐shelf muddy carbonate environments. It is possible to match species in the two faunas on external form; this similarity can also be seen in the population histograms. The two areas originated in different faunal provinces, however, and serial sections show that homeomorphic forms were not genetically related. Thus it seems possible that the similarity between the two faunas is entirely a result of adaptation to similar environment

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01878.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01879.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Detailed examination through a continuous stratigraphic interval representing nearly the entire Lower Devonian Onesquethawan Stage shows that the presence and size of the trace fossilZoophycosvaries systematically throughout the unit. The lithofacies of this sequence are interpreted to represent a double offshore‐nshore cycle. Both maximum and mean diameters of theZoophycosweb (=spreite) are relatively large within a more offshore setting and become progressively smaller towards both margins of this geographic (= stratigraphic) zone. Close inspection ofZoophycosmorphology reveals a nearly perfect correlation (r = 0.96) betweenZoophycosweb diameter and meniscus height. Meniscus height bears a constant relationship to the maximum body diameter of the animal creating the burrow, consequently, size of the web is directly proportional to body size. Thus the animal is largest near the center of its environmental range and smallest near the margins. Other ichnofossils in the section (Scalarituba, Phycodes, Chondrites), measured on a more limited scale, show similar size variations with smaller forms at the margins of their respective ranges. Therefore, trace fossil size may be a sensitive indicator of paleoenvironmental gradient

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01880.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01881.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

In the light of recent applications of equilibrium theory to palaeoecological investigation, the origins and scope of the model are reviewed as a perspective for considering the viability of such applications in the analysis of Ordovician faunal associations. Alternative methods for the detection of immigration and emigration patterns are advanced in favour of other recently proposed techniques. The mid‐Caradoc Gelli‐grin Formation is used as an example of a well sampled fossiliferous deposit from which comprehensive faunal data can be derived for use in the detection of intra‐association fluctuations in faunal composition. Different methods of defining such fluctuations are shown to produce consistent results. ‘Saturation’, ‘area effect’ and ‘overshoot effect’ are all shown to be aspects of equilibrium theory with potential for application in the palaeoecological field. The calculation of the coefficient of variation for eight faunal associations discussed here is shown to be a useful method for the determination of the degree of saturation of such associations; comparable associations show similar

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01882.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01883.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The larval development of hyolithids is inferred to have been closely similar to that of primitive gastropods. A trochophore‐like larva produced a swollen initial conch and a convex operculum. The initial conch was either subsphaerical and smooth or fusiform with a pointed apex and growth lines. This is taken to indicate an initial development within egg covers or free‐living, respectively. A pelagic veliger phase followed. preceded by hatching in the first case. Veliger shells are similar to adult ones. Metamorphosis (transformation of veliger into benthic adult animal) in both hyolithids and gastropods was accompanied by an increase in mortal

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01884.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01885.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A diverse group of LudlovianMonograptusspecies is characterized by the retarded growth of thecal hoods, either proximally [M. colonus(Barrande),M. chimaera(Barrande) andM. hauptiKühne] or throughout the rhabdosome [M.micropoma(Jaekel)]. In all these species the hoods are secondary structures, i.e. later growth additions to the thecae. By contrast, in the DevonianMonograptusspecies the thecal hoods are primary structures, i.e. the outward extension of the dorsal thecal wall. and are formed by undelayed growth that typically is completed before growth of the succeeding theca begins. It is among Ludlovian (M. uncinatusTullberg) and Pridolian (M. simihPřibyl) forms with homologous hoods that the roots of the majority of the DevonianMonograptusspecies might be found. The LudlovianM. micropomaandM. hauptishould not be affiliated to the group ofMonograptus vomerinus(Nicholson), which is highly characteristic of, and restricted to, the late Llandovery and Wenlock graptolite fauna

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01886.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The biological organization of ammonites does not permit a true inversion of suture lines to occur. However, the complex pattern of the ammonite phragmocone ‐ nacreous septa, membrane coverings, siphuncle, and soft body ‐ does show ‘weak points’ in growth regulation. This provides several instabilities which lead to a pseudo‐inversion caused by mechanical compression of th

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01887.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY