The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma,Itajaí Basin,Brazil)

The Avalon biota (Ediacaran Period, 570–559 Ma) marks the first appearance of macroscopic and complex benthic communities in the fossil record. This assemblage is known from a few localities worldwide, mainly in Canada and England. Here, we report for the first time the presence of Ediacaran macrofossils in deposits of similar age from Gondwana (Itajaí Basin, southern Brazil). Our new radiometric date (~563 Ma) indicates that the Itajaí Basin can be chronocorrelated with the classic Avalonian deposits and thus represents one of the oldest records of the Ediacaran biota in Gondwana. We describe the presence of the Ediacaran genus Palaeopascichnus, as well as discs (Aspidella and Nimbia), and other problematic forms. Contrary to the deep-marine macroorganisms of the Avalon Assemblage, the Itajaí fossils are associated with abundant and exceptionally preserved three-dimensional microbial mats and microbially induced sedimentary structures (MISS) in relatively shallow settings (upper slope and distal delta front deposits). In this sense, the Itajaí biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later White Sea Assemblage.     

Glaciation and ~ 770 Ma Ediacara (?) Fossils from the Lesser Karatau Microcontinent,Kazakhstan

The Cambrian explosion, c. 530–515 Ma heralded the arrival of a diverse assembly of multicellular life including the first hard-shelled organisms. Fossils found in Cambrian strata represent the ancestors of most modern animal phyla. In contrast to the apparent explosiveness seen in the Cambrian fossil record, studies of molecular biology hint that the diversification observed in Cambrian strata was rooted in ancestry extending back into the Ediacaran (635–542 Ma). Fossil evidence for this mostly cryptic phase of evolution is derived from the soft-bodied fossils of the Ediacaran biota found throughout the world and bilaterian embryos found in the Doushantuo lagerstätte in South China. The first appearance of Ediacara fauna is thought to have followed the last of the ~ 750–635 Ma Neoproterozoic glacial episodes by 20–30 million years. In this paper, we present evidence for the oldest discovery of the ‘Ediacara’ discoidal fossils Nimbia occlusa and Aspidella terranovica (?) that predate the early Cryogenian glaciations by more than fifty million years. There is considerable disagreement over the significance of discoidal Ediacaran fossils, but our findings may support earlier suggestions that metazoan life has roots extending deeper into the Proterozoic Eon. We also confirm the presence of a Late Cryogenian (e.g. “Marinoan”) glaciation on the Lesser Karatau microcontinent including dropstones and striated clasts within the glacial strata.     

Remarkable preservation of microbial mats in Neoproterozoic siliciclastic settings: Implications for Ediacaran taphonomic models

It is beyond doubt that the appearance of infaunal bioturbation and metazoan biomineralization across the Ediacaran–Cambrian transition irreversibly affected the nature of marine sediment architecture and biogeochemistry. Here we review those changes in relation to their likely effect upon the processes of fossil preservation, especially within siliciclastic sediments. Processes of soft-tissue preservation in siliciclastic settings from the Ediacaran Period, including microbes and microbial mats as well as Ediacaran macrofossils, are here reviewed within this context. Highlighted examples include the exceptional preservation of microbes found in association with wrinkle structures and Ediacaran macrofossils in England and Newfoundland (replicated by silicate minerals) and in the White Sea region of Russia (replicated by iron sulphide). These occurrences show that soft-tissue preservation in siliciclastic settings went well beyond that typical for Ediacaran macrofossils alone and also extended to similar modes of preservation in associated microbes. Using these new observations it can be argued that several existing explanations for Ediacaran fossil preservation can be united within a biogeochemical model that involves evolution of the sediment mixed layer across this transition.     

Revisiting the Charnian Supergroup: new advances in understanding old rocks

More than two centuries of study have culminated in work that promises to re-write large parts of the stratigraphy, mode of origin, palaeontology, age and structure of the late Precambrian to early Cambrian 'basement' rocks in Charnwood Forest, UK.     

Rapid changes of magnetic Field polarity in the late Ediacaran: Linking the Cambrian evolutionary radiation and increased UV-B radiation

Novelty in the biological world is the culmination of genetic changes often triggered by the physical environment. The most radical phase of biological evolution took place during the Cambrian Evolutionary Radiation (CER). Prior to the CER, bacterial matgrounds and associated communities of Ediacaran organisms dominated the shallow seafloor. Near the end of the Ediacaran Period, ~ 550 million years ago, many soft-bodied biota went extinct. In the Early Cambrian, animals with the ability to burrow vertically altered the ecology of the seafloor and biomineralization became commonplace. Here we link the terminal Ediacaran extinction, the Cambrian substrate revolution and the diversification of biomineralizing organisms to changes associated with the reversal frequency of the Earth's magnetic field. Beginning around 550 Ma and continuing through much of the Cambrian, the Earth's magnetic field was rapidly reversing. Models, and limited paleointensity studies, indicate that rapid reversals are a feature of an overall weaker dipole. A weakened dipole reduces the dimensions of the magnetosphere that provides a barrier to incoming cosmic radiation. Here we show that the environmental effects of that collapse include increased dosing of UVB radiation into the shallow marine environment. Increased UVB radiation in the shallow marine environment provided selective pressure favoring organisms that could detect and avoid UVB damage by burrowing vertically, moving up or down in the water column, growing protective shells and other ‘flight from light’ mechanisms. These changes took place in advance of the CER, but effectively cleared the ecological space for the subsequent changes in the later Cambrian.     

Aspects of magmatism and plate tectonics in the Precambrian of England and Wales

The geological features of igneous, metamorphic and sedimentary rocks comprising the Precambrian of England and Wales suggest formation in one or more Precambrian orogenic cycles. They are now interpreted in terms of plate tectonics. Evidence for Late Proterozoic plate subduction in the Mona Complex of Anglesey is suggested by the association of pillow lavas, cherts, high P/T metamorphic rocks and by the occurrence of gabbros and serpentinites with similar features to rocks believed to comprise the oceanic crust. Precambrian rocks in England and South Wales include calc-alkaline plutonic complexes (Malvern and Johnston Complexes), calc-alkaline lavas (Uriconian and Charnian) and basic and intermediate intrusions of tholeiitic affinity (dykes in the plutonic complexes and granophyric diorites in Charnwood Forest). The features of these rocks indicate formation in a continental margin setting and this is consistent with features of the Rushton Schist and Primrose Hill “gneiss” which suggest that they predate the Late Proterozoic orogenic activity. This evidence is consistent with plate tectonic models involving oceanic plate subduction below the Mona Complex from an ocean to the northwest, or from a small ocean basin southeast of the complex. The Warren House lavas show some affinities to ocean floor basalts and are problematic with regard to the Precambrian history of the area.     

The anomalous Ca cycle in the Ediacaran ocean: Evidence from Ca isotopes preserved in carbonates in the Three Gorges area,South China

The Ediacaran–Cambrian was one of the most important periods for the evolution of life. Recent studies have provided detailed chemostratigraphies that decipher the linkages between ambient surface environmental changes and biological evolution. The occurrence of skeletal fossils in Ediacaran rocks suggests that the possible onset of Ca-biomineralization started in the latest Neoproterozoic. Molecular clocks also predict the emergence of animals containing Ca-carbonate spicules in the Neoproterozoic. Therefore, it is important to estimate the transition of the Ca cycle in seawater. Ancient Ca cycles in the oceans are estimated from the calcium isotopic compositions of carbonate rocks. However, the lack of continuous Ca isotopic data in the Ediacaran leaves the Ca cycle unresolved.The almost continuously exposed, Ediacaran and Cambrian strata in South China mainly comprise carbonate rocks with subordinate black shales and sandstones, which contain many fossils, suitable for the study of environmental and biological changes. We conducted drilling from the Liantuo, via the Nantuo, Doushantuo, Dengying and Yanjiahe to the Shuijingtuo formation at four sites in the Three Gorges area in order to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed ⁴⁴Ca/⁴²Ca ratios in carbonate rocks with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) screened for diagenetic alteration.The resultant δ^44/42Ca ratios exhibit a smooth curve. The values of δ^44/42Ca are anomalously high relative to those in the Phanerozoic, and they gradually decrease towards the end of the Ediacaran. Our new Ca isotope chemostratigraphy suggests that a different Ca cycle had existed during the Ediacaran. The long-term, high δ^44/42Ca is not simply explicable by changes in temperature, differences in carbonate mineralogy, or changes in the input/output fluxes of Ca to the ocean. We propose three possible explanations for the observed high δ^44/42Ca ratios in the Ediacaran: high δ^44/42Ca ratios of Ca inputs, potential undiscovered sinks of Ca with low δ^44/42Ca values, and negligible isotope fractionation between carbonate and seawater; we consider that one or all of these contributed to the high δ^44/42Ca ratios. Of these, we prefer the small isotope fractionation, which implies that the Ca concentration in seawater was initially low in the early Ediacaran and increased throughout that period.     

The Cambrian Explosion: Plume-driven birth of the second ecosystem on Earth

The birth of modern life on Earth can be linked to the adequate supply of nutrients into the oceans. In this paper, we evaluate the relative supply of nutrients into the ocean. These nutrients entered the ocean through myriad passageways, but primarily through accelerated erosion due to uplift. In the ‘second ecosystem’, uplift is associated with plume-generation during the breakup of the Rodinia supercontinent. Although the evidence is somewhat cryptic, it appears that the second ecosystem included the demospongia back into the Cryogenian (~ 750 Ma). During the Ediacaran–Cambrian interval, convergent margin magmatism, arc volcanism and the closure of ocean basins provided a second pulse of nutrient delivery into the marine environment. A major radiation of life forms begins around 580 Ma and is represented by the diverse and somewhat enigmatic Ediacaran fauna followed by the Cambrian Explosion of modern phyla during the 540–520 Ma interval. Tectonically, the Ediacaran–Cambrian time interval is dominated by the formation of ultra-high pressure (UHP), high pressure (HP) and ultra-high temperature (UHT) orogenic belts during Gondwana orogenesis. Erosion of this extensive mountainous region delivered vast nutrients into the ocean and enhanced the explosiveness of the Cambrian radiation. The timing of final collisional orogeny and construction of the mountain belts in many of the Gondwana-forming orogens, particularly some of those in the central and eastern belts, post-date the first appearance of modern life forms. We therefore postulate that a more effective nutrient supply for the Cambrian radiation was facilitated by plume-driven uplift of TTG crust, subsequent rifting, and subduction-related nutrient systems prior to the assembly of Gondwana. In the outlined scenario, we propose that the birth of the ‘second ecosystem’ on our planet is plume-driven.     

Evolution of the Ediacaran Doushantuoian Meta-Paleo-Community in Northeast Guizhou, South China

Macroscopic organisms lived in the Yangtze Sea of South China during the Late Doushantuo period of the Ediacaran. The results of the specimen collections and statistics within each meter show that the macroscopic biota from the Ediacaran Doushantuo Formation in northeast Guizhou, South China, can be subdivided into Globusphyton, Cucullus, Sectoralga–Longifuniculum, Beltanelliformis, and Baculiphyca–Gesinella paleo-communities. The paleo-community evolution indicates the relationship not only between biota and environment, but also between metaphytes and metazoans. From the Globusphyton paleo-community, through to the Sectoralga–Longifuniculum paleo-community, to the Cucullus paleo-community, the increase in the abundance and diversity of metaphytes (especially the branching macroalgae) and metazoans implies that the oxygen content in the seawater increased gradually. Both the Beltanelliformis and Baculiphyca–Gesinella paleo-communities could be related to a deteriorated environment and fragile ecosystem. The emergence, abundance, and diversity of macroscopic metaphytes, which were closely connected with the environmental microchanges, accelerated the process, improving the environment and increasing oxygen, and established an important platform for the development of macroscopic metazoans.     

Main stages of tectonomagmatic activity of the Tuva–Mongolian microcontinent in the Precambrian: data on the U–Pb age of zircons

The U–Pb age of zircons from Ediacaran sandstones of the cover of the Tuva–Mongolian microcontinent and the rocks of its Early Precambrian basement (Gargan block) was analyzed by the LA–ICP–MS method. The major stages of tectonomagmatic activity of this block include the Neoarchean, Paleoproterozoic (no younger than 2 Ga), and Neoproterozoic. Comparison of the age of zircons from Ediacaran terrigenous rocks of the Tuva–Mongolian microcontinent and sandstones of the reference sections of the Ediacaran shelf of the Siberian platform undeniably indicates their independent accumulation.     

Birth and early evolution of metazoans

The reconstruction of the phylogenetic tree of animals (TOA) has long been one of the central interests in biological and paleobiological sciences. We review the latest results of paleontological and stratigraphical studies on the Ediacaran–Cambrian sequences mainly from South China for revising the TOA in accordance with modern genome biology. A particular focus is given to the pattern of animal diversification based on the fossil first appearances of high-rank clades chiefly in phylum-level. The results show an abrupt divergence of lineages during the Ediacaran–Cambrian transition; however, the appearances of metazoan phyla were obviously diachronous, with three major phases recognized herein. The first phase is marked by the appearances of basal metazoan phyla in the latest Ediacaran. Very few unequivocal bilaterian clades were present at this phase. The second phase occurred in the Terreneuvian (Cambrian Stages 1–2), represented by the occurrences of many lophotrochozoan lineages. This phase also involves the appearances of calcified basal metazoan lineages, and possibly, those of contentious ecdysozoans in the latest Terreneuvian, but no deuterostome has been known from this age. The third and also the largest phase occurred in the Cambrian Stage 3, which involve all the three supraphylogenetic clades of the Eubilateria. A number of lophotrochozoan lineages, the bulk of ecdysozoans, and all deuterostome phyla, appeared for the first time in this phase. Since there is no unambiguous evidence for bilaterians in the Ediacaran, the Cambrian explosion sensu stricto was an abrupt diversification of bilateral lineages in a short time of ca. 25 million years across the Ediacaran–Cambrian boundary. Next critical issues in research include high-resolution chrono- and chemostratigraphic analyses, correlations between biotic events and environmental perturbations, physiological approach to the biological connotation of biomineralization, and exploration for the lost mid-oceanic biota and environments, which are crucial in understanding the entire picture of the Cambrian explosion.     

The role of spatial heterogeneity of the environment in soil fauna recovery after fires

Forest fires are almost always heterogeneous, leaving less-disturbed sites that are potentially suitable as habitats for soil-dwelling creatures. The recovery of large soil animal communities after fires is therefore dependent on the spatial structure of the burned habitats. The role of locally less disturbed sites in the survival of soil macrofauna communities along with traditionally considered immigration from the surrounding undisturbed habitats is shown by the example of burnt areas located in three geographically distant regions of European Russia. Such unburned soil cover sites (perfugia) occupy 5–10% of the total burned habitats. Initially, perfugia are characterized by much higher (200–300% of the average across a burned area) diversity and abundance of soil fauna. A geostatistical method made it possible to estimate the perfugia size for soil macrofauna at 3–8 m.     

Field and laboratory tests for recognition of Ediacaran paleosols

Not a single paleosol had been described from rocks of Ediacaran age until 2011, but 354 Ediacaran paleosols have been described by 20 different authors since then. Some of these newly recognized paleosols have proven controversial, so this paper reviews 20 distinct tests to determine whether a particular Ediacaran bed could be a paleosol, or not. One problem has been that Ediacaran paleosols are not precisely like modern soils because they lack root traces, a diagnostic feature of Silurian and geologically younger paleosols. The principal problem for recognition of some Ediacaran paleosols is the occurrence in them of megafossils assumed to have been marine, although most of these fossils remain problematic for both biological and ecological affinities. Not all the tests discussed here are diagnostic of paleosols, some are ranked permissive or persuasive. Permissive conditions for paleosols include ripple marks, hummocky bedding, pyritic limestones, acritarchs or thalloid fossils, low strontium isotopic ratios, high δ²⁶Mg ratios, and red color. Persuasive tests include loessites, tsunamites, desert playa minerals, low boron content, high δ¹⁰B isotopic ratios, high carbon/sulfur ratios, and very low total/reactive iron ratios. Diagnostic tests include matrix-supported lapilli or crystal tuff parent materials, ice wedges and other cryoturbation, sepic birefringence fabrics, evaporitic sand crystals, and negative geochemical strain and mass transfer, and highly correlated δ¹³C and δ¹⁸O. Like other geological periods, the Ediacaran is known from a variety of marine and non-marine paleoenvironments     

