贵州新元古代到寒武纪早期特异埋藏后生生物群及其研究意义

贵州化石丰富,素有古生物王国之称,其中早期特异埋藏后生生物十分发育,由老至新有埃迪卡拉系的瓮安生物群、江口庙河生物群、寒武系第1统的小壳动物群、第2统下部的牛蹄塘生物群及中上部的杷榔动物群、第3统底部的凯里生物群。这些特异埋藏生物群与云南寒武系的澄江动物群、关山生物群及陕南埃迪卡拉系高家山生物群构成了我国早期后生生物的演化链,反映了从动物起源（瓮安生物群）、可疑多门类动物出现（江口庙河生物群）、动物骨骼化（高家山生物群）、生物矿化质和量的变化或骨骼动物爆发性辐射（小壳动物群）及海绵动物辐射（牛蹄塘生物群）再到动物主要门类出现的寒武纪大爆发（澄江动物群）、海洋生物多样化及生态复杂化（凯里生物群）的演化过程。     

寒武纪早期宽川铺生物群中圆管螺化石显微结构及显微谱学分析

陕南寒武系底部宽川铺组不仅保存了大量的小壳化石,还以磷酸盐化的方式立体保存了多种软躯体动物的胚胎和成体化石,为研究早期动物矿化模式、个体发育方式以及动物躯体构型的早期辐射过程提供了非常关键的信息。然而宽川铺生物群的研究大多聚焦于化石系统分类及亲缘关系探索,对生物群的沉积背景、埋藏过程和保存模式的分析甚少。本文以宽川铺生物群的核心产出层位——陕西省西乡县大河镇宽川铺组下部磷质碎屑灰岩为研究对象,对其中的一类管状化石圆管螺及其围岩进行了显微结构学和显微谱学综合分析,获得了化石显微结构和关键结构对应的元素、矿物成分等信息,讨论了管状化石圆管螺的埋藏过程和保存模式,并在此基础上对其生物学特征进行了初步探讨。该研究对理解宽川铺生物群的埋藏机制提供了新的线索。     

【专辑序言】动物起源和寒武纪大爆发——序 言

动物起源和寒武纪大爆发是生命史上重要的演化创新事件。为展示相关领域的最新进展, 特组织主题为“动物起源和寒武纪大爆发”的论文专辑。作为专辑序言, 本文概述了动物起源和寒武纪大爆发领域的科学意义和当前研究趋势, 并简要介绍了本专辑的内容。专辑包含了来自13个研究单位共42位作者的12篇论文, 包括特约综述论文1篇和研究论文11篇。专辑不仅评述了相关领域的现状和未来发展趋势, 也展示了我国学者在该领域取得的部分新进展。这些进展涉及华南和华北数个特异埋藏化石库, 比如埃迪卡拉纪石板滩生物群、寒武纪宽川铺生物群和寒武纪凯里生物群等, 并涵盖了海绵动物、刺细胞动物、腕足动物、三叶虫和双瓣壳类节肢动物以及分类位置尚不明确的疑难动物化石等诸多类群。     

寒武纪早期澄江生物群中受创伤的中间型始莱德利基三叶虫(Eoredlichia intermedia)

三叶虫是寒武纪海洋中的常见动物,其受伤愈合现象的化石记录可以反映生态系统内物种之间竞争关系。中国华南寒武纪早期澄江化石生物群因保存软躯体构造化石而成为研究寒武纪大爆发时期古海洋生态群落的绝佳窗口,然而,澄江生物群中三叶虫受伤愈合现象的化石至今未见报道。中间型始莱德利基虫(Eoredlichia intermedia Lu,1940)是澄江生物群的常见物种,也是我国寒武系第二个三叶虫化石带的标准带化石。在2 000余枚中间型始莱德利基虫标本中,发现两枚成体标本的头甲侧边缘、颊刺和胸甲肋节保存了不同程度的残缺。据此推测,Eoredlichia intermedia在生命活动过程中曾受到碎壳型捕食动物的攻击或其他伤害而形成伤口。伤口部位边缘加厚且光滑,显示了明显的愈合痕迹。这些特征表明始莱德利基虫在受到非致死的伤害后,具备自身修复损伤的能力。这是迄今所知最为古老的,也是在澄江生物群中首次发现的三叶虫受伤并且愈合的标本,反映了寒武纪第二世第三期底栖生态系统中碎壳型捕食者和三叶虫猎物之间的军备竞赛生态关系。     

寒武纪幸运期宽川铺生物群疑难化石装饰玲珑球发育生物学*

作为磷酸盐化特异埋藏微体化石库, 寒武纪宽川铺生物群保存了大量软躯体动物胚胎和成体、藻类和多门类小壳化石, 为理解寒武纪大爆发初期的生物圈提供了重要的埋藏窗口。但前人的研究主要聚焦以橄榄蛋(Olivooides)为代表的刺细胞动物和以始祖动吻虫(Eokinorhynchus)等蠕虫为代表的蜕皮动物化石, 对化石库中大量疑难类群的探索尚有不足。本文报道了宽川铺生物群中一类新发现的疑难化石装饰玲珑球Linglongsphaera ornata n. gen. n. sp.。装饰玲珑球整体呈球状, 直径在544—1088 μm之间, 表面具瘤状突起装饰, 内部由平均直径24 μm的细胞组成。处于不同发育阶段的装饰玲珑球发育有8到180余个数量不等的腔室, 单个腔室的体积随着腔室数量的增长先增加而后减小, 分布的位置也从周缘直至布满整个内部, 最终腔室总体积占个体总体积的36%左右后保持稳定。根据现有证据, 笔者推测装饰玲珑球可能代表了一类已经灭绝的具有多细胞发育阶段的真核生物, 可能与某些多细胞藻类有较近的亲缘关系, 但具体的系统分类位置仍然不明。该研究为理解宽川铺生物群化石组合面貌和寒武纪大爆发初期生物圈的组成提供了新的线索。     

陕南寒武系底部宽川铺组微体化石人工智能识别

我国陕南寒武纪初期的宽川铺组(距今大约535百万年)以盛产磷酸盐化的微体小壳化石和球状动物胚胎化石而闻名于世,是探索早期动物门类起源和寒武纪生命大爆发研究中的一个非常重要的窗口。在宽川铺组中寻找微体化石新类型主要依赖显微镜下人工挑选的传统方法日趋低效,迫切需要新的技术手段来解决这些问题。而微体化石数量庞大,大小接近,形态简单,非常适合于采用机器学习的手段进行人工智能分类。我们在宽川铺组微体化石中尝试使用机器学习的手段来进行化石图像识别和机器分拣。采用方向梯度直方图来提取化石图像的主要向量特征,并设计了二叉树型多分类识别器进行化石数字分类。目前处理了5 000多张微体化石照片的人工智能识别,已经取得了较高的准确率。     

动物的起源和寒武纪大爆发：来自中国的化石证据北大核心

近30年来,中国埃迪卡拉纪—寒武纪发现了包括瓮安生物群和澄江动物群在内一系列重要化石群,为揭示动物的起源和寒武纪大爆发过程提供了全球独一无二的古生物学证据。文中全面而简洁地介绍发现于华南埃迪卡拉纪—寒武纪的所有化石群和重要动物化石发现,总结其中特异化石群保存类型和埋藏环境。其中,陡山沱型磷酸盐化胚胎化石群、庙河型宏体碳质膜化石群和牛蹄塘型海绵动物群,以及陡山沱组硅化的动物休眠胚胎化石和宽川铺动物群中"rsten"型化石均是全球这一时期华南独有的特异埋藏化石群。从时空两方面对化石群进行综合分析认为,动物可靠的最早化石记录发现于埃迪卡拉纪早期,成冰纪及其以前的动物化石均存在疑问。动物的起源和寒武纪大爆发经历了从浅水逐步向深水迁移,以及阶段性辐射和灭绝的过程。首先动物经历了在埃迪卡拉纪早期的隐形微体动物早期演化阶段,之后经过以埃迪卡拉型生物为代表的大型复杂化演化阶段,在寒武纪初期发生以梅树村动物群为代表的两侧对称动物和生物骨骼矿化的大爆发,并随后又被以澄江动物群为代表的寒武纪动物群所替代,在筇竹寺期达到了动物造型和生态系统复杂化的高峰。     

动物的起源和寒武纪大爆发:来自中国的化石证据

近30年来,中国埃迪卡拉纪—寒武纪发现了包括瓮安生物群和澄江动物群在内一系列重要化石群,为揭示动物的起源和寒武纪大爆发过程提供了全球独一无二的古生物学证据。文中全面而简洁地介绍发现于华南埃迪卡拉纪—寒武纪的所有化石群和重要动物化石发现,总结其中特异化石群保存类型和埋藏环境。其中,陡山沱型磷酸盐化胚胎化石群、庙河型宏体碳质膜化石群和牛蹄塘型海绵动物群,以及陡山沱组硅化的动物休眠胚胎化石和宽川铺动物群中"rsten"型化石均是全球这一时期华南独有的特异埋藏化石群。从时空两方面对化石群进行综合分析认为,动物可靠的最早化石记录发现于埃迪卡拉纪早期,成冰纪及其以前的动物化石均存在疑问。动物的起源和寒武纪大爆发经历了从浅水逐步向深水迁移,以及阶段性辐射和灭绝的过程。首先动物经历了在埃迪卡拉纪早期的隐形微体动物早期演化阶段,之后经过以埃迪卡拉型生物为代表的大型复杂化演化阶段,在寒武纪初期发生以梅树村动物群为代表的两侧对称动物和生物骨骼矿化的大爆发,并随后又被以澄江动物群为代表的寒武纪动物群所替代,在筇竹寺期达到了动物造型和生态系统复杂化的高峰。     

寒武纪大爆发——来自贵州的化石证据*

寒武纪展示了生物演化和生态创新最为关键的一段历史, 在此期间发生了后生动物快速的辐射性演化事件, 被称为“寒武纪大爆发”。近四十年来, 基于寒武纪特异埋藏生物群的大量研究为解密寒武纪大爆发具体过程、主要动物类群起源与生态演化作出了重要贡献。贵州素有古生物王国之称, 在寒武系地层中不仅保存了大量解剖学细节精美的化石资源, 也在多个地区产出时间连续的生物组合演化序列, 在探讨动物起源与演化、全球地层对比及群落古生态学等方面具有极其重要的科研价值。近年来, 以小壳动物群、牛蹄塘生物群、杷榔生物群、剑河生物群、凯里生物群等多个生物群在贵州的发现提供了早期后生生物的新信息, 加密了中国乃至全球早期后生生物特异埋藏化石群的演化链, 为全面揭示寒武纪生物群落面貌、早期多门类后生动物的辐射演化和海洋生物群落演替提供了独特的意义, 最终为深入解读寒武纪大爆发的过程与发生机制提供重要实证。本文简要总结了贵州地区在该领域的主要学术贡献, 结合全球研究进展, 对目前存在的问题和未来研究方向提出展望。     

陕南早寒武世早期Quadrapyrgites再研究

处于"寒武纪生命大爆发"序幕阶段的梅树村期,生物类群大规模辐射,身体构型快速革新,与前寒武纪生物群面貌明显不同.最近在陕南宁强宽川铺地区梅树村期地层中发现了大量五辐射Punctatus及部分四辐射四方塔形壳属Quadrapyrgites,其中包括1个新种Quadrnpyrgites undulatuscostalis sp.nov..在此基础上对Quadrapyrgites进行了属征补充.双胚层腔肠动物的出现标志着地球生命史的真后生动物演化开端,在生物起源演化历程上占据着关键的位置.本文为研究真后生动物起源演化、生物辐射、体型构建提供了重要实证.     

陕南早寒武世宽川铺生物群沉积环境及埋藏机制研究

陕南早寒武世宽川铺生物群三维立体保存了大量结构精美的磷酸盐化胚胎及小壳化石,为后生动物演化及化石胚胎学的研究提供了珍贵的实证材料。目前的研究主要集中在化石分类学及演化生物学上,而对沉积环境及埋藏机制的研究却很少涉及。文中通过对大量野外岩石照片、岩石薄片、小壳化石SEM照片的综合研究后认为,宽川铺生物群不是原地埋藏的产物,而是事件沉积的结果。该研究对于探讨宽川铺生物群化石的埋藏环境及保存机制具有一定的意义。     

关山生物群中始海百合化石的再研究*

关山生物群是继澄江生物群之后云南寒武纪早期地层中发现的又一个特异埋藏的化石宝库。现已报道10多个门类的化石动物,对研究寒武纪生命大爆发、后生动物起源及演化、寒武纪早期生态系统的复原等重大学术问题具有特殊的意义。始海百合属于棘皮动物门海蕾亚门,于寒武纪早期出现,志留纪灭绝。笔者将荧光显微镜等先进成像方式与传统的研究手段相结合,对新采集到的关山生物群始海百合化石标本进行深入细致的系统古生物学研究,对其精细形态学构造和生活习性获得更深入的了解。这对于认识寒武纪早期的生物多样性和棘皮动物的演化都具有重要的意义。     

埃迪卡拉纪至寒武纪苗岭世刺细胞动物化石研究现状与展望

刺细胞动物是一类具有刺细胞的水生无脊椎动物,分布在世界各地的海洋和淡水中.作为后生动物最早分化出的一支,刺细胞动物对研究后生动物的起源和早期演化具有极其重要的意义,也为研究后生动物系统发育、地层对比和古地理恢复等方面提供了重要的科研线索.本文简要介绍了刺细胞动物早期(埃迪卡拉纪至寒武纪苗岭世)的化石记录和研究现状,将刺...     

Diverse radial symmetry among the Cambrian Fortunian fossil embryos from northern Sichuan and southern Shaanxi provinces,South China

The Cambrian Fortunian fossil embryos exhibit embryonic development of ancient animals and hence have important bearings on evolutionary developmental biology. They have radial symmetry, and may be early representatives of cnidarians. Here we report new material of three-dimensionally phosphatized fossil embryos from the Fortunian Kuanchuanpu Formation and coeval strata in northern Sichuan and southern Shaanxi provinces, South China. The new material includes previously reported fossil embryos assignable to Pseudooides prima with biradial symmetry or pseudo-hexaradial symmetry, Quadrapyrgites quadratacris with tetraradial symmetry, and Olivooides multisulcatus with pentaradial symmetry. Additionally, we recovered two new types of fossil embryos, i.e., Embryo I with hexaradial symmetry and Embryo II with octaradial symmetry, and they are tentatively suggested to represent new cnidarians. In contrast to the diverse radial symmetry of the Fortunian cnidarians, modern cnidarians exhibit stable tetraradial symmetry in medusozoans, biradial symmetry in anthozoans, and bilateral symmetry in siphonophores (Hydrozoa). The current study supports the view that the tetraradial symmetry of modern medusozoans is a surviving remnant of their Fortunian relatives.     

Origin and early diversification of the phylum Cnidaria Verrill: major developments in the analysis of the taxon's Proterozoic–Cambrian history

Diploblastic eumetazoans of the phylum Cnidaria originated during the Neoproterozoic Era, possibly during the Cryogenian Period. The oldest known fossil cnidarians occur in strata of Ediacaran age and consist of polypoid forms that were either nonbiomineralizing or weakly so. The oldest possible anthozoans, including the genus Ramitubus, may be related to tabulate corals and occur in the Doushantuo Lagerstätte (upper Doushantuo Formation, South China), the age of which is poorly constrained (approximately 585 Ma?). Conulariid scyphozoans may first appear as early as 635–577 Ma (Lantian Formation, South China). A definite conulariid, most similar to Palaeozoic species assigned to the genus Paraconularia, occurs in association with the possible scyphozoan, Corumbella werneri, in the latest Ediacaran (c. 543 Ma) Tamengo Formation of Brazil. Basal Cambrian (c. 540 Ma) phosphorites in the upper Kuanchuanpu Formation (South China) yield solitary polyps of the oldest probable anthozoan (Eolympia pediculata), which appears to have been a stem hexacorallian. This same formation contains fossils interpreted by some authors as pentaradial cubozoan polyps; however, both the oldest known cubozoans and the oldest hydrozoans, all medusae, may actually occur in the Cambrian (Series 3, c. 505 Ma) Marjum Formation (Utah, USA). Although these recently published palaeontological data tend to corroborate the hypothesis that Cnidaria has a relatively deep Neoproterozoic history, the timing of major internal branching events remains poorly constrained, with, for example, the results of some molecular clock analyses indicating that the two cnidarian subphyla (Anthozoaria and Medusozoa) may have originated as many as one billion years ago. Further progress towards elucidating the evolution and early fossil record of cnidarians may accrue from: (1) an intensive search for phosphatized soft parts in possible anthozoans from the Ediacaran Doushantuo Formation; (2) an expanded search for Ediacaran conulariids; and (3) additional detailed analyses of the taphonomy and preservation of Ediacaran and Cambrian cnidarians, including possible pentaradial cubozoan polyps from the Fortunian upper Kuanchuanpu Formation.     

寒武纪早期岩家河生物群:研究进展和展望*

埃迪卡拉纪-寒武纪转换时期动物的起源、演化和"寒武纪大爆发"一直是国际古生物学界研究的热点问题,其中寒武纪早期小壳化石群与埃迪卡拉纪化石群和寒武纪早期澄江化石库之间的内在关系是古生物学界研究的难题,其主要原因是寒武纪早期与小壳化石群伴生的宏体动、植物化石的缺乏。发现于峡东地区的寒武纪早期岩家河生物群填补了这一缺失环节,该生物群包含宏体动物、宏观藻类、小壳化石、球形化石(可能的胚胎化石)、微古植物和蓝菌类等化石,部分宏体化石显示了从埃迪卡拉纪向寒武纪过渡色彩。化石保存方式有碳质膜、黄铁矿化、磷酸盐化、硅化。因此对岩家河生物群生物多样性和埋藏学进行综合研究,将可提供纽芬兰世(梅树村期)碳酸盐台地—碳酸盐台地内部的局部凹陷盆地相的一个较完整的生物景观图,对探索"寒武纪大爆发主幕"前夕生物的辐射、演化模式及保存机制具有重要的科学意义。     

Eyes and vision in the Chengjiang arthropod Isoxys indicating adaptation to habitat

Schoenemann, B. & Clarkson, E.N.K. 2011: Eyes and vision in the Chengjiang arthropod Isoxys indicating adaptation to habitat. Lethaia, Vol. 44, pp. 223–230. The arthropod Isoxys is common in the lower Cambrian Chengjiang biota, but only a few specimens retain details of the eye structure, though the eyes are invariably flattened. One specimen of Isoxys auritus has a pair of large eyes, projecting from the body and showing a flexible eye‐stalk, a discoidal, slightly convex palpebral lobe, and part of the original visual surface upon which lenses can be distinguished. The remarkable preservation allows the eye parameter, sensitivity, and the anatomical acuity of this eye to be established; it was adapted to an environment where the illumination corresponds to that of street light at night, in other words up to ～140 metres depth. This fits well with previous estimates. A second specimen, from a different locality (Mafang), interpreted as a different form, probably a different species, was adapted to more shallow, well‐lit surface waters. □Arthropoda, Cambrian, Chengjiang, ecological niche, Isoxys, vision.     

A new scyphozoan from the Cambrian Fortunian Stage of South China

Animals with radial symmetry are abundant in the Cambrian Fortunian Stage of South China, but with relatively low diversity: representatives include Olivooides, Quadrapyrgites, carinachitiids, hexangulaconulariids and Pseudooides. Here, we report a new radial animal, Qinscyphus necopinus gen. et sp. nov., from the Fortunian small shelly fauna of southern Shaanxi Province, South China. Qinscyphus necopinus has a cup‐shaped profile, with slightly raised annuli and five groups of triangular thickenings in pentaradial symmetry. This organism has a comparable morphology to, and thus a close affinity with, Olivooides and Quadrapyrgites, and is interpreted as a coronate scyphozoan. This discovery adds a new crown‐group cnidarian to the Cambrian Explosion.     

A new early Cambrian bivalved euarthropod from Yunnan,China and general interspecific morphological and size variations in Cambrian hymenocarines

The hymenocarines were a major and diverse group of euarthropods featured by a bivalved head carapace and a segmented trunk comprising tergo-pleural rings notably from the Cambrian Burgess Shale-type Lagerstätten. Here we document a new ~50 mm long hymenocarine Xiazhuangocaris chenggongensis n. gen. n. sp. from the Xiazhuang fossil assemblage, a slightly younger occurrence of the Chengjiang Lagerstätte within the lower Cambrian Hongjingshao Formation (Cambrian Series 2, Stage 3) in Chenggong, Yunnan, southwestern China. X. chenggongensis is characterized by the bivalved carapace with each valve bearing a protruded anterior tip and a prominent posterior notch, which resembles the P-element of the radiodont Hurdia and is unique among the hymenocarines. The trunk consists of at least 13 tergo-pleural rings including presumably eight abdominal ones terminating in a pair of ovate caudal rami. With the body organization and morphological features closest to waptiids, X. chenggongensis represents a ‘larger’ waptiid-like hymenocarine. The morphometric analysis recognizes the family-level groupings of Cambrian hymenocarines based on the number of tergo-pleural rings and the proportion of exposed trunk length, indicating that these are useful characters for studying hymenocarine morphology and phylogeny. Cambrian hymenocarines exhibited great interspecific body size variations even between sister species of the same family, further suggesting that niche diversification happened on the family level and even among phylogenetically close genera or species during the Cambrian explosion.