摘要:

Sufficient material has been assembled to restore the powerful pectoral girdle and large fore limbs ofPlatypterygius australis(M'Coy). A reasonable approximation to the line of action of dorsal and ventral muscles which principally affected the trim of the low‐set fin‐blades was along the middle of the fin. Increased tension brought the fin‐blades nearer horizontal (to a diving position) and varying amounts of relaxation during forward movement allowed mainly water resistance to increase the tilt. The flexible blade edges were crucial in this. Unequal tension on the blades would have caused turning of the animal with whatever rapidity was desired. Allowing both fin‐blades to rise together to stalling point could have checked the animal abruptly as it struck prey. Large relative and absolute increases in the portions of the coracoids adjacent to the median symphysis highlight the relative development of young individuals. Positive allometric growth in this area stopped quite suddenly as the animals approached 6 m total length, leaving only general size i

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01713.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.tb01714.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Log‐probability curves of grain‐size distribution have been analysed of sediments collected in three previously described localities occupied by eitherLingula anatinaorL. reevei(Brachiopoda, Inarticulata). The grain‐size population transported by saltation (average about 92–223 μm), generally associated with traction load population, determinesLinguladistribution. The two preferential substrates of both studied species (density>100 individuals/m‐2) are compact and stable sediments under moderate water currents: either coarse sands and gravels clogged by fine and very fine sands, or fine, very fine and clay sands (saltation populations more than 60%). As soon as the suspension population and/or traction increase in the sediment to the detriment of the saltation population, the density ofLinguladecreases rapidly. Nevertheless, if grain‐size distribution and populations have a primordial function forLingula, other ecological features (i.e. the environmental fauna, high occurrence of digging species, the available nutrients) will affect the distribution and sometimes become prevailing. The absence of important changes in the shell shape ofLingulasince its origin suggests that the grain‐size requirements remained

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01715.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.tb01716.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

A duplicature with a very broad inner calcified lamella is revealed in representatives of the genusJanischewskyaBatalina 1926. The presence of this structure necessitates the elimination ofJanischewskyafrom the family Hollinidae. A new family of unknown ordinal disposition – Janischewskyidae – is erected. At present, a duplicature is ascertained in four groups of Palaeozoic ostracodes – Podocopina, Parapodocopina,Selebratina‐Coryellina, Janischewskyidae. □stracoda, Janischewskyidae, inner calcified la‐mella, Ca

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01717.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The minor elements Sr, S, K, Mg, Fe, and Mn were detected by election microprobe EDS (electron dispersive spectrometer) in small regions of the skeletal tissue of the Triassic spongesSestrostomella robusta(Zittel),Hartmanina involuta(Klipstein),Atrochetetes mediusCuif&Fischer,Ceratoporellasp., andEudea polymorpha(Klipstein) from Alpe di Specie (St. Cassian Beds, Dolomites, Italy). Data were compared with analyses of the modern spongesAstrosclera willeyanaLister from the Mozambique Channel andCeratoporella nicholsoni(Hickson) from the Bahamas. Sr content in Triassic sponges (mean value 9,300 ± 600 ppm) is similar to the Sr content of Recent samples (mean value 8,500 ± 1,500 ppm). This concentration of Sr shows very slight biochemical fractionation like oolitic aragonite. It is therefore possible to infer that the Triassic sea of the St. Cassian Beds had the same Sr/Ca ratio and equal aragonitic depositional conditions as those presently found in the Bahamas and the Channel of Mozambique, i.e. warm shallow waters. Generally, we did not observe a preferential distribution of minor elements with respect to structure. Only when a lower concentration in the center of spherules is observed does a preferential distribution pattern seem to exist. This could mean an initial stage of Sr leaking indicative of an incipient diagenetic process (excluding experimental errors or morphological effects). Excluding these exceptions, the Alpe di Specie spongial fauna is surely diagenetically unaltered. The Sr content shows that the micritic microstructure ofEudea polymorphais not due to a diagenetic process either. The constant, clearly detectable occurrence of sulphur (mean value 1,000 ppm) was observed. In addition, the S content was found to be linearly correlated with the strontium content. Sulphur is probably of primary organic origi

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01718.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

An electrophoretic survey of enzyme variation demonstrates that the genomes of three populations of the inarticulate brachiopodLingulacontain a higher level of variability than the average for marine, tropical invertebrates, and for other brachiopods. Genetic distances between populations from localities up to 1200 km apart were very small, indicating that the populations belong to a single species,L. anatinaLamarck. These data suggest that larval dispersal is capable of maintaining a homogeneous gene pool over this range. It is predicted that the dispersal mechanism is sufficiently efficacious to ensure gene‐flow throughout most of the Indo‐West Pacific distribution ofLingula.Further investigations of genetic distance should support the hypothesis, based on studies of adult and larval morphology, that many presently recognized species should be reassigned toL. anat

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01719.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.tb01720.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Amino‐acid analysis of the extracellular skeleton (coenecium) of two pterobranchs (Hemichordata)Rhabdopleura normaniandCephalodiscus (C.) hodgsonishows that both contain considerable quantities of collagenous material with relatively high hydroxyproline and low hydroxylysine levels. The appearance of the fibrous material in the skeleton of pterobranchs, although collagenous, differs from standard EM characteristics of collagen. The identification of the collagenous nature of the pterobranch skeleton with the presumed presence of collagen‐like material in the periderm of fossil graptolites, taken in conjunction with other data, supports the hypothesis that both groups may be closely related phylogenetica

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01721.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Examples of the trilobitesToxochasmops extensus(Boeck, 1838),Asaphiscus wheeleriMeek, 1874,Encrinurus mitchelliFoerste, 1888,Ogygopsis klotzi(Rominger, 1887),Paradoxides davidisSalter, 1863 andOryctocephalusspp. which are interpreted as exuvial configurations, are described. Four specimens ofToxochasmops extensusarc known in which the pygidium rests either directly behind the eephalon, or with only three intervening thoracic segments. It is considered that during exuviation the old pygidium became wedged behind the cephalon. This facilitated its removal. An ecdysial configuration ofAsaphiscus wheeleriis described which possesses inverted and partially rotated free cheeks. In addition, part of the thorax of the specimen is wedged obliquely behind the cephalon. This is considered to have aided withdrawal of the trilobite from its old exoskeleton. Two specimens ofEncrinurus mitchelli aredescribed which possess free cheeks inverted beneath the cranidium by lateral rotation, in a manner similar to that ofA. wheeleri.Three examples ofOgygopsis klotziare described, one a failed exuvia and two in which the free cheeks were inverted and rotated through 180° with respect to their original position and came to rest beneath the thorax. An identical exuvia ofParadoxides davidis trapezopygeis also described. Two specimens ofOryctocephalusexhibiting two different arrangements of inverted free cheeks are recorded. Possible mechanisms for each of these free cheek inversions are proposed

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1984.tb01722.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY