贵州剑河寒武系“清虚洞组”管状微体骨骼化石初步研究

华南寒武系地层中广泛富集微体骨骼化石,为解决某些疑难化石的亲缘关系及研究早期后生动物的演化提供了重要化石证据。在贵州剑河八郎"清虚洞组"中发现一些管状微体骨骼化石。经鉴定后主要有4属,分别为小钻孔螺Torellella、似软舌螺Hyolithellus、鞘状螺Coleoloides和表面具鳞片状管状化石Mongolitubulus squamifer。Mongolitubulus分布范围较为广泛,本文结合前人对该化石亲缘关系的探讨及剑河寒武系"清虚洞组"化石的特征,推测M.squamifer可能是高肌虫的装饰刺。     

Lizards as a plant's 'hired help': letting pollinators in and seeds out

It is well-known that plants utilize many different kinds of animals for pollination and dispersal of their seeds, but an alternative kind of evolutionary relationship has attracted less attention: animals can facilitate pollen and seed transport without acting as a vector. We studied interactions between an epacridaceous plant (the honey bush, Richea scoparid) and a lizard (the snow skink, .Niveoscincus microtepidotus) near the summit of Mount Wellington, Tasmania. The lizards gain access to the plant's nectar by tearing the fused petals (the calyptra) from the flower, thus exposing the plant's reproductive organs. Snow skinks forage selectively on flowers with higher-than-average nectar content, suggesting that this behaviour has evolved in response to plant characteristics. Lizard foraging may benefit R. scoparia , because calyptra remain attached unless a lizard tears the flower open. Our experiments demonstrated that the lizard's calyptra removal dramatically increased the plant's seed release. In 60 fruits from flowers with their calyptra intact, no seeds at all were released. However, 57 out of 60 (87%) fruits from flowers with their calyptra removed by the lizards successfully released their seeds. This system appears to involve reciprocal evolutionary changes in the interacting species (behaviour in the lizards and reproductive morphology in the plant). Thus the system seems to provide an unusual case of coevolution.     

陕南早寒武世早期水螅营养体及管状疑难化石

陕南宁强宽川铺生物群发现具触手的水螅营养体化石,同层位同时发现大量磷质管状疑难化石,其管体上可分辨出可能的出芽特征,推测该类具出芽特征管体可能和现代群体生活的薮枝螅(Obelia)有关。     

Structural, physiological, and stable carbon isotopic evidence that the enigmatic Paleozoic fossil Prototaxites formed from rolled liverwort mats

New structural, nutritional, and stable carbon isotope data may resolve a long-standing mystery-the biological affinities of the fossil Prototaxites, the largest organism on land during the Late Silurian to Late Devonian (420-370 Ma). The tree trunk-shaped specimens, of varying dimensions but consistent tubular anatomy, first formed prior to vascular plant dominance. Hence, Prototaxites has been proposed to represent giant algae, fungi, or lichens, despite incompatible biochemical and anatomical observations. Our comparative analyses instead indicate that Prototaxites formed from partially degraded, wind-, gravity-, or water-rolled mats of mixotrophic liverworts having fungal and cyanobacterial associates, much like the modern liverwort genus Marchantia. We propose that the fossil body is largely derived from abundant, highly degradation-resistant, tubular rhizoids of marchantioid liverworts, intermixed with tubular microbial elements. Our concept explains previously puzzling fossil features and is consistent with evidence for liverworts and microbial associates in Ordovician-Devonian deposits, extensive ancient and modern marchantioid mats, and modern associations of liverworts with cyanobacteria and diverse types of fungi. Our interpretation indicates that liverworts were important components of Devonian ecosystems, that some macrofossils and microfossils previously attributed to "nematophytes" actually represent remains of ancient liverworts, and that mixotrophy and microbial associations were features of early land plants.     

Phylogeography of five Polytrichum species within Europe

Using allozymes and microsatellites we have analysed the genetic structure among European populations for several Polytrichum species to infer relevant factors, such as historical events or gene flow, that have shaped their genetic structure. As we observed low levels of genetic differentiation among populations, and no decreasing levels of genetic variation with increasing latitude within most of the examined species, no genetic evidence was obtained for a step-wise recolonization of Europe from southern refugia after the latest glacial period for P. commune , P. uliginosum , P. formosum and P. piliferum . The near absence of population substructuring within these species does indicate that extensive spore dispersal is the most important factor determining the genetic structure among European Polytrichum populations. Gene flow levels have apparently been sufficient to prevent genetic differentiation among populations caused by genetic drift, and to wipe out any genetic structure caused by the postglacial recolonization process. On the other hand, increased genetic differentiation of alpine P. formosum populations suggests that mountain ranges might restrict gene flow significantly among Polytrichum populations. In contrast to most examined Polytrichum species, P. juniperinum showed high levels of genetic differentiation and a profound genetic structure. Assuming that gene flow is not more restricted in P. juniperinum , these findings suggest that this species has recolonized Europe after the latest glacial period from two different refugia, one possibly being the British Isles.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society 2003, 78, 203–213.     

Mineralisation of filamentous cyanobacteria in Lake Thetis stromatolites,Western Australia

Stromatolites are cited as some of the earliest evidence for life on Earth, but problems remain in reconciling the paucity of microfossils in ancient carbonate examples with the abundance of microbes that help construct modern analogues. Here, we trace the mineralisation pathway of filamentous cyanobacteria within stromatolites from Lake Thetis, Western Australia, providing new insights into microfossil preservation in carbonate stromatolites. Lake Thetis cyanobacteria exhibit a spectrum of mineralisation processes that include early precipitation of Mg‐silicates, largely controlled by the morphochemical features of the cyanobacteria, followed by aragonite formation that is inferred to be driven by heterotrophic activity. Fossilised cyanobacteria with high‐quality morphological preservation are characterised by a significant volume of authigenic Mg‐silicates, which have preferentially nucleated in/on extracellular organic material and on cell walls, and now replicate the region once occupied by the cyanobacterial sheath. In such specimens, aragonite is restricted to the outer sheath margin and parts of the cell interior. Cyanobacteria that display more significant degradation appear to possess a higher ratio of aragonite to Mg‐silicate. In these specimens, aragonite forms micronodules in the sheath zone and is spatially associated with the inferred remains of heterotrophic bacteria. Aragonite also occurs as an advancing front from the outer margin of the sheath where it is commonly intergrown with Mg‐silicates. Where there is no evidence of Mg‐silicates within filaments, the fidelity of microfossil preservation is poor. In these cases, individual filaments may no longer be visible under light microscopy, and little organic material remains, but filament traces remain detectable using electron microscopy due to variations in aragonite texture. These data provide further evidence that authigenic silicate minerals play a crucial role in the fossilisation of micro‐organisms; in their absence, carbonate crystal growth potentially mediated by heterotrophic microbial decay may largely obliterate morphological evidence for life within stromatolites, although mineralogical traces may still be detectable using electron microscopy.     

The cuticle on the gametophyte calyptra matures before the sporophyte cuticle in the moss Funaria hygrometrica (Funariaceae)

? Premise of the study: In vascular plants, leaf primordia prevent desiccation of the shoot apical meristem. Lacking leaves, the undifferentiated moss sporophyte apex is covered by the calyptra, a cap of maternal gametophyte tissue that is hypothesized to function in desiccation protection. Herein, we compare cuticle development on the calyptra and sporophyte to assess the calyptra's potential to protect the sporophyte from desiccation. As the first comprehensive study of moss sporophyte cuticle development, this research broadens our perspectives on cuticle development and evolution across embryophytes. ? Methods: Calyptrae and sporophytes at nine developmental stages were collected from a laboratory-grown population of the moss Funaria hygrometrica. Tissues were embedded, sectioned, then examined using transmission electron microscopy. Epidermal cells were measured for thickness of the cuticle layers, cell wall thickness, and lumen size. ? Key results: The calyptra cuticle develops precociously and reaches maturity before the sporophyte cuticle. Calyptrae are covered by a four-layered cuticle at all stages, whereas sporophyte cuticle maturation is delayed until sporangium formation. The development and thickening of the sporophyte cuticle occurs in an acropetal wave. ? Conclusions: A multilayered calyptra cuticle at the earliest developmental stages is consistent with its ability to protect the immature sporophyte from desiccation. Young sporophytes lack a complex cuticle and thus may require protection, whereas in older sporophytes a mature cuticle develops. The moss calyptra is not a vestigial structure, but rather the calyptra's role in preventing desiccation offers a functional explanation for calyptra retention during the 450 Myr of moss evolution.     

Evidence for a lacustrine faunal refuge in the Larsemann Hills, East Antarctica, during the Last Glacial Maximum

Aim  There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c . 130,000 yr bp , i.e. prior to the LGM.
Location  Lake Reid, Larsemann Hills, East Antarctica (76°23' E; 69°23' S).
Methods  Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c . 130,000 yr bp .
Results  Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM.
Main conclusion  The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent.     

北京延庆地区雾迷山组燧石相微体古生物研究

本文报道的微体化石产于北京延庆地区雾迷山组中的燧石相岩层中,共鉴定出10个属19个种,其中含1个新种,3个未定种,以及2个相似种。化石类型以蓝细菌中的颤藻科、念珠藻科和色球藻科属种为主,还保存有少量绿藻和大量分类位置未定的藻类。新的化石资料必将进一步丰富燕山雾迷山组的微化石群的内容,并为进一步评价雾迷山组微化石的生物演化和多样性的水平,及其生物地层意义提供更充分的依据。     

Garnet-filled trails associated with carbonaceous matter mimicking microbial filaments in Archean basalt

The study of the earliest traces of life on Earth can be complicated by abiotically formed biomorphs. We report here the finding of clustered micrometer-sized filaments of iron- and calcium-rich garnets associated with carbonaceous matter in an agate amygdale from a 2.7-billion-year-old basalt of the Maddina Formation, Western Australia. The distribution of carbonaceous matter and the mineral phases composing the filaments were analyzed using a combination of confocal laser scanning microscopy, laser-Raman micro-spectroscopy, focused ion beam sectioning and transmission electron microscopy. The results allow consideration of possible biogenic and abiotic processes that produced the filamentous structures. The filaments have a range of sizes, morphologies and distributions similar to those of certain modern iron-mineralized filamentous bacteria and some ancient filamentous structures interpreted as microfossils. They also share a high morphological similarity with tubular structures produced by microbial boring activity. However, the microstructures and the distribution of carbonaceous matter are more suggestive of an abiotic origin for the filaments. They are characteristic features of trails produced by the displacement of inclusions associated with local dissolution of their silica matrix. Organic compounds found in kerogen or bitumen inclusions may have contributed significantly to the dissolution of the quartz (or silica gel) matrix driving filamentous growth. Discriminating the products of such abiotic organic-mediated processes from filamentous microfossils or microbial borings is important to the interpretation of the scarce Precambrian fossil record and requires investigation down to the nanoscale.     

浅议峡东陡山沱组的“瓶状微化石”

通过对峡东晚震旦世陡山沱组岩石样品的化学浸解处理、连续切片研究及大量薄片观察,作者认为先前报道的陡山沱组“瓶状微化石”,即所谓最古老的原生动物的外壳遗骸,实际上并非什么瓶状微化石,而是一种有蓝藻（可能还有细菌）参与的沉积构造。     

A phylogenetic circumscription of Polytrichastrum (Polytrichaceae): Reassessment of sporophyte morphology supports molecular phylogeny

Mosses arguably possess the most structurally complex sporangia of any extant land plants, a consequence of being the monosporangiophyte lineage most strongly adapted to terrestrial environments. Morphological and functional variation in the mechanisms that regulate spore release in one of the major classes of mosses, the Polytrichopsida, is largely unexplored, while recent research indicates that the most distinctive structure, the peristome, has evolved independently in the Polytrichopsida and in other mosses. The genus Polytrichastrum was separated from Polytrichum on the basis of such sporangial characters, although the critical features had until recently only been examined using light microscopy, and strong evidence from molecular data indicated that Polytrichastrum as currently circumscribed is polyphyletic. Here we use Bayesian ancestral character state reconstruction in conjunction with extensive scanning electron micrographic studies to elucidate probable morphology at ancestral nodes and define natural taxa. As well as clarifying the structure, evolution, and aspects of development of the peristome-epiphragm complex in this highly prominent group of mosses, the results provide a basis for a revised phylogenetic taxonomy in which the species of Polytrichastrum sect. Aporotheca are recognized once more within Polytrichum.     

A hundred-year-old question: is the moss calyptra covered by a cuticle? A case study of Funaria hygrometrica

Background and Aims

The maternal gametophytic calyptra is critical for moss sporophyte development and ultimately sporogenesis. The calyptra has been predicted to protect the sporophyte apex, including the undifferentiated sporogenous region and seta meristem, from desiccation. We investigate the hypothesis that this waterproofing ability is due to a waxy cuticle. The idea that moss calyptrae are covered by a cuticle has been present in the literature for over a century, but, until now, neither the presence nor the absence of a cuticle has been documented for any calyptra.

