摘要:

Among the various kinds of biostratigraphic units, lineage‐zones are especially interesting and meaningful, not only in stratigraphy but also in evolutionary biology. The chronological shift of morphology in evolution is fundamentally uninterrupted, but sometimes it seems discontinuous or even saltational. Such breaks have been commonly attributed to gaps in sedimentation, but could be explained, at least in some cases, by more essential mechanisms of evolution. The difference in the patterns of morphological change may be primarily related to the nature of non‐sex‐associated genetic variation. continuous or discontinuous, as well as the strength of selection pressure. Some theoretical models for phenotypic substitution are presented here in terms of population genetics, though these are not the only possible explanation for breaks in fossil re

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00908.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The paradigm method involves comparing fossil organs with theoretical structures (paradigms) which are 100% efficient in performing proposed functions. Applications of the method have been criticised as being unsystematic and mechanistic, producing conflicting results and ignoring pertinent limitations. Selected interpretations of zigzag slits and spines in brachiopods and bivalve molluscs are re‐examined. None invalidate the method. The last step in paradigm analysis, i.e. selectingthemost appropriate function, is a major weakness and should be avoided. Repeated paradigm analysis may be used to interpret evolutionary trends in terms of adaptation and functional efficienc

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00909.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00910.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

M. J. S. Rudwick and others postulate ‘rhythmic‐flow’ feeding for the Permian richtho‐feniacean bi‐achiopods, whereas R. E. Grant claims that they fed by normal ciliary action. Suspension‐feeding has two components, current generation and food capture; normal brachiopod lophophores do both, but this is neither universal nor compulsory among animals. Opening and closing the richthofeniid shell generated a ‘tidal‐flow’ current precisely analogous to respiratory currents in mammals; this is neither inefficient nor ‘self‐defeating’, as Grant claims. Grant's analysis fails because he chose the wrong mechanical analogy (a pump). Morphological features of richthofeniids are better explained on a tidal‐flow hypothesis than on a ciliary‐flow model, and all the data adduced by Grant in rejecting the former is compatible with it or favorable to it. It explains morphological features that are bizarre mysteries on the ciliaiy‐current model, and is therefore superior even though it implies that these Permian brachiop

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00911.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

This paper is a reply to criticism presented by C. R. C. Paul and R. Cowen in immediately preceding articles in Lethaia. Contrary to the assertion by Paul, the present author did not reject the paradigmatic method but (1)criticizedit for its limitations and seemingly erroneous results, (2)appliedit to the richthofeniacean and lyttoniacean brachiopods by use of the pump as paradigm, and (3)extendedit to include anatomic, metabolic, and phylogenetic considerations that go beyond the structural and mechanistic constraints of the original formulation. The rhythmic flow mechanism was rejected primarily on the basis of evidence for a ptycholophous lophophore in the Productidina. and the relative inefficiency of ‘valve flapping’ in contrast to ciliary action in pumping nutrient‐bearing fluid into the shell. A Chinese blast furnace was claimed by Cowen to employ a single oscillating panel as a pump, but instead this panel must act as a valve that admits air in surges while the draft in the furnace maintains unidirectional flow through the system. This is analogous to ciliary feeding in brachiopods, where undirectional flow is maintained by ciliary pumping, and the valve opens to admit water. A richthofeniid with aCompositaentrapped beneath the apertural meshwork is introduced as additional evidence against the likelihood of ‘valve fl

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00912.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00913.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The production and preservation of trilobite resting and furrowing traces is discussed with special reference to specimens from Upper Cambrian strata in North Walcs, Spain, and Poland. Resting excavations are attributed largely or completely to animal activity, and do not normally rcsult from currcnt scouring. Resting excavations, furrows, and many other trace fossils are formed at the sediment‐water interface and not bencath a thin sand layer or by burrowing between beds. The factors which allow the initial production of the traces on the ocean floor muds (e.g. cohesion, shear strength, low pore water pressures) will also favour their preservation during deposition of the casting san

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00914.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Many measuring devices used in micropaleontology are unsatisfactory because observations must be recorded manually. Moreover, most use a linear scale that depends on the presence of predetermined morphological loci. An x, y recorder, largely adapted from instruments available in geological laboratories, is discussed. It obviates manual recording, frees data collection from the constraint of homologous loci and. in some applications, permits more shape information to be collected.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00915.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00916.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Ludlovian limestone at Ljugarn, Gotland. repreqents a shallow marine environment of stromatoporoid biohenns and flanking areas of mud and stromatoporoid debris. Brachiopods were restricted to surfaces of the debris deposits.Lissatrypa sulcata, a smooth atrypacean, dominated the brachiopod fauna, with individuals living beak downward in high density clusters, developing weaker pedicle attachment and a sulcus during ontogeny. Surrounding low density areas ofLissatrypaincluded small, pedicleattached, non‐sulcate shells.Howellella, Spirigerina, andMorinorhynchus?lived in isolated clusters near low densityLissatrypapopulations, and 10 other very rare brachiopod species may have been non‐reproducing members of the community. Brachiopcd species diversity, and thus number of niches, was lower in the biohermal enviroment than in bathymetrically equivalent, level‐bottom commun

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1975.tb00917.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY