奥陶纪苔藓动物的多样性演变——兼论苔藓动物的起源

苔藓动物是一类多为海生、滤食性的群体生物。奥陶纪是苔藓动物发生、演化辐射和灭绝的重要时期,也是苔虫礁形成的最早时期。已知最老的化石苔藓动物发现于中国特马豆克晚期。构成苔藓动物基本分类框架的狭唇纲(包括变口目、隐口目、泡孔目和管孔目)和宽唇纲(包括窗孔目和栉口目)也都是在奥陶纪时期逐步形成的,其中,变口目出现于特马豆克期Tr2时间段,在弗洛期和大坪期,多样性较低,但从达瑞威尔期开始,经桑比期至凯迪期,多样性不断增高,并出现辐射。隐口目(特别是"双叶类隐口目苔虫")也经历了与变口目相类似的发展过程,但它首次出现的时间要相对略迟于变口目。这两个目在整个奥陶纪苔藓动物群中一直占据主导地位。泡孔目、管孔目和窗孔目,先后首次出现在弗洛期Fl2时间段、大坪期Dp1和Dp2时间段,但它们在整个奥陶纪期间一直处于低多样性态势。至于栉口目,它首次出现的时间可能更迟,在凯迪期Ka4时间段,犹如昙花一现。苔藓动物的演化在接近奥陶纪末时呈两幕式灭绝,一次发生在凯迪期Ka2时间段(可能相当于塔凯和安斯蒂的"拉夫塞伊灭绝"),另一次发生在赫南特期Hi2时间段(可能相当于塔凯和安斯蒂的"赫南特灭绝")。分子生物学和形态学证据表明,苔藓动物属原口动物,而不是以前长期认为的后口动物,或介于原口动物和后口动物之间的过渡类型;而且,苔藓动物与腕足动物、帚形动物之间没有直接的亲缘关系。苔藓动物可能起源于一种叫原内肛动物的生物,它们的目一级分类单元之间的系统发育关系目前尚未形成共识,本文绘制的谱系图还有待于化石记录的不断补充和分子生物学研究的逐步介入以使其日趋完善。     

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。     

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。     

新疆塔里木盆地中部和北部台地上奥陶统良里塔格组岩心中的泡孔目、隐口目和窗孔目苔虫

新疆塔里木盆地奥陶系良里塔格组礁滩相非常发育,部分地区泡孔目、隐口目和窗孔目苔虫化石非常丰富,本文首次系统描述了塔里木盆地巴楚-塔中和塔北碳酸盐台地部分取心井上奥陶统良里塔格组的泡孔目、隐口目和窗孔目苔虫7科11属13种,包括1个新种和6个未定种,分别为Lunaferamita nevadensis Utgaard,L. vesicu-larissp.nov.,L.sp.,Graptodictya meneghinii(Vinassa de Regny),Chazydictya sp.,Rhinidictya nicholsoni Ulrich,Metadictyacf.crassa(Hall),Trigonodictya acuta(Hall),Stictoporella sp.,Chasmatopora spatiosa Ariun-chimeg,Ralfinellasp.,Moyerella sp.,Moorephylloporina sp.。其中,隐口目细枝状的Rhinidictya和网状的Chasmatopora,Moorephylloporina在塔中和巴楚地区横向及纵向地层中分布非常广泛。     

藏北中侏罗世窗孔类的发现和唇口类的起源

本文建立了新科Fenestraporidae及其一个新属Auiculofenestella和它的两个新种A.triapertalis,A.que-napertalis被建立和描述了,它们发现于藏北羌塘盆地中侏罗世巴柔期的地层内,新属和限于北美和中亚高加索地区早泥盆世晚期和中泥盆世的已知的窗孔苔虫（Fenestrapora)。都显示了似鸟头体的构造,然而,新属中所有的这种似鸟头体构造,只分布于横枝上,本文也讨论了窗孔苔藓动物和其它各类苔藓动物之间可能的亲缘关系,作者推测,窗孔苔藓动物是由隐口苔藓动物的叶孔苔虫（Parachasmatopora)经中奥陶世的原始的窗孔苔藓动物Moore-phylloporina发展来的,新属的发现更进一步提供了支持这样一种假设,即：“唇口苔藓动物是由窗孔苔虫经新属乌头窗格苔虫（Auiculofenestella)发展来的”假设的重要证据 。     

新疆塔里木塔中井区上奥陶统良里塔格组的生物绑结岩

塔里木板块塔中井区上奥陶统凯迪阶良里塔格组灰岩中底栖固着型的钙质微生物、钙藻以及动物苔藓虫、珊瑚、层孔虫,可通过障积、盖覆和粘结等方式形成多种类型的生物绑结岩。对15口井部分岩芯以常用的绑结岩分类方案作岩石学微相分析,并描记底栖固着型生物颗粒的形成特征。菌藻类可在内碎屑表面以包结方式形成粘结岩;钙藻,特别是分枝状钙藻可形成障积岩;层孔虫可被隐藻层纹包结,也可单独形成小型盖覆岩;床板珊瑚格架岩可大量障积生屑和灰泥基质;苔藓虫在动物格架岩比例上占优,可与菌藻类粘结岩互相包结生长,也可独立形成局部小型障积岩。对比巴楚露头区同期藻丘中的绑结岩特征,显示塔中良里塔格组代表晚奥陶世由高生物多样性形成的礁滩复合体生态群落。     

基于18S rRNA基因序列分析唇口目苔藓动物主要类群的系统发生关系

对隶属于3亚目、5次目、20科、23属共25个种类的唇口目(裸唇纲)苔藓虫18S rRNA基因部分序列进行了序列测定.结合从GenBank中获得的该类群其它7个种类的18S rRNA基因同源序列,以序列分析软件对其序列组成和变异进行了比较分析;同时,以羽苔虫(被唇纲)和管孔苔虫(窄唇纲)为外类群,以邻接法和最大简约法重建了它们的系统发生树,分析了该目主要类群系统发生关系.序列分析结果显示:经比对后序列长度为884 bp,其中保守位点241个,可变位点643个,简约信息位点357个;A,T,C和G 4碱基平均含量分别为23.8%、22.8%、24.4%和28.9%.分子系统树表明:本研究所有有囊类构成1个单系群,其中檐胞次目的几种苔虫位于皮壳次目内部;无囊类形成1个多系群,其中的亚目级(新唇口亚目)和次目级分类阶元(枝室次目、假软壁次目和隐壁次目)也都为多系发生,这些结果与前人的分子系统学研究结果大体一致,而与传统的形态分类体系间存在明显的冲突.     

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。     

滇东北奥陶纪三叶虫的地层分布

详细讨论滇东北奥陶纪的岩石地层和动物群特征,初步建立区内的三叶虫地层序列,据此可靠确定各有关岩组的时代。该地区除普遍缺失早奥陶世早期的沉积外,依次发育了红花园组(特马豆克末期—弗洛初期),湄潭组(弗洛期—达瑞威尔初期),风洞岗组(达瑞威尔早—晚期),十字铺组(达瑞威尔末期—桑比早期)、宝塔组(桑比晚期—凯迪早期),盐津组(晚凯迪早期)、五峰组(晚凯迪晚期)及观音桥组(赫南特期),岩相与黔北的相应岩组可作大致对比,而三叶虫动物群的组成和序列则大体与当时同属扬子陆块西部边缘的沉积区包括滇东、滇东南、黔北、川中、重庆、陕南及安徽和县等地区相似。共记述本区奥陶纪三叶虫计19属27种,分属14科。并对其中的一个新种Hungioides yanjinensis sp.nov.以及两个未命名的新种Abulbaspis sp.nov.和Plaesiacomiasp.nov.作系统描述。Abulbaspis过去仅报道于华北和哈萨克斯坦地区的达瑞威尔阶,而在本地区则产于桑比阶上部—凯迪阶下部;Plaesiacomia广泛分布于达瑞威尔阶—桑比阶西泛冈瓦纳地区,在滇东北的发现不但将该属的分布区域扩大到了东泛冈瓦纳地区,而且因其产出于大坪中期的层段,表明该属可能起源于东泛冈瓦纳,尔后才向西迁移的;这两属在扬子区的首次发现,对于进一步研究奥陶纪不同区块间的三叶虫动物群的扩散和交流具有重要意义。     

滇东北奥陶纪三叶虫的地层分布北大核心CSCD

详细讨论滇东北奥陶纪的岩石地层和动物群特征,初步建立区内的三叶虫地层序列,据此可靠确定各有关岩组的时代。该地区除普遍缺失早奥陶世早期的沉积外,依次发育了红花园组(特马豆克末期—弗洛初期),湄潭组(弗洛期—达瑞威尔初期),风洞岗组(达瑞威尔早—晚期),十字铺组(达瑞威尔末期—桑比早期)、宝塔组(桑比晚期—凯迪早期),盐津组(晚凯迪早期)、五峰组(晚凯迪晚期)及观音桥组(赫南特期),岩相与黔北的相应岩组可作大致对比,而三叶虫动物群的组成和序列则大体与当时同属扬子陆块西部边缘的沉积区包括滇东、滇东南、黔北、川中、重庆、陕南及安徽和县等地区相似。共记述本区奥陶纪三叶虫计19属27种,分属14科。并对其中的一个新种Hungioides yanjinensis sp.nov.以及两个未命名的新种Abulbaspis sp.nov.和Plaesiacomiasp.nov.作系统描述。Abulbaspis过去仅报道于华北和哈萨克斯坦地区的达瑞威尔阶,而在本地区则产于桑比阶上部—凯迪阶下部;Plaesiacomia广泛分布于达瑞威尔阶—桑比阶西泛冈瓦纳地区,在滇东北的发现不但将该属的分布区域扩大到了东泛冈瓦纳地区,而且因其产出于大坪中期的层段,表明该属可能起源于东泛冈瓦纳,尔后才向西迁移的;这两属在扬子区的首次发现,对于进一步研究奥陶纪不同区块间的三叶虫动物群的扩散和交流具有重要意义。     

Early Ordovician bryozoans from north-western Russia

ABSTRACT. A bryozoan assemblage from the Billingen Stage of north-western Russia (Ingria) is apparently the oldest known in the world. It consists of six species distributed among the trepostomate genera Esthoniopora Dianulites, Revalotrypa Phragmophora and Hemiphragma . Two species are new: Phragmophora lavaense Pushkin, sp. nov. and Hemiphragma priscum Pushkin, sp. nov. The bryozoans are characteristic of the medium diversity benthic fauna of uncertain origin which migrated into the Baltic Basin during Billingen time (late Prioniodus elegans — early Oepikodus evae zones). The Billingen bryozoans have a close similarity to the late Arenig bryozoan faunas of Baltoscandia that are also dominated by trepostomates, but differ significantly from the low diversity late Arenig bryozoan assemblages of North America, Ireland, North China, Vajgach and Novaja Zemlja.     

Horizon of the oldest known bryozoans (Ordovician)

Among the six species of fossil bryozoans described by Xia et al. [Xia, F.S., Zhang, S.G., Wang, Z.Z., 2007. The oldest bryozoans: new evidence from the late Tremadocian (Early Ordovician) of East Yangtze Gorges. Journal of Paleontology 81 (6), 1308–1326] from the Fenghsiang Formation of the Chenjiahe section of Yichang and the Guanzhuangping section, Liujiachang Town of Songzi, the Yangtze Gorges, Nekhorosheviella nodulifera occurs in the pristinus Conodont Subzone (lower Subzone of deltifer Conodont Zone) and the five other species are associated with the conodont Paltodus deltifer deltifer and the graptolites Acanthograptus sinensis and A. erectoramus. Based on the conodonts and graptolites, this bryofauna stratigraphically corresponds to the A. sinensis Graptolite Zone or P. deltifer Conodont Zone. The bryofauna is of Tremadocian Age (Early Ordovician) and represents the oldest bryozoans so far as known.     

Frasnian bryozoans (Late Devonian) from the Khoshyeilagh Section,Alborz Mountains (northern Iran)

A bryozoan fauna containing seven species is described from the Upper Frasnian (Upper Devonian) rocks in the Khoshyeilagh Section, Alborz Mountains (northern Iran). The studied bryozoan assemblage includes one new trepostome species, Eridotrypella alborzensis sp. nov., an additional four species identified at species level: two trepostomes, Minussina akkayaensis Volkova, 1974 and Leptotrypella inaudita Morozova, 1961, and two rhabdomesine cryptostomes, Bigeyella mariae (Morozova, 1961) and Saffordotaxis multispinata (Morozova, 1955). Furthermore, two species are described in open nomenclature: the trepostome Schulgina sp. and the rhabdomesine cryptostome Nicklesopora sp. The studied fauna shows a close similarity at the species level between northern Iran and the Altai-Sayan Folded Belt (Russia), south China, and Transcaucasia.     

Symbiosis of cornulitids with the cystoporate bryozoan Fistulipora in the Pridoli of Saaremaa,Estonia

Cornulites sp. and Fistulipora przhidolensis formed a symbiotic association in the Pridoli (latest Silurian) of Saaremaa Island, Estonia. This Cornulites sp.–F. przhidolensis association is the youngest example of cornulitid–bryozoan symbiosis. Symbiosis is indicated by intergrowth of both organisms. The cornulitids are completely embedded within the cystoporate bryozoan colony, leaving only their apertures free on the growth surface of bryozoan. In terms of food competition, this association could have been slightly harmful to F. przhidolensis as Cornulites sp. may have been a kleptoparasite. There may have been a small escalation in the evolution of the endobiotic life mode of cornulitids as the number of such associations increased from the Ordovician to Silurian. It is likely that Palaeozoic bryozoan symbiosis reached its maximum in the Late Ordovician. Most of the symbiotic bryozoans in the Palaeozoic are trepostomes, and the diversity of symbiotic associations was also greatest among trepostomes.     

UPPER ORDOVICIAN BRYOZOANS OF THE PIN FORMATION (SPITI VALLEY, NORTHERN INDIA)

Abstract: Twenty‐nine species of bryozoans from the Upper Ordovician–Lower Silurian Pin Formation (Spiti, India) have been identified. Eight of these are new: Trematopora minima, Ulrichostylus bhargavai, Ptilodictya exiliformis, Phaenopora ordinarius, Oanduellina himalayaica, Pesnastylus? vesiculosum, Ralfina? originalis and Pinocladia triangulata. The fossil record and facies analyses of the area investigated indicate shallow‐water conditions within the subtropical–tropical realm. The distribution pattern of fossils among the Ordovician/Silurian succession on the Northern Gondwana shelf and the influence of the Late Ordovician cooling phases on marine organisms are distinctive owing to a dramatic reduction in diversity globally. As far as the bryozoan taxa of Spiti are concerned, only one (Helopora fragilis) of the 29 species was recorded above the Ordovician/Silurian boundary. Observed bryozoan communities are very similar to faunas of Laurentia, the Baltic, Siberia and southern China of early–late Ordovician age.     

The oldest bryozoans of Baltoscandia from the lowermost Floian (Ordovician) of north-western Russia: two new rare,small and simple species of Revalotrypidae

We describe two new species of esthonioporate bryozoans, Revalotrypa inopinata sp. nov. and R. yugaensis sp. nov., from the Lower Ordovician, south-east of Lake Ladoga, north-western Russia. The colonies of the two species are very small and were extracted from limestone nodules found in the lower part of glauconitic sandstone in the Joa Member (lowermost Floian). Revalotrypa inopinata sp. nov. and R. yugaensis sp. nov. are the oldest known bryozoans from Baltoscandia. Study of the two species includes scanning electron microscopy (SEM) imaging and X-ray microtomography (micro-CT). The palaeogeographic distribution of the oldest known bryozoans from the Lower Ordovician and the advantages and disadvantages of micro-CT for the study of Palaeozoic bryozoans are discussed. The authorship of Revalotrypidae, which has been inconsistently allocated in the literature, is discussed.     