Methods

The epidermis of the calyptra, leafy gametophyte and sporophyte sporangia of the moss Funaria hygrometrica were examined using scanning and transmission electron microscopy. Thicknesses of individual cuticle layers were quantified and compared statistically. The immunochemistry antibody (LM19) specific for pectins was used to locate cell wall material within the cuticle.

Key Results

A multi-layered cuticle is present on the calyptra of F. hygrometrica, including layers analogous to the cuticular layer, cell wall projections, electron-lucent and electron-dense cuticle proper observed in vascular plants. The calyptra rostrum has a cuticle that is significantly thicker than the other tissues examined and differs by specialized thickenings of the cuticular layer (cuticular pegs) at the regions of the anticlinal cell walls. This is the first documentation of cuticular pegs in a moss.

Conclusions

The calyptra and its associated cuticle represent a unique form of maternal care in embryophytes. This organ has the potential to play a critical role in preventing desiccation of immature sporophytes and thereby may have been essential for the evolution of the moss sporophyte.     

Early evolution of large micro‐organisms with cytological complexity revealed by microanalyses of 3.4 Ga organic‐walled microfossils

The Strelley Pool Formation (SPF) is widely distributed in the East Pilbara Terrane (EPT) of the Pilbara Craton, Western Australia, and represents a Paleoarchean shallow‐water to subaerial environment. It was deposited ~3.4 billion years ago and displays well‐documented carbonate stromatolites. Diverse putative microfossils (SPF microfossils) were recently reported from several localities in the East Strelley, Panorama, Warralong, and Goldsworthy greenstone belts. Thus, the SPF provides unparalleled opportunities to gain insights into a shallow‐water to subaerial ecosystem on the early Earth. Our new micro‐ to nanoscale ultrastructural and microchemical studies of the SPF microfossils show that large (20–70 μm) lenticular organic‐walled flanged microfossils retain their structural integrity, morphology, and chain‐like arrangements after acid (HF‐HCl) extraction (palynology). Scanning and transmitted electron microscopy of extracted microfossils revealed that the central lenticular body is either alveolar or hollow, and the wall is continuous with the surrounding smooth to reticulated discoidal flange. These features demonstrate the evolution of large micro‐organisms able to form an acid‐resistant recalcitrant envelope or cell wall with complex morphology and to form colonial chains in the Paleoarchean era. This study provides evidence of the evolution of very early and remarkable biological innovations, well before the presumed late emergence of complex cells.     

Carbohydrate and lipid levels in two Polytrichum moss species growing on the Alaskan tundra

Two tundra Polytrichum moss species were sampled in the field near Barrow, Alaska, three times during the growing season. Lipid, sugar, and starch concentrations of the green above ground shoots and below ground rhizomes were analyzed. Lipid and TNC (sugar + starch) concentrations were higher in Polytrichum commune growing on raised polygon rims than in Polytrichum alpinum. There were no significant differences between the two populations of P. alpinum. Green parts had significantly higher lipid concentrations than rhizomes in P. commune but not in P. alpinum. Both species had significantly higher sugar concentration in green shoots and higher starch concentrations in the rhizome and sugar concentration varied significantly in both species. Seasonal variation of TNC concentration levels were significant only in P. commune. A statistically significant positive relationship was found between lipid and TNC concentration while a stronger statistically significant negative relationship was found between sugar and starch concentration. The first is interpreted as an adaptation to drought in surface waxes and osmoticum while the second is interpreted as conversion indicator depending on tissue and use. Polytrichum mosses resemble evergreen vascular plants in their seasonal stability of these compound groups.     

华北高于庄组硅化微体化石组合的古环境

华北中元古代高于庄组 ( 1 4- 1 5亿年 )的硅质叠层石中保存了完好的多种微生物化石。从这些叠层石的微细构造分析 ,成岩早期硅质矿物的交代作用为微体化石的原位保存起了很重要的作用。除部分居住者和浮游的分子外 ,两种丝状蓝藻 ( Siphonophycus inornatum和Eoschizothric composita)和两种球状蓝藻 ( Coccostratusdispergens和 Eoentophysalisbelcherensis)是这些藻席的主要建造者。以球状蓝藻 Eoentophysalis为主的藻席可能发育于潮下高能环境中 ;而以多种丝状蓝藻为主的藻席可能反映了当时的沉积环境为中—高潮间带的局部静止小水体     

中国湖北秭归县庙河村早寒武世天竺山段的硅化微体化石

描述了湖北秭归县庙河村寒武系最底部(天竺山段)硅化微体化石13属16种,并论述了其地层意义.所有微体化石皆见于燧石切片中,此组合含大量小个体的具刺凝源类,以Micrhystridium ampliatum Wang为主,并与Paracymatiosphaera spp.,其它球形分子Lelosphaeridia,Favososphaeridium,Eoaperturilites及丝状体Obruchevella 和Megathrix共生,此地真正的陡山沱组是以含大量的和形态复杂的疑源类及简单的丝状体和球状化石为特征,这两个可靠的微体化石组合的发现和区分对本区及邻区震旦系-寒武系过渡层的划分和地层对比有重要意义.     

