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帽状动物壳体 lathamellids 类化石包括 Lathamella caeca, Lathamella sp. nov. 以及 Lathamella symmetrica sp. nov. 三种,目前仅发现于四川峨嵋麦地坪下寒武统麦地坪组上段地层,它们皆以磷质内核方式保存.通过内核化石表面所复制的原始壳体微细构造印痕的研究表明,易漏螺类壳体为双层结构:内层——纤晶层,外层——棱柱层;其壳体原始成分可能为文石质.据上述现象推断,lathamellids 并非为磷质无绞纲腕足类,相反,而与软体动物更为接近,但其在壳腔内具—纵向中突,主要位于壳顶附近,很难与已知的任何一类软体动物直接对比,可能为一类独特的、已经绝灭了的软体动物的1个早期分支. 相似文献
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寒武纪早期帽状动物壳体Lathamellids类的微细构造... 总被引：1，自引：1，他引：1
帽状动物壳体 lathamellids 类化石包括 Lathamella caeca*, Lathamella sp. nov. 以及 Lathamella symmetrica sp. nov. 三种,目前仅发现于四川峨嵋麦地坪下寒武统麦地坪组上段地层,它们皆以磷质内核方式保存.通过内核化石表面所复制的原始壳体微细构造印痕的研究表明,易漏螺类壳体为双层结构:内层——纤晶层,外层——棱柱层;其壳体原始成分可能为文石质.据上述现象推断,lathamellids 并非为磷质无绞纲腕足类,相反,而与软体动物更为接近,但其在壳腔内具—纵向中突,主要位于壳顶附近,很难与已知的任何一类软体动物直接对比,可能为一类独特的、已经绝灭了的软体动物的1个早期分支. 相似文献
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新疆寒武纪早期单壳类软体动物化石分类学与生物地层学 总被引：2，自引：0，他引：2
作者系统描述了新疆阿克苏-乌什地区下寒武统玉尔吐斯组中上部单壳类软体动物化石10属10种,其中包括3个新种、3个老种和4个未定种,它们是Shabaktiella multiformis sp.nov.,Ilsanella acuta sp.nov.,Xianfengella yuertusiensis sp.nov.,Parcaconus xinjiangensis,Protostenotheca xinjiangensis,Aldanella attlebo-rensis,Obtusoconus sp.,Yochelcionella sp.,Bemella sp.和Mellopegma sp..上述10个属种基本上代表了玉尔吐斯组单壳类软体动物的面貌特征.文中介绍了本研究区10个属和属级以上分类系统在国际学术界的意见分歧后,重申了以壳的对称性和有无肌痕确定纲级界线的最佳分类原则,提出了应用壳型划分目级分类单元和口缘形状、壳顶与口缘的相对位置划分科级分类单元的可行性和有效性,但是不能接受把所有单板状软体动物化石通常被归入单板纲的做法,因为寒武纪早期一些单板状软体动物化石不一定符合单板纲的真实含义.文中还回顾了近二十年来建立的始单板纲(Eomonoplacophora)(Missarzhevsky,1989),太阳女神螺纲(Helcionelloida),背壳肌纲(Tergomya)(Peel,1991a,b)和似腹足纲(Paragastropoda)(Linsley & Kier,1984)等纲级的新概念.还有一些早期软体动物专家将许多单板状(包括帽状和螺旋状)化石归入单板纲(Runnegar et al.,1976,1985),而另有一些中青年软体动物专家继承传统理念,将它们归入了腹足纲(Parkhaev in.Alexander et al.,2001).钱逸和本格森将早期单壳类软体动物化石分成了五大形态类别,未确定科级以上分类单元名称(Qian & Bengtson,1989).总之,目前纲级分类单元界线不清,目级以下分类单元十分混乱,在没有全面清理早期单壳类软体动物百余个属和属级以上分类单元之前,是难以统一本文研究的早期单壳类软体动物10个属和属级以上分类系统.我们认为在确定属级以上分类系统及其与之密切相关的演化谱系关系时,不是利用理论前提,而是在不间断的剖面上对单壳类软体动物化石进行逐层采集并对其构造要素的详细研究,才能使得出的结论和提出的新分类系统发生错误的几率最小.文中还归纳和总结了本研究区玉尔吐斯组中上部单壳类软体动物群面貌的六大特点,其中二点最重要:1)该动物群与梅树村期微软体动物群的面貌有明显的差别,它缺失了梅树村期微软体动物群中最原始、最特征、最丰富的类群,如笠帽状的马哈螺类化石Maikhanella,Purella等和螺旋状的始旋螺类化石Archaeospira等.但是该动物群面貌却与邻区的哈萨克斯坦Atdabanian期的微软体动物和我国峡区西蒿坪动物群面貌接近,出现了许多相同或相似的属种,如Shabaktiella,Mellopegma,Aldanella,Yochelcionella等.2)该动物群共生有全球分布的相当于筇竹寺期的标准化石,如原牙形类Gapparodus,Amphigeisina,Hagionella等,有口唇并有背腹分异和复杂口盖的软舌螺类Microconus,Pachytheca等,具有肉茎孔和铰合面的有铰腕足类和像Obolus那样的原始无铰腕足类,有各种形态类型的金臂虫Dabashanella,Liangshanella等,还有可疑的三叶虫颊刺等.上述信息足以说明玉尔吐斯组中上部地层时代应属筇竹寺期而非梅树村期,从而解决了长期以来有关玉尔吐斯组时代归属的争议. 玉尔吐斯组单壳类软体动物群的研究,再次证实了寒武纪生命大爆发期间,早期单壳类软体动物与小壳动物群一起经历了三次大发展和三次大绝灭事件.这在早期单壳类软体动物化石分类学、生物地层学和早期演化史上均有较高的科学价值. 相似文献
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《微体古生物学报》2016,(1)
扬子地台北缘在寒武纪筇竹寺期—沧浪铺期出现海退,该时期的仙女洞组属浅海碳酸盐岩与碎屑岩的混合沉积单元,分布于陕西南部及四川北部。陕南南郑福成和碑坝剖面组成完整仙女洞组序列,其中包含8期生物礁相单元。单层礁体为米级厚度,形态特征显示丘状隆起或平缓延伸。水体的清澈度、深度以及水动力强度变化对各期礁相单元生长的控制力度因时而异,陆源碎屑数次侵入导致海水浑浊度增高,点断了礁体生长。礁灰岩微相类型包括钙质微生物粘结岩、古杯-钙质微生物绑结岩、古杯漂砾-砾屑灰岩、粒泥状-泥粒状灰岩以及泥状灰岩。早期礁灰岩中钙质微生物粘结岩含量丰富,之后古杯绑结岩在礁灰岩构建中具有丰度增长的趋势,且上部礁灰岩层位中不规则古杯占主要地位。仙女洞组沉积晚期海水变浅和水动力条件增强,常见漂砾灰岩和砾屑灰岩。 相似文献
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Anabarites trisulcatus是寒武纪早期一类三辐射对称的管栖生物,推测营群居的方式生活在浅海。本文对来自陕南宁强石钟沟剖面寒武系底部宽川铺组的Anabarites trisulcatus进行了计算机流体力学分析。根据化石形态构建3D模型,依据推测的生活环境设计流域参数,进行了单体与群居两种不同生活方式下的流体动力学模拟,结果表明:(1)水动力条件对于底栖Anabarites trisulcatus而言是重要的影响因素;(2)Anabarites trisulcatus以群居的方式生活阻力系数更小,更有利于生存。本文使用计算流体力学的方法对长期存在的功能和生态假说进行定量检验,是微体化石研究新思路的一次有益尝试。 相似文献
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始海百合类是贵州寒武纪杷榔动物群和凯里生物群代表性化石类群。产出杷榔动物群和凯里生物群的杷榔组和凯里组主要由灰绿色、灰色的泥、页岩组成,始海百合类化石保存在2个组中上部的泥、页岩中,化石保存好,丰度高,是陆棚斜坡较深水环境生态类群的典型代表。本文基于来自杷榔组的36块Guizhoueocrinus yui,29块Protogloboeocrinus yini标本,和凯里组的20块Sinoeocrinus lui,20块Globoeocrinus globulus标本,采用几何形态测量方法和传统形态测量方法,对每块标本萼部选定了4个界标点(landmark),进行数理统计和几何形态的定量分析。发现寒武纪始海百合类的萼部尺寸上差异较小,在形态上,杷榔组的Protogloboeocrinus yini和Guizhoueocrinus yui萼形相似,均偏细长形,而凯里组的Sinoeocrinus lui和Globoeocrinus globulus萼形差异较大,口部区域宽度均出现增大,萼茎连接处宽度则出现变大和变小两种趋势。结果说明:同一生态环境下寒武纪早期的Guizhoueocrinus yui,和中期的Sinoeocrinus lui的萼在演化上具连续性,细长的萼与长茎能够让始海百合个体更有效捕食上部水域的食物,而寒武纪早期的Protogloboeocrinus yini和中期的Globoeocrinus globulus的萼在形态上具有演化上的连续性。球状的萼配合粗短的茎,可以增强始海百合个体的稳定性,以适应更强的水动力环境,表明出现了生态位的扩张。 相似文献
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桂东北较深水相前寒武纪-寒武纪之交的硅质微生物岩 总被引：2，自引：0，他引：2
扬子地台东南缘较深水相区的前寒武纪-寒武纪过渡地层为一套以硅质岩和硅质碎屑岩为主的黑色岩系沉积.过去对这套硅质岩的沉积模式有多种解释,而且由于生物化石的匮乏而很难确定前寒武纪-寒武纪界线的位置.桂东北地区三江剖面前寒武纪-寒武纪过渡地层老馕组硅质岩中保存有良好的微生物岩.在根据有机碳同位素和微体化石确定的前寒武纪-寒武纪界线之下,微生物岩以叠层石-凝块石组合为标志,具有与台地相同期地层类似的特征;在界线之上,则以集群出现的球形至椭球形石英质微球体组合和典型的微生物膜沉积结构为主要特征.微生物席/膜的硅化可能是前寒武纪-寒武纪之交较深水相硅质岩沉积的重要模式. 相似文献
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选择理由：进化速度的估计对于系统发生,分子进化的研究非常重要,但准确地估计物种的进化速度又是非常困难的。关注这方面的研究对于从事相关领域的研究者就很重要了。 相似文献
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WEIMIN FENG IWAO KOBAYASHI 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2004,37(3):263-270
Acrotretoids, one of the oldest brachiopod groups, are abundant in the Lower Cambrian Jiulaodong Formation. The shell of Linnarssonia sp. is composed of two layers: a primary layer and a columnar secondary layer. The primary layer is mostly exfoliated, resulting in exposure of the openings to the central canal of the columns. Filae are seen on the surface of the columnar layer, indicating that the columnar secondary layer has influenced changes in ornament on the shell surface. The larval shell has only very weak ripples; the post-larval shell has obvious concentric ribs. Small pits of variable shape cover almost the entire shell surface. The secondary layer is composed of several columnar laminations, each of which comprises both the upper and lower laminae and the cylindrical columns between them. On the inner side of shell the thin columnar laminations increase. The new microstructural data show that two shell layers are developed in Early Cambrian acrotretoid brachiopods; the columnar lamination may be a primitive feature of the microstructural development of the Brachiopoda and may help establish the affinity between different stem-group brachiopods. 相似文献
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贵州早、中寒武世斗篷海绵科(Choiidae)的发现 总被引：4，自引：3，他引：4
本文描述了贵州遵义下寒武统牛蹄塘组生物群和台江中寒武世凯里生物群中保存完整的斗篷海绵科(Choiidae)中斗篷海绵(Choia)和小斗篷海绵(Choiaella)化石标本,共计2属2种2未定种：Choia zunyiensis sp.nov.,Choia sp.,Choiaella avata sp.nov.和Choiaella sp.。Choia分布很广．在我国下寒武统澄江生物群及北美中寒武统的四大生物群中均有产出。Choiaella原仅产于我国澄江生物群,凯里生物群中Choiaella的发现使其时代上延至中寒武世。贵州早、中寒武世斗篷海绵科的发现及研究为海绵动物的早期演化及古地理学等方面的研究提供了重要的新材料。 相似文献
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SUSANNAH M. PORTER 《Palaeontology》2008,51(4):865-879
Abstract: Chancelloriids are problematic, sac‐like animals whose sclerites are common in Cambrian fossil assemblages. They look like sponges, but were united with the slug‐like halkieriids in the group Coeloscleritophora Bengtson and Missarzhevsky, 1981 based on a unique mode of sclerite construction. Because their body plans are so different, this proposal has never been well accepted, but detailed study of their sclerite microstructure presented here provides additional support for this grouping. Both taxa possess walls composed of a thin, probably organic, sheet overlying a single layer of aragonite fibres orientated parallel to the long axis of the sclerite. In all halkieriids and in the chancelloriid genus Archiasterella Sdzuy, 1969 , bundles of these fibres form inclined projections on the upper surface of the sclerite giving it a scaly appearance. On the lower surface of the sclerite, the projections are absent. This microstructure appears to be unique to chancelloriids, halkieriids, and their relatives, siphogonuchitids and sachitids. (The sclerites of another putative halkieriid relative, Wiwaxia Walcott, 1911 , are unmineralized, making direct comparisons impossible.) Thus, similarity both at the level of sclerite construction and the level of sclerite microstructure suggests that chancelloriid, halkieriid, sachitid, and siphogonuchitid sclerites are homologous. The difference in chancelloriid and halkieriid body plans can be resolved in two ways. Chancelloriids either represent a derived condition exhibiting complete loss of bilaterian characters or they represent the ancestral condition from which the bilaterally symmetric halkieriids, and the Bilateria as a whole, derived. The latter interpretation, proposed by Bengtson (2005) , implies that coeloscleritophoran sclerites (‘coelosclerites’) are a plesiomorphy of the Bilateria, lost or transformed in descendent lineages. Given that mineralized coelosclerites appear in the fossil record no earlier than c. 542 Ma, this in turn implies either that the Ediacaran record of bilaterians has been misinterpreted or that coelosclerite preservability increased at the beginning of the Cambrian Period. The former is difficult to reconcile with Ediacaran trace and body fossil evidence, but the latter may be possible, reflecting either independent mineralization of organic‐walled sclerites in chancelloriids and halkieriids or the opening of a taphonomic window that favours coelosclerite preservation. 相似文献
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Hyoliths are a group of Palaeozoic fossils with calcareous shells whose affinities remain controversial. As their shells were originally aragonitic, their fossils are usually coarsely recrystallized, and few data on their microstructure are available. We report hyoliths from the middle Cambrian (Drumian, Floran) Gowers Formation of the eastern Georgina Basin, Queensland. These are preserved as phosphatic internal moulds, often with the inner layers of the shell also partly replaced by phosphate. Microstructural details preserved by this early diagenetic phosphatization show that these hyolith conchs were originally composed of fibrous crystallites, c. 0.5 μm wide, parallel to one another and to the inner surface of the shell. In several species, the fibres are arranged in a plywood‐like structure composed of multiple lamellae with a different fibre orientation in each lamella: often they are transversely oriented (relative to the long axis of the conch) in the inner part of the wall and longitudinally oriented in the outer part. Opercula also show a microstructure of parallel fibres. The lamello‐fibrillar microstructure we report from hyoliths is reminiscent of microstructures of many Cambrian molluscs; that this microstructure is found in both conchs and opercula suggests that these structures are serial homologues of one another, and in this respect they resemble brachiopod valves. As with many other biological plywoods, the hyolith shell probably records self‐organization in a liquid‐crystal‐like organic matrix. This provided a straightforward way to construct a material that could resist stresses from different directions, offering an effective defence against predators. 相似文献
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by MICHAEL J. VENDRASCO SUSANNAH M. PORTER† ARTEM KOUCHINSKY‡ GUOXIANG LI§ CHRISTINE Z. FERNANDEZ¶ 《Palaeontology》2010,53(1):97-135
Abstract: Numerous new cases of preserved shell microstructure were discovered in molluscs from the Middle Cambrian Gowers Formation (Ptychagnostus atavus/Peronopsis opimus Zone, Floran Stage) in the Georgina Basin, Australia. The new data provide further evidence that, by the Middle Cambrian, molluscan shell microstructures were diverse, and many molluscs had a complex shell with multiple types of shell microstructure. In addition, many new occurrences of laminar microstructures are described herein. For many, the nature of these laminar microstructures is not known, but in three species the microstructure is foliated calcite, and in at least two the microstructure is more likely to have been calcitic semi‐nacre, a type of microstructure known in brachiopods and bryozoans but unknown in modern molluscs. This commonality among these three closely related lophotrochozoans underscores a similar mechanism of biomineralization. Moreover, these observations suggest a prevalence of calcite‐shelled lineages among molluscs from the Middle Cambrian, a time of calcite seas. In addition, the broad occurrence of laminar, nacre‐like microstructures in many of these fossils reveals how widespread these strong (fracture‐resistant) microstructures were in Middle Cambrian molluscs. Additionally, a few specimens of Yochelcionella preserve imprints of a bilaterally symmetrical pair of muscle scars. New taxa described here include Corystos thorntoniensis gen. et sp. nov., Yochelcionella snorkorum sp. nov., Yochelcionella saginata sp. nov., and Anhuiconus? agrenon sp. nov. 相似文献
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陕西镇巴早寒武世海绵骨针化石 总被引：1，自引：0，他引：1
作者对采自陕西省镇巴县下寒武统西蒿坪段和水井沱组下部碳酸盐岩地层的海绵骨针化石进行了研究。三叶虫及小壳化石的生物地层学资料表明西蒿坪段和水井沱组下段属于筇竹寺阶。化石经室内醋酸浸泡处理后获得,骨针化石保存较好、类型多样,其中属于六射海绵纲的骨针3类,普通海绵纲的骨针6类,分类未定的骨针1类(Nabaviellasp.);并详细地对各类骨针化石进行了描述。虽然普通海绵骨针类型多样,但六射海绵的骨针丰度远高于普通海绵。简要地探讨了海绵骨针的保存方式,对比和分析了西蒿坪段和水井沱组海绵骨针化石组成的差异。结合同时代产自皖南荷塘组和云南澄江动物群中特异保存的海绵软躯体化石资料,认为虽然海绵动物起源于新元古代末期,但躯体海绵化石和骨针化石都显示海绵动物的大辐射事件发生在早寒武世筇竹寺期。 相似文献
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黔东早—中寒武世凯里组疑源类组合及其界线意义 总被引：13，自引：0，他引：13
通过对台江八郎和丹寨两条剖面凯里组中疑源类化石的分析,研究,台江剖面产疑源类化石有17属35各（12未定种）,其中以Leiosphaeridia,Synsphareidium,Cymatiosphaera,Pterospermella最为丰富,可划分为3个组合,即Cymatiosphaera cf.cristata-Fimbriaglomerella memebrancea组合,Cristallinium-Micrhystridium-Pterospermella组合和Dictyotidium-Granomarginata组合,丹寨平寨剖面凯里组所产疑源类化石有：13属21种（5未定种）,同样划分为3个组合,即Leiosphaeridia-Tasmanites组合,Retisphaeridium-Micrhystridium tentatium组合和Baltisphaeridium-Bubomorpha hunjiangensis组合,本文对两条剖面中的凝源类化石的组成,相对含量做了详细的统计,发现在八郎剖面9－2层和平寨剖面3层疑源类的丰度,分异度开始发生明显的变化,表现由早寒武世向中寒武世疑源类组合面貌的转变,这一疑源类转变层位正好是与三叶虫划分的中,下寒武统界线的层位位置相一致,这充分表明疑源类化石可作为划分中,下寒武统的极有价值的微体生物化石证据。 相似文献
18.
Xing Wang Jian Han Jean Vannier Qiang Ou Xiaoguang Yang Kentaro Uesugi Osamu Sasaki Tsuyoshi Komiya 《Palaeontology》2017,60(6):853-867
We describe here Sinaster petalon gen. et sp. nov., a new embryonic form from the c. 535 million‐year‐old Kuanchuanpu Formation of South China (Ningqiang, Shaanxi Province). The excellent three‐dimensional, phosphatic preservation of these microfossils allowed us to use x‐ray microtomographic techniques to make accurate reconstructions of their internal structures and to compare their anatomy point‐by‐point with that of extant cnidarians and other animal groups. Sinaster petalon has anatomical features typical of extant Medusozoa (Cnidaria), such as coronal muscles, perradial and adradial frenula, interradial septa, accessory septa, gonad‐lamellae, tentacle buds and perradial pockets. Although Sinaster cannot be straightforwardly assigned to any crown‐group within Medusozoa, the presence of marginal lappets and endodermal lamellae suggests that it is closer to Cubozoa and Scyphozoa than to any other group of modern cnidarians. The tentative placement of Sinaster within the stem‐group Cubozoa is justified by the presence of a velarium supported by a frenulum. The cubozoan affinities of Sinaster are also supported by cladistic analysis. 相似文献