寒武系小碳化石(SCFs)的研究进展及意义

所谓SCFs(Small Carbonaceous Fossils),可译为"小碳化石",其大小跨越了传统的微观与宏观界线(以肉眼可见与否为标准),是一个特定化石群体的统称。它的实质含义,是指通过氢氟酸(HF)等无机酸浸泡泥岩/页岩样品后经过滤、浓缩而获得的一类体积微小的有机碳质薄膜化石,包括后生动物残片、丝状藻/菌类碎片、疑源类等类型。在小碳化石概念被正式提出之前,国外学者曾先后用有机质壁微体化石(Organic-walled microfossils)、碳质微体化石(Carbonaceous microfossils)与布尔吉斯页岩型微体化石(Burgess Shale-type microfossils)来表述此类化石。目前在国际上,与布尔吉斯页岩型(BST)化石库和奥斯坦(Orsten)型化石库一样,小碳化石已经成为寒武纪古生物学及生物埋藏学等领域研究的一个重要的新窗口;同时,通过三类特异埋藏化石的对比研究,实现优势互补,从而能够更好地阐述早期生物的演化与多样性。     

Spirodesmos milanai n. isp.: A Shallow-Water Spiral Trace Fossil from the Cambrian of the Eastern Cordillera,Northwest Argentina

Abstract

A new ichnofossiliferous locality in Salta Province (northwest Argentina) contains an association with numerous irregular spiral traces assigned to Spirodesmos milanai n. isp., in mature sandstones and quartzites with rippled bedding surfaces, rare wavy lamination and cross-bedded stratification. This record of early spiral behavior is interpreted as a primitive grazing method formed on muddy laminae above sand layers, and is related to a feeding strategy of an annelid-type of organism. Associated traces are Cruziana cf. semiplicata, Diplocraterion isp., Monocraterion isp., Rusophycus isp., Skolithos linearis Haldeman and Skolithos magnus Howell. The ichnoassemblage is similar to a shallow-water ichnoassociation from the Permian Ecca Group of South Africa (Mason et al., 1983 Mason, T. R., Stanistreet, I. G. and Tavener-Smith, R. 1983. Spiral trace fossils from the Permian Ecca Group of Zululand. Lethaia, 16: 241–247. [Crossref], [Web of Science ®] , [Google Scholar]).     

云南早寒武世澄江化石库中两种埋藏相的化石定量分析

通过昆明海口马房村同一个采坑的化石连续采集和统计,对澄江化石库中两种埋藏相(以事件层泥岩和背景层泥岩所代表)内化石保存和组合特征进行定量研究,结果表明:(1)事件层内化石量并不随单一事件层厚度变化而变化。物种在剖面上不同层位的事件层内分布不均匀,表现为单层富集现象;而背景层内的化石含量与背景层的沉积厚度有关,背景层的沉积厚度越厚,化石数量就越多。(2)事件层与背景层内化石组合和结构存在很大差异。事件层内化石组合与背景层内化石组合相比具有更多的物种组成和更复杂的古群落结构;而背景层内化石组合面貌单调,在剖面上保持稳定。(3)事件层内化石生物体腐烂发生在埋藏之后,绝大多数化石生物是被活埋后保存下来的;而背景层内化石主要表现为外壳和弱矿化有机质生物表皮在海床表面长时间停滞而堆积形成,明显受到时间均衡作用(time-average)的影响。(4)事件层内化石在埋藏前无搬运作用,或发生近原栖息地的快速搬运,埋藏后无生物扰动。背景层内大量壳体相连的双瓣壳节肢动物化石和完整海绵体化石的存在则表明,背景层代表一个低氧、低能并具有有限生物扰动的沉积环境。     

西伯利亚地台早寒武世钙藻的发育特征

西伯利亚地台的新元古代到早寒武世间的钙藻化石特别丰富,为研究钙藻化石的发育历史提供了模式。在几次演化事件背景下记录了演化的两次转折,其中一个是藻类的普遍钙化,还有一个是Botomian晚期到Toyonian早期之间在西伯利亚地台缺失钙藻化石记录,而在其它地区包括西伯利亚地台的边缘(Altay—Sayan地区),钙藻的丰度却达到了最大。     

葫芦虫化石在寒武纪关山生物群中的发现及其意义

报道产自昆明高楼房的寒武纪早期关山生物群中的葫芦虫化石,这是该类动物在全球的第三例化石记录。葫芦虫化石在关山生物群的发现对了解该类动物以及寒武纪动物群生态和演化等均有着重要意义。     

磷酸盐化球状化石研究述评

磷酸盐化球状化石是近 2 0年来才相继发现的一类微体化石 ,主要产于下寒武统梅树村阶和震旦系陡山沱组的含磷地层。研究初期其生物亲缘就存在动植物之争 ,但多数专家将其作为分类位置未定的球状化石。近年来 ,由于一些学者研究发现部分磷酸盐化球状化石具有后生动物胚胎发育序列的特征 ,认为它们可能是刺细胞动物或两侧对称动物的胚胎化石 ,从而引起了国内外众多学者 ,尤其是藻类和疑源类专家的关注和热烈讨论。本文在总结球状化石研究进程的基础上 ,对其当前的研究焦点 ,如归属问题、后生动物胚胎化石、保存机制及分类命名 ,进行了简略的评述 ;同时 ,简要介绍了其研究意义。     

A new trace fossil from the Middle Cambrian of the Grand Canyon, Arizona, USA

An unusual trace fossil from the Middle Cambrian Bright Angel Shale Formation of the Grand Canyon, Arizona, consisting of two rows of biserially opposed circular or oval depressions, with alternating symmetry, is described as Bicavichnites martini ichnogen. et ichnosp. nov. While specimens of this trace may represent the surface expression of a complex treptichnid-like burrow system, it is more likely that they are the walking traces of a bilaterally symmetrical benthic animal. The large variation in external width within the trackways is inconsistent with an arthropod producer. The trackway morphology and presence of limb spur marks suggest that the trace maker may have been a lobopodian, a Cambrian relative of modern onychophorans.     

球形小壳化石在贵州金沙寒武系牛蹄塘组的首次发现

贵州金沙岩孔剖面的寒武系牛蹄塘组为跨阶地层,以镍钼矿层为分界面,其上部属于筇竹寺阶,下部为梅树村阶。近期,作者利用15%左右的醋酸浸泡金沙岩孔剖面牛蹄塘组底部(梅树村阶)的岩样,发现了以球形化石为主的单胞、多胞球形类小壳动物化石,包括Olivooides pearformis和其余两类未确定的球形化石。此次球形化石的发现不仅丰富了牛蹄塘生物群的生物面貌,而且为解译早期后生动物的起源和演化、胚胎生物学提供了化石资料。     

A New Frontier for Palaeobiology: Earth's Vast Deep Biosphere

Diverse micro‐organisms populate a global deep biosphere hosted by rocks and sediments beneath land and sea, containing more biomass than any other biome except forests. This paper reviews an emerging palaeobiological archive of these dark habitats: microfossils preserved in ancient pores and fractures in the crust. This archive, seemingly dominated by mineralized filaments (although rods and coccoids are also reported), is presently far too sparsely sampled and poorly understood to reveal trends in the abundance, distribution, or diversity of deep life through time. New research is called for to establish the nature and extent of the fossil record of Earth's deep biosphere by combining systematic exploration, rigorous microanalysis, and experimental studies of both microbial preservation and the formation of abiotic pseudofossils within the crust. It is concluded that the fossil record of Earth's largest microbial habitat may still have much to tell us about the history of life, the evolution of biogeochemical cycles, and the search for life on Mars.     

DEVELOPMENT AND DIVERSIFICATION OF TRUNK PLATES OF THE LOWER CAMBRIAN LOBOPODIANS

Abstract:  Isolated lobopodian plates are reported from Early Cambrian strata at five localities in southern China. A wide variety of morphologies is represented, reflecting a considerable diversification within the phylum at this time. The new taxon Microdictyon jinshaense is erected and new observations are recorded on established taxa, based on examination of more than 600 well-preserved plates; irregular patterns of node distribution and the presence of large spines are documented on some taxa for the first time. Rare specimens in which two plates are conjoined, with a larger plate underlying a smaller one, are interpreted as showing a new sclerite emerging underneath its predecessor, which has not yet been moulted. These specimens confirm the process of ecdysis in the lobopodians and contribute to a fuller understanding of the ontogeny of these organisms. A functional hypothesis that suggests that the plates were complex visual structures is refuted; it is possible that they were sites of muscle attachment, but a protective role is regarded as more plausible.     

Infaunal augurs of the Cambrian explosion: An Ediacaran trace fossil assemblage from Nevada,USA

Morphologically complex trace fossils, recording the infaunal activities of bilaterian animals, are common in Phanerozoic successions but rare in the Ediacaran fossil record. Here, we describe a trace fossil assemblage from the lower Dunfee Member of the Deep Spring Formation at Mount Dunfee (Nevada, USA), over 500 m below the Ediacaran–Cambrian boundary. Although millimetric in scale and largely not fabric‐disruptive, the Dunfee assemblage includes complex and sediment‐penetrative trace fossil morphologies that are characteristic of Cambrian deposits. The Dunfee assemblage records one of the oldest documented instances of sediment‐penetrative infaunalization, corroborating previous molecular, ichnologic, and paleoecological data suggesting that crown‐group bilaterians and bilaterian‐style ecologies were present in late Ediacaran shallow marine ecosystems. Moreover, Dunfee trace fossils co‐occur with classic upper Ediacaran tubular body fossils in multiple horizons, indicating that Ediacaran infauna and epifauna coexisted and likely formed stable ecosystems.     

辽河断陷东部晚寒武世至早奥陶世牙形石物地层

根据王参1井和界3井所产的牙形石动物群的分析,讨论了辽河断陷东部存在晚寒武世长山组;早奥陶世下马家沟组和冶里组的地层,与国内外有关的地区进行了对比,同时,以实例说明了仅仅根据岩性和电性划分出的晚寒武世凤山组、崮山组,中寒武世张夏组以及早奥陶世上马家沟组、亮甲山组层尚需进一步的系统的牙形石生物地层工作来核实或修正。     

记比耶鱼(Birgeria)在中国的首次发现

记述了采自云南罗平晚三叠世法郎组竹杆坡段的比耶鱼一新种──刘氏比耶鱼（Ｂｉｒｇｅｒｉａ ｌｉｕｉ ｓｐ． ｎｏｖ．）,这是比耶鱼化石在中国的首次发现。刘氏比耶鱼与产自瑞士圣乔治山中三叠世边境沥青层的史氏比耶鱼最为相近,两者仅在尾柄长高之比、尾鳍长短与上下叶外缘交角、背鳍和臀鳍辐状支鳍骨的数目、臀鳍辐状骨骨板的大小、以及侧线管骨化与否等特征上略有差异。比耶鱼与软骨硬鳞鱼超目的鲟形目最为接近,两者共有一系列特征,如除尾上叶外体侧裸露,副蝶骨末端伸达头后,鳃盖骨退化;但比耶鱼同时也具有不少的特有特征,代表了软骨硬鳞鱼超目的另一类群──比耶鱼目（Ｂｉｒｇｅｒｉｉｆｏｒｍｅｓ　ｏｒｄ． ｎｏｖ．）。刘氏比耶鱼的发现进一步表明华南扬子区中、晚三叠世鱼类化石与特提斯西部的鱼群具有密切的动物地理关系。     

Experimental taphonomy of Artemia reveals the role of endogenous microbes in mediating decay and fossilization

Exceptionally preserved fossils provide major insights into the evolutionary history of life. Microbial activity is thought to play a pivotal role in both the decay of organisms and the preservation of soft tissue in the fossil record, though this has been the subject of very little experimental investigation. To remedy this, we undertook an experimental study of the decay of the brine shrimp Artemia, examining the roles of autolysis, microbial activity, oxygen diffusion and reducing conditions. Our findings indicate that endogenous gut bacteria are the main factor controlling decay. Following gut wall rupture, but prior to cuticle failure, gut-derived microbes spread into the body cavity, consuming tissues and forming biofilms capable of mediating authigenic mineralization, that pseudomorph tissues and structures such as limbs and the haemocoel. These observations explain patterns observed in exceptionally preserved fossil arthropods. For example, guts are preserved relatively frequently, while preservation of other internal anatomy is rare. They also suggest that gut-derived microbes play a key role in the preservation of internal anatomy and that differential preservation between exceptional deposits might be because of factors that control autolysis and microbial activity. The findings also suggest that the evolution of a through gut and its bacterial microflora increased the potential for exceptional fossil preservation in bilaterians, providing one explanation for the extreme rarity of internal preservation in those animals that lack a through gut.     

辽河断陷盆地西部晚寒武世至早奥陶世牙形石生物地层

辽河断陷盆地西部凹陷古潜山顶部地层的时代 ,自 70年代末期以来 ,一直被认为属于中、上元古代。本文通过在总面积为 60 0 km2 的西部凹陷中段系统、详尽的牙形石生物地层研究 ,并结合疑源类、小壳化石以及岩石地层学资料 ,确认研究区内古潜山顶部地层的时代主要为晚寒武世至早奥陶世。中、上元古代地层在研究区内虽然存在 ,但分布极其局限。从而 ,彻底改变了2 0年以来对该地区古潜山地层划分和对比上的传统认识。     

皖南震旦纪-早寒武世沉积岩有机碳、氮元素记录

安徽南部晚震旦世蓝田组、皮园村组和早寒武世荷塘组主要由黑色页岩和硅质岩组成。分析结果表明,蓝田组和荷塘组的总有机碳(可达10％--18％)和总有机氮(可达2．0‰--2．6‰)的高含量,应归于富有机质埋藏所致,反映新元古代末次冰期后和早寒武世海洋浮游生物处于大发展时期。由于海洋植物的光合作用产生大量O2,并消耗大量CO2,导致大气中O2／CO2比率明显增加,为震旦纪晚期多细胞真核生物的辐射、后生动物的出现和‘寒武纪生物大爆发’提供了条件。蓝田组黑色页岩中部的有机碳与有机氮含量大体呈现正比例增加,并且分别达到17．74％和2．66‰的最高值,与该剖面发现的蓝田植物群相对应;荷塘组黑色页岩的有机碳和有机氮垂直分布曲线之间呈现相互背离,即有机氮含量与时增加,而有机碳含量与时减少,与扬子地台相应的地层层位产生的澄江动物群相对应,表明TON和TOC分布特征有可能与早期生物演化历程相关。     

The nervous and circulatory systems of a Cretaceous crinoid: preservation,palaeobiology and evolutionary significance

Featherstars, comatulid crinoids that shed their stalk during their ontogeny, are the most species-rich lineage of modern crinoids and the only ones present in shallow water today. Although they are of considerable palaeontological interest as a ‘success story’ of the Mesozoic Marine Revolution, their fossil record is relatively species-poor and fragmentary. New Spanish fossils of the Cretaceous featherstar Decameros ricordeanus preserve the shape and configuration of nervous and circulatory anatomy in the form of infilled cavities, which we reconstruct from CT scans. The circulatory system of D. ricordeanus was relatively extensive and complex, implying a pattern of coelomic fluid flow that is unique among crinoids, and the peripheral parts of the nervous system include linkages both to the circulatory system and to the surface of the body. A phylogenetic analysis (the first to include both living and fossil featherstars and which includes characters from internal anatomy) recovers D. ricordeanus among the lineage of featherstars that includes Himerometroidea, Tropiometra and ‘Antedonoidea’, among others. D. ricordeanus is larger than almost any modern featherstar, and its elaborate coelomic morphology appears to be a consequence of positive allometry. All featherstars with coelomic diverticula are shown to belong to a single comatulid subclade, and this feature may constitute a synapomorphy of that group. Some preservation of cavities corresponding to soft tissue is probably not exceptional in fossil crinoids, providing an opportunity to study the diversity and evolution of extinct anatomical systems typically only preserved in Lagerstätten.     

内蒙古清水河晚寒武世崮山期三叶虫

记述内蒙古清水河刘家窑上寒武统崮山组中下部灰色中一薄层含鲕粒灰岩．泥质条带灰岩夹竹叶状灰岩中的三叶虫化石１０种,其中３新种（包括１新亚种）,分属于７属４科。     

苔藓动物的谱系发生位置与早期分歧时间(英文)

苔藓动物是后生动物系统进化研究中的关键类群之一。作者基于冠轮动物38个代表种类的LSU和SSU rRNA组合基因序列数据,以二胚层动物为外类群,运用最大简约法、最大似然法和贝叶斯分析法,重建了触手冠担轮动物的系统树;同时,基于分子钟的方法推测了苔藓动物主要类群的起源与分歧时间。分子系统学的分析结果表明:触手冠动物并非都是单种系群;而苔藓动物则为单种系群,并构成触手冠担轮动物的基部类群。尽管苔藓动物的最早化石记录仅发现于奥陶纪特马豆克期地层中,谱系年代分析结果显示:苔藓动物及其主要谱系在新元古代已经分化;其中,苔藓动物祖先类群的起源时间约为634Ma,基部类群(被唇纲)与其它苔藓动物的分歧时间大约为607Ma。这一结果说明,化石记录始于奥陶纪的苔藓动物根植于新元古代的埃迪卡拉纪,早期祖先类群可能缺乏钙化骨骼,因而不易保存为化石。从而支持关于动物主要门类起源于新元古代的谱系年代学研究成果。     

湘西晚寒武世多节类三叶虫新种及Erixanium属首次发现

文中描记 3个多节类三叶虫新种 :Hardyoidesdamaensissp .nov .,Meringaspisdamaensissp .nov .,andRhyssometopus (Rostrifinis)nitidussp .nov .,均产自湘西凤凰花桥组中部。同时描记首次在江南斜坡带中发现的Erixanium一属的保留命名种Erixaniumcf.E .sentum。Erixanium是全球性分布的多节类三叶虫 。