从微体化石群看我国沿海早第三纪含油盆地的差异

对我国沿海3个含油盆地－珠江口、北部湾和渤海湾盆地下第三系湖相生油岩中的微体化石群进行比较分析。3个盆地中以渤海湾盆地下第三系湖相化石群最为丰富,数量多,分异度高,而且化石群以地方性属种比例高、咸水类型多,存在“海源陆生生物化石”为特征;北部湾盆地,在涠洲组和流沙港组发现较多的介形类化石及个别腹足类和轮藻化石;而珠江口下经三系湖相地层中,微体化石罕见,只在个别层位发现贝壳碎片。据化石群特征,推测渤海湾盆地早第三纪是封闭型的咸水湖泊,而且部分沉积时期,可能是以Cl^-和Na^ 为主的咸水湖泊;珠江口盆地早第三纪是湖水矿化度低、硬度、pH值也低的淡水湖泊;而北部湾盆地早第三纪可能仍属淡水湖泊,但有一定的矿化度。     

Microfossils from the middle Precambrian McArthur Group,Northern Territory,Australia

Microfossils have been detected in several formations of the McArthur Group (about 1600 m.y. old), in petrological thin sections and in macerations. Some of these occur associated with a lead-zinc ore body; others have been found in well-preserved dolomites and cherts. The variety of microfossils observed is considerable, and their state of preservation is good. Large numbers of singlecelled, colonial and multicellular organisms occur; in the latter, at least one clear case of cell differentiation can be demonstrated. Some of the organisms are morphologically comparable with blue-green algae such as the Chroococaceae, but, unlike the well-known Bitter Springs microflora, the assemblage is notably poor in filamentous algae. The filaments that do occur are not septate, and may represent discarded blue-green algal sheaths. Many of the microorganisms are extremely small in size, and in some cases, colonial structures composed of large numbers of 1 m diameter cells are present, that may represent bacterial remains. Most of the microfossils occur in stromatolitic cherts, but the lead-zinc orebody from which some were obtained is a fine-grained dolomitic shale.Stratigraphically, this new assemblage occurs in sediments of age intermediate between the well-known Gunflint Chert assemblage and the equally well-known Bitter Springs flora. The level of organization of the microfossils represents a great advance on the of the Gunflint Chert microfossils, in that demonstrably colonial and large multicellular microorganisms occur, as well as cells of a relatively large size. No convincing evidence for the presence of nuclei or nuclear membranes has yet been found in McArthur Group microorganisms, but the large size and organizational complexity of some of the structures suggests that the origin of the eukaryotic cell may occur rather earlier in geologic times than previous indications have suggested.     

Evidence for plant viruses in the region of Argentina Islands, Antarctica

This work focused on the assessment of plant virus occurrence among primitive and higher plants in the Antarctic region. Sampling occurred during two seasons (2004/5 and 2005/6) at the Ukrainian Antarctic Station 'Academician Vernadskiy' positioned on Argentina Islands. Collected plant samples of four moss genera (Polytrichum, Plagiatecium, Sanionia and Barbilophozia) and one higher monocot plant species, Deschampsia antarctica, were further subjected to enzyme-linked immunosorbent assay to test for the presence of common plant viruses. Surprisingly, samples of Barbilophozia and Polytrichum mosses were found to contain antigens of viruses from the genus Tobamovirus, Tobacco mosaic virus and Cucumber green mottle mosaic virus, which normally parasitize angiosperms. By contrast, samples of the monocot Deschampsia antarctica were positive for viruses typically infecting dicots: Cucumber green mottle mosaic virus, Cucumber mosaic virus and Tomato spotted wilt virus. Serological data for Deschampsia antarctica were supported in part by transmission electron microscopy observations and bioassay results. The results demonstrate comparatively high diversity of plant viruses detected in Antarctica; the results also raise questions of virus specificity and host susceptibility, as the detected viruses normally infect dicotyledonous plants. However, the means of plant virus emergence in the region remain elusive and are discussed.