塔里木盆地奥陶系苔虫多样性演变

本文研究了塔里木盆地奥陶系苔虫的分布延限和演化规律。苔虫的演化分为四个阶段:第一阶段为鹰山组—一间房组中下部沉积期,苔虫多样性和丰度均很低;第二阶段为一间房组上部—吐木休克组沉积期,苔虫的多样性处在一种波动上升的状态;第三阶段包括良里塔格组良五段—良四段沉积期,苔虫多样性和丰度均有一定程度的增加,而且绝大部分属种在接下来的第四阶段都有出现;第四阶段在良里塔格组良三段—良一段沉积期,是苔虫总体多样性明显增长的时期,也是本区奥陶纪苔虫的重要辐射期。随后,展开苔虫的多样性分析的研究。研究发现塔里木盆地奥陶系苔虫的演化趋势与世界范围的演化趋势基本一致,说明是受苔虫宏演化规律控制的。     

BRYOZOAN MUD-MOUNDS FROM THE UPPER ORDOVICIAN JIFARAH (DJEFFARA) FORMATION OF TRIPOLITANIA, NORTH-WEST LIBYA

Abstract:  A bryozoan fauna from carbonate mud-mounds is described from subsurface well cores from the Upper Ordovician (Lower Ashgill) Jifarah (Djeffara) Formation of Tripolitania, north-west Libya. Among a diverse assemblage dominated by trepostomes, nine species of bryozoans are identified, including Jifarahpora libyensis gen. et sp. nov. Delicate and robust branching, encrusting and nodular bryozoan growth forms are all common. The bryozoan-rich limestones are mostly mudstones and wackestones, with bafflestone and floatstone textures, but the mounds apparently lack organic framework and microbial fabrics. Regional geophysical data indicate rapid thickness changes between wells, where mound complexes locally up to 100 m thick had limited topographic relief over the surrounding sea floor. The mounds formed in a high-latitude, cool-water carbonate belt that extended widely across the northern margin of Gondwana. Quaternary analogues from the Great Australian Bight suggest that these early Ashgill mounds may have developed in slope environments during an episode of glacial lowstand that preceded the late Ashgill, Hirnantian glacial event.     

Bryozoans as taphonomic engineers,with examples from the Upper Ordovician (Katian) of Midwestern North America

A combination of encrusting calcitic bryozoans and early seafloor dissolution of aragonitic shells recorded in the Cincinnatian Series of the upper Midwest of North America allowed the preservation of abundant moulds of mollusc fossils bioimmured beneath the attachment surfaces of the bryozoans. We here call this preservational process ‘bryoimmuration’, defined as a bryozoan‐mediated subset of bioimmuration. The bryozoans moulded very fine details of the mollusc shells, usually with more accuracy than inorganic sediment moulds. Most of the bryozoans are heterotrypid trepostomes with robust low‐Mg calcite skeletons. The molluscs are primarily bivalves, gastropods, nautiloids and monoplacophorans with their originally aragonitic shells now dissolved. Many of the encrusting bryozoans are so thin and broad that they give the illusion of calcitic mollusc shells clinging to the moulds. Some molluscs in the Cincinnatian, especially monoplacophorans and epifaunal bivalves, would be poorly known if they had not been bryoimmured. Unlike internal and external moulds in sediment, bryoimmured fossils could be transported and thus record aragonitic faunas in taphonomic assemblages (e.g. storm beds) in which they would otherwise be rare or absent. In addition, bryoimmurations of aragonitic shells often reveal the ecological succession of encrustation on the shells by exposing the earliest encrusters and borings that were later overgrown. Bryoimmuration was common during the Late Ordovician because the calcite sea at the time quickly dissolved aragonitic shells on the seafloor before final burial, and large calcitic bryozoans very commonly used molluscs as substrates. Bryoimmuration is an important taphonomic process for preserving aragonitic faunas, and it reveals critical information about sclerobiont palaeoecology. Several Cincinnatian mollusc holotypes are bryoimmured specimens. Bryozoans involved in bryoimmuration enhance the preservation of aragonitic fauna and thus act as taphonomic engineers.     

新疆晚奥陶世晚期管状体及其古植物学物意义

本文系统描述了产自我国新疆塔里木盆地晚奥陶世晚期的管状体,包括2属8种,其中一个新种。通过对比研究,本管状体组合与Burgess和Edwards(1991）的下组合相当。根据本组合的研究,对Burgess和Edwards的组合进行了补充,其组合由不同类型的光壁管、低分异度的内壁加厚管组成、未见外壁加厚管和丝状体,组合的时代从中奥陶世到早志留世（晚Llandovery)。根据植物学的对比研究,管状体主要产自Nematophytales Lang.