摘要:

The paper describes a new member of a group of Lower Palaeozoic marine fossils which partly bridge the gap between echinoderms and chordates. Evidence suggests that this group included the ancestors of the vertebrates. Its members are traditionally regarded as primitive echinoderms, but are better seen as primitive chordates with echinoderm affinities. They form a basal subphylum of chordates‐the Calcichordata Jefferies 1967. The Calcichordata, in accordance with an early suggestion by Gislén, are probably ancestral to all living chordates.The new calcichordate is namedReticulocarpos hanusigen et sp. nov. It comes from the Lower Ordovician Šárka Formation (Llanvirn) of Šárka near Prague, Czechoslovakia and is placed in the family Amygdalothecidae Ubaghs 1970. It is important because of its position in the Calcichordata. This group is divided into two very different orders–the Cornuta and the Mitrata. The Cornuta are the more primitive order and gave rise to the Mitrata, which had the structure of giant, calcite‐plated tunicate tadpoles. Many features show that the new species is a very advanced cornute, closely related to the stock that gave rise to the mitrates. For this reason it is important in the general history of the chordates, since some primitive mitrate was probably the latest common ancestor of the living chordate subphyla i.e. of tunicates, of amphioxus and its allies and of the vertebrates.Being a mitrate‐like cornute, the new species allows the cornutes and mitrates to be compared more confidently than before. Four results are especially important. Firstly it is likely that the stem (=tail) of mitrates is equivalent only to the anterior part of the stem of cornutes. This is significant, because traditional views as to which was the upper surface in mitrates have been based on stem homologies now seen as false. SecondlyReticulocarpos hanusiis adapted to stay up on very soft mud, using only the strength of the mud for support. The mitrates, on the other hand, supported themselves on soft mud by a much more reliable method resembling buoyancy. Thirdly, the new form had paired transpharyngeal eyes which are otherwise known only in mitrates, and which are the earliest type of paired eyes in chordates. Fourthly, it becomes possible to homologize the thecal plates of cornutes with those of mitrates.Reticulocarpos hanusirepresents an important phase in chordate evolution dominated by the necessity of staying up on mud by a very precarious method. During this phase many pre‐adaptations for swimming were acquired. Primitive mitrates, descended from a very similar form, were probably the first chordates t

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1972.tb00691.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

During 1960‐69, observations were made of flowering, fruiting and foliar activity of 61 canopy trees (representing 45 species) in a largely undisturbed tract of Hill Dipterocarp Forest. Rainfall was measured by an accumulating gauge and, at a nearby station, the number of rainy days recorded. Annually recurrent floral cycles were displayed by only ten species. In these and in 11 additional species, foliar cycles were also circannual. Gregarious flowering, apparently in response to drought, occurred in many species in 1963 and 1968. In other years, interspecific differences in periodicity maintained a minimal incidence of flowering at 44%, and fruiting at 27% of species in the sample. Despite specific variations in phenology, the community as a whole exhibited regular seasonality, with single annual peaks of flowering and fruiting and a double peak of leaf productio

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1972.tb00692.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The fine structure of the mouthparts of the collembolanFolsomia Candidais described, largely on the basis of a study with the scanning electron microscope. The structure of the maxilla and of die mandibular molar plate is clarified and its interpretation corrected. The grinding function, usually attributed to the collembolan molar plate is disputed. This possible change in function of the mouthparts may also mean that these insects play a slightly different role than hitherto believed in the breakdown of the litter and humus in the soil.An alternative method to replace freeze‐drying in the preparation of Collembola, and possibly other small arthropods for scanning electron microscope studies is describe

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1972.tb00693.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY