首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
    
During the Mississippian (Tournaisian), numerous crinoid genera of the subclass Camerata evolved exaggerated anal tubes, cylindrical extensions of the tegmen with the anus at the distal end. Additionally, camerates exhibit higher frequency of platyceratid gastropod infestation than any other crinoid clade leading some researchers to speculate that anal tubes evolved in response to platyceratid parasitism. To test the infestation avoidance role of anal tubes, platyceratid distribution was analyzed among 636 tubed and 675 tubeless crinoids from Mississippian strata in North America. Results demonstrate significantly higher infestation frequency in tubeless crinoids. Rather than attach to the anal vent, as is typical for platyceratids, the gastropods that infested tubed crinoids are always found at the tube base and acquired nutrients from their hosts via drilling. It is likely that infesting tubeless crinoids was a more cost effective trophic strategy than drilling tubed crinoids.  相似文献   

2.
A survey was made of 168 specimens of the gastropod mollusk Nucella heyseanafrom 5 samples collected in Amurskii Bay and Vostok Bay (Peter the Great Bay and the Sea of Japan). The variability of Cu, Zn, Cd, Pb, Fe, and Mn contents in gastropod soft tissues was analyzed. The statistic concentrations of the six metals differed significantly among the samples; they were sometimes taken at a distance of a mere several tens of meters apart. N. heyseanacollected near Vladivostok generally had higher concentrations of heavy metals; however, the amount of Zn in the specimens of one sample from the Vostok Bay Reserve was 400 g/g, which is two times greater than that of mollusks from the urbanized zone. The canonical and discriminant analyses and the analysis of the variance indicate that the variation in heavy metal concentration within groups of mollusks (within bays) is comparable in magnitude with the variation among the groups.  相似文献   

3.
4.
  总被引:1,自引:0,他引:1  
The contractile stalks of graptoloid zooids are preserved as organic carbon residues in thecae of the middle Llandovery graptoloid graptolites Rastrites geinitzii and Neolagarograptus? sp. from the Aizpute‐41 core, Latvia. The contractile stalks are surrounded by equant pyrite crystals, resulting in three‐dimensional preservation of the graptolite rhabdosomes, and are associated with sediment of similar composition to, and derived from, the adjacent matrix. Matrix entered the thecae after pyrite crystal growth and filled some of the space left by collapse of the contractile stalks and some intercrystalline cavities; other space is partially infilled by diagenetic minerals. The contractile stalks are parallel‐sided and occupy up to one‐half the metathecal width, which is not inconsistent, assuming post‐mortem shrinkage, with the suggestion that graptoloid zooids filled their thecal tubes in life. The location of the preserved soft tissues, towards the distal ends of the metathecae, is very different from that predicted by decay experiments on the extant pterobranch hemichordate Rhabdopleura; the latter's soft tissues may thus not be a reliable analogue for those of these Silurian graptoloids.  相似文献   

5.
    
  相似文献   

6.
利用顶空取样、溶剂解吸附和气质联用技术分析了黄鼬(Mustela sibirica)肛腺分泌物的挥发性成分。鉴定出的六种化合物均为含硫的环状有机物:(1)2,2-二甲基硫代环丁烷;(2)顺或反2,4-二甲基硫代环丁烷;(3)反-2,3-二甲基硫代环丁烷;(4)2-乙基硫代环丁烷;(5)2-丙基硫代环丁烷;(6)3,3-二甲基-1,2-二硫代环戊烷。尽管黄鼬肛腺成分的组成和鼬鼠其它种存在很大的相似性,但是成分组成的种间差异很明显。另外,2-乙基硫代环丁烷仅存在于雌性黄鼬中。很多研究已经证明对鼠类有驱赶作用的2,2-二甲基硫代环丁烷和2-丙基硫代环丁烷在黄鼬肛腺分泌物同时存在,说明黄鼬肛腺分泌物对鼠类可能有很强的驱避作用。  相似文献   

7.
我们设计了一种用于动物气味的顶空 (headspace)取样装置 ,并结合溶剂解吸附和气质联用技术 ,通过对水貂 (Mustelavision)肛腺分泌物的挥发性成分的分析验证这种装置的可行性。出现 5个气谱峰 ,对应的质谱显示其分子量和分子式依次为峰 1:10 2 (C5H10 S)、峰 2 :10 4(C5H12 S)、峰 3:10 2 (C5H10 S)、峰 4:136(C5H12 S2 )和峰 5 :134 (C5H10 S2 )。峰 1、峰 3和峰 5分别为以前研究所鉴定出的 3种主要成分 :2 ,2 二甲基硫代环丁烷、2 乙基硫代环丁烷和 3,3 二甲基 1,2 二硫代环戊烷 ,2 ,2 二甲基硫代环丁烷为优势成分 ,组成无性别间差异。这些结果与以前研究一致 ,说明了这种顶空取样装置的可靠性。峰 2和峰 4两种成分以前在水貂肛腺中未曾发现 ,初步分析可能分别为 3 甲基 1 丙基硫醇和 1,5 戊二硫醇。尽管这两个成分有待进一步分析确定 ,但可以肯定分子量为 10 4和 136的成分不仅在水貂肛腺分泌物中没有发现过 ,而且在已经研究过的鼬属动物和食肉类的肛腺中都未发现过 ,能检测出更多的成分 ,说明这种方法的可靠性很高。  相似文献   

8.
    
Molecular studies have contributed greatly to our understanding of evolutionary processes that act upon virtually every aspect of living organisms. However, these studies are limited with regard to extinct organisms, particularly those from the Mesozoic because fossils pose unique challenges to molecular workflows, and because prevailing wisdom suggests no endogenous molecular components can persist into deep time. Here, the power and potential of a molecular approach to Mesozoic fossils is discussed. Molecular methods that have been applied to Mesozoic fossils—including iconic, non‐avian dinosaurs— and the challenges inherent in such analyses, are compared and evaluated. Taphonomic processes resulting in the transition of living organisms from the biosphere into the fossil record are reviewed, and the possible effects of taphonomic alteration on downstream analyses that can be problematic for very old material (e.g., molecular modifications, limitations of on comparative databases) are addressed. Molecular studies applied to ancient remains are placed in historical context, and past and current studies are evaluated with respect to producing phylogenetically and/or evolutionarily significant data. Finally, some criteria for assessing the presence of endogenous biomolecules in very ancient fossil remains are suggested as a starting framework for such studies.  相似文献   

9.
A finite element (FE) model is employed to investigate the dynamic response of soft tissues under external excitations, particularly corresponding to the case of harmonic motion imaging. A solid 3D mixed ‘up’ element S8P0 is implemented to capture the near-incompressibility inherent in soft tissues. Two important aspects in structural modelling of these tissues are studied; these are the influence of viscous damping on the dynamic response and, following FE-modelling, a developed state-space formulation that valuates the efficiency of several order reduction methods. It is illustrated that the order of the mathematical model can be significantly reduced, while preserving the accuracy of the observed system dynamics. Thus, the reduced-order state-space representation of soft tissues for general dynamic analysis significantly reduces the computational cost and provides a unitary framework for the ‘forward’ simulation and ‘inverse’ estimation of soft tissues. Moreover, the results suggest that damping in soft-tissue is significant, effectively cancelling the contribution of all but the first few vibration modes.  相似文献   

10.
    
Despite their importance for understanding phylogeny, character evolution and classification, well-constrained homology relationships for posterior plating in crinoids have only recently been attempted. Here, we re-evaluate posterior plate homologies in all major crinoid lineages using development, fossil ontogenies and phylogenetic evidence. Based on these lines of evidence, we change terminology for some posterior plates to correct misnomers and make recommendations for updated terminology of others to better reflect homology. Among pentacrinoids (disparids, hybocrinids, eucladids, flexibles and articulates) the relative position of posterior interray plates, not their topology, reflects homology. From proximal to distal, pentacrinoid posterior plates are the radianal, anal X and right sac plate, regardless of the total number of plates in the adult calyx. Camerate posterior plating contrasts with pentacrinoids, but insufficient data are available to resolve homology relationships between these two clades. More examples of early post-larval ontogeny are needed in camerates and other Palaeozoic crinoids.  相似文献   

11.
    
The specialization of holopodid crinoids to a sessile habit, by directly cementing the cup to a hard substrate and having short arms that interlock on closure to give a watertight seal, led F.A. Bather to speculate in 1928 that they might once have led an intertidal, barnacle‐like existence in shallow water. Although this remains unproven, holopodid‐barnacle associations from the Danian now provide indirect supporting evidence of their similar environmental preferences at that time. It has long been recognized that the holopodid Cyathidium holopus Steenstrup was encrusted by the verrucomorph Verruca prisca ? Bosquet in Danian submarine caves. This crinoid is now known to occur with abundant plates of the brachylepadomorph barnacle Pycnolepas bruennichi Withers in open sea bed settings, suggesting that they lived together on a substrate now lost due to diagenesis. These were most likely to have been azooxanthellate scleractinian corals (benthic; 100+ m estimated water depth) and/or logs (either on sunken benthic islands (100+ m) or floating as pseudoplankton). If the tight, barnacle‐like closure of the holopodid arms was primarily an anti‐predatory adaptation, suggested as an alternative hypothesis, then it was of limited effectiveness and insufficient to prevent the group having to migrate from shallow into deeper water with the stalked crinoids since the Late Cretaceous.  相似文献   

12.
    
Echmatocrinus from the Middle Cambrian Burgess Shale of British Columbia was originally described as the earliest crinoid(?) known from the fossil record. Recently, Conway Morris and Ausich & Babcock have questioned whether Echmatocrinus is in fact an echinoderm, comparing it instead to cnidarians with a polyp-like body and pinnate tentacles, and other authors are beginning to use this reinterpretation. We studied the well-preserved holotype of Echmatocrinus brachiatus, two paratypes, and 18 new specimens recovered from different levels in the Burgess Shale sequence at three localities. All are preserved as pyrite films in dark shale with relatively little relief, suggesting a lightly skeletized body. Complete specimens have a long, slightly tapering, large-plated attachment stalk, a conical cup or calyx with numerous small to medium-sized irregular plates, and 7–10 short arms with heavier plating and (in the holotype) soft appendages alternating from opposite sides of several arms. Several morphologic features indicate that Echmatocrinus is an echinoderm and has crinoid affinities: (1) Sutured plates, shown by darker depressed sutures, slightly raised plate centers, and oriented plate ornament, cover all major parts of the body; (2) reticulate surface ornament in the pyrite film on the plates of all specimens matches the ornament in the Burgess Shale edrioasteroid Walcottidiscus, an undoubted echinoderm, but not the pyritized surfaces of other metazoans in the fauna; (3) this distinctive ornament may represent the surface expression of microporous stereom; (4) possible ligament or muscle pads are present between the arm ossicles to fold and unfurl the more heavily plated arms. Within the echinoderms, only crinoids commonly have a calyx attached by a stalk or stem to the substrate and bear erect, moveable, uniserial arms for feeding. Although Echmatocrinus shows some resemblance to octocorals in overall body shape as an attached suspension feeder, almost all the details are different, indicating that Echmatocrinus is most likely unrelated to this group. All complete specimens of Echmatocrinus are attached to hard substrates, either another fossil or skeletal debris. The new specimens indicate that Echmatocrinus was twice as common (about 0.02%) in the Burgess Shale fauna as previously recorded and represents one of the earliest attached, medium-level, skeletized, suspension feeders or microcarnivores in the fossil record.  相似文献   

13.
    
MANNINGJ. C. & GOLDBLATT, P., 1991. Systematic and phylogenetic significance of the seed coat in the shrubby African Iridaceae, Nivenia, Klattia and Witsenia. The seeds of Nivenia, Klattia and Witsenia, a natural alliance within Nivenioideae, are among their most distinctive features, and seed number and shape constitute at least two synapomorphies for this monophyletic lineage. In this paper we survey the structure of the seed surface of five species of Nivenia and one each of Klattia and Witsenia by scanning electron microsopy (SEM), and study the development of the seed coat in a representative species of each of the three genera. Outgroups for comparison were selected from genera inside and outside the subfamily. The six genera of Nivenioideae are united in having a 3 (– 2) seriate outer integument but the shrubby genera are unique in the family in their tangentially flattened ovules which mature into depressed, flat, scutiform seeds. They display a range of variation in seed coat characters but are specialized in the subfamily and family in having a transparent outer integument. Other genera have pigmented deposits in the outer epidermis of the outer integument. Nivenia and Witsenia are further specialized in having a partially exfoliating outer integument. Klattia is unique among the shrubby genera in having deposits in the second layer of the tegmen, in retaining an intact outer epidermis of the tegmen, and in the fusiform shape of the epidermal cells and striate surface of the seed. Our results are incorporated in a cladogram that expresses our current understanding of the phylogenetic relationships of Nivenioideae.  相似文献   

14.
    
Abstract: A systematic account of highly diverse cyrtocrinid faunules from Upper Jurassic strata of ?tramberk type (Oxfordian–Tithonian) in southern Poland (Polish Carpathians) is presented. Fourteen taxa (Phyllocrinus malbosianus, Ph. stellaris, Ph. sp., Psalidocrinus armatus, Sclerocrinus compressus, Spolonicus sp. nov., Hemicrinus aff. kabanovi, Ancepsicrinus parvus gen. et sp. nov., Tetracrinus baumilleri sp. nov., Eugeniacrinites alexandrowiczi, E. cf. moravicus, E. sp., Eudesicrinus gluchowskii sp. nov. and Hemibrachiocrinus tithonicus sp. nov. are described and illustrated. Representatives of the genus Eudesicrinus, previously recorded only from the Lower Jurassic, are here shown to extend into the uppermost Jurassic. Other cyrtocrinids considered are common in Jurassic/Cretaceous strata across Europe. In the present faunules, isocrinid (Isocrinida), comatulid (Comatulida) and roveacrinid (Roveacrinida sensu Rasmussen, inclusive of Saccocoma) crinoids are associated.  相似文献   

15.
    
In attempts to elucidate the underlying mechanisms of spinal injuries and spinal deformities, several experimental and numerical studies have been conducted to understand the biomechanical behavior of the spine. However, numerical biomechanical studies suffer from uncertainties associated with hard- and soft-tissue anatomies. Currently, these parameters are identified manually on each mesh model prior to simulations. The determination of soft connective tissues on finite element meshes can be a tedious procedure, which limits the number of models used in the numerical studies to a few instances. In order to address these limitations, an image-based method for automatic morphing of soft connective tissues has been proposed. Results showed that the proposed method is capable to accurately determine the spatial locations of predetermined bony landmarks. The present method can be used to automatically generate patient-specific models, which may be helpful in designing studies involving a large number of instances and to understand the mechanical behavior of biomechanical structures across a given population.  相似文献   

16.
Callovian strata in northern Lithuania (Papilė area) have yielded some crinoid taxa[Chariocrinus andreae (Desor),Balanocrinus berchteni HessPugin,B. subteres (Münster inGoldfuss) andIsocrinus nicoleti (Desor)], which have not been described from this area. The only form known previously wasBalanocrinus pentagonalis (Goldfuss).Palaeocomaster jaegeri n. sp. is the first free-living crinoid recorded from the Callovian of eastern Europe. It is characterized by possessing a very low, strongly flattened and narrow radial cavity. A very similar crinoid assemblage is known from the Callovian glacially-derived clays exposed in the Łuków region (eastern Poland), which were originally located near the Baltic Sea during the Middle Jurassic. It is considered that the allochthonous Callovian deposits from Poland are facies equivalents of the deposits known from Lithuania. The sole significant exception is the domination of free-moving comatulids (Comatulida) in the sediments known from the Papilė region, which may suggest that the Lithuanian sea basin was a little shallower than that located farther west in the Baltic area.   相似文献   

17.
Pelvic prolapse affects one woman in three of all ages combined and is quite common for more than 60% of patients over 60 years of age. The treatment of this pathological problem is one of the biggest challenges to the gynaecologist today. The rate of surgical intervention failure is quite significant. The recurrence of prolapse could be related to inadequate surgical technique or the pathology or/and biomechanical deficiency of the soft tissues. The modelling and simulation of the behaviour of the pelvic cavity could be a major tool for specific evaluation of pelvic status. A first stage of this model is being developed and reported. The computer-aided design model of the organs of the pelvic floor is created using magnetic resonance image data and the ligament boundary conditions are defined. A multi-organ geometric model is thus created and studied.  相似文献   

18.
    
Modelling transversely isotropic materials in finite strain problems is a complex task in biomechanics, and is usually addressed by using finite element (FE) simulations. The standard method developed to account for the quasi-incompressible nature of soft tissues is to decompose the strain energy function (SEF) into volumetric and deviatoric parts. However, this decomposition is only valid for fully incompressible materials, and its use for slightly compressible materials yields an unphysical response during the simulation of hydrostatic tension/compression of a transversely isotropic material. This paper presents the FE implementation as subroutines of a new volumetric model solving this deficiency in two FE codes: Abaqus and FEBio. This model also has the specificity of restoring the compatibility with small strain theory. The stress and elasticity tensors are first derived for a general SEF. This is followed by a successful convergence check using a particular SEF and a suite of single-element tests showing that this new model does not only correct the hydrostatic deficiency but may also affect stresses during shear tests (Poynting effect) and lateral stretches during uniaxial tests (Poisson's effect). These FE subroutines have numerous applications including the modelling of tendons, ligaments, heart tissue, etc. The biomechanics community should be aware of specificities of the standard model, and the new model should be used when accurate FE results are desired in the case of compressible materials.  相似文献   

19.
20.
    
An important function of song production by male crickets is to attract conspecific females. These sound signals can be used to infer species boundaries as they can provide indirect evidence for reproductive isolation. However, many studies of orthopteran diversity in South-east Asia are based mainly on morphology and only occasionally acoustics. As such, there is a lack of information on how acoustic data can be congruent with morphological data when used to delineate species. Crickets of the genus Gymnogryllus (Grylloidea, Gryllidae), are such an example. Gymnogryllus are relatively speciose, but their calling songs have not been studied. We collected specimens and calling songs of five Gymnogryllus species from South-east Asia. The acoustic parameters of the calls, along with male tegminal venation and morphology genitalia, were compared. All data types showed congruency in distinguishing G. sylvestris and G. leucostictus from each other and from the other species. Inferring species boundaries for G. angustus, G. malayanus, and G. unexpectus using acoustics and tegminal morphometry proves to be more challenging. While acoustics, tegminal morphometry, and genital morphology are likely to be useful for inferring species of Gymnogryllus from different species groups, greater coverage of taxa is needed to resolve taxonomy of closely related Gymnogryllus.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号