The end of the Ediacara biota: Extinction,biotic replacement,or Cheshire Cat?

The Ediacaran–Cambrian transition signals a drastic change in both diversity and ecosystem construction. The Ediacara biota (consisting of various metazoan stem lineages in addition to extinct eukaryotic clades) disappears, and is replaced by more familiar Cambrian and Paleozoic metazoan groups. Although metazoans are present in the Ediacaran, their ecological contribution is dwarfed by Ediacaran-type clades of uncertain phylogenetic affinities, while Ediacaran-type morphologies are virtually non-existent in younger assemblages. Three alternative hypotheses have been advanced to explain this dramatic change at, or near, the Ediacaran–Cambrian boundary: 1) mass extinction of most Ediacaran forms; 2) biotic replacement, with early Cambrian organisms eliminating Ediacaran forms; and 3) a Cheshire Cat model, with Ediacaran forms gradually disappearing from the fossil record (but not necessarily going extinct) as a result of the elimination of unique preservational settings, primarily microbial matgrounds, that dominated the Ediacaran. To evaluate these proposed explanations for the biotic changes observed at the Ediacaran–Cambrian transition, environmental drivers leading to global mass extinction are compared to biological factors such as predation and ecosystem engineering. We explore temporal and biogeographic distributions of Ediacaran taxa combined with evaluations of functional guild ranges throughout the Ediacaran. The paucity of temporally-resolved localities with diverse Ediacaran assemblages, combined with difficulties associated with differences in taphonomic regimes before, during, and after the transition hinders this evaluation. Nonetheless, the demonstration of geographic and niche range changes offers a novel means of assessing the downfall of Ediacara-type taxa at the hands of emerging metazoans, which we hypothesize to be most likely due to the indirect ecological impact metazoans had upon the Ediacarans. Ultimately, the combination of studies on ecosystem construction, biostratigraphy, and biogeography showcases the magnitude of the transition at the Ediacaran–Cambrian boundary.     

Ediacaran in Uruguay: Facts and controversies

The Ediacaran of Uruguay has been regarded as containing a significant geological and paleontological record, which would make these successions critical to unraveling diverse aspects regarding the assembly of southwestern Gondwana and to understanding the conditions surrounding the rise of animal life in a period punctuated by drastic paleoenvironmental changes. However, a review of currently available data leads to the conclusion that, although variable, the stratigraphy, distribution and age of these units remain ambiguous. The same is true for existing basin models and tectonic evolution, which show different and sometimes contradicting supporting evidence. Here, we propose that the Ediacaran record consists of the Maldonado Group (Playa Hermosa, Las Ventanas and San Carlos formations), and the Tacuarí, Barriga Negra, Rocha and Sierra de Aguirre formations. The Arroyo del Soldado Group (Yerbal, Polanco Limestones and Cerro Espuelitas formations) and the Arroyo de la Pedrera Group (Piedras de Afilar and Cerro Victoria formations) were likely deposited between 700 and 1000 Ma. The best available radiometric age constraints indicate intense magmatic–tectonic activity occurred between 600 and 560 Ma, incompatible with previous models suggesting a stable, Atlantic-type passive margin on this portion of southwestern Gondwana. Further research is needed in order to firmly establish a consistent litho- and chronostratigraphic framework; particularly, before attempting any regional or global correlation, and inferences on global paleoenvironmental and paleobiological events.     

瓮安生物群中后生动物化石研究进展及问题讨论

贵州瓮安埃迪卡拉（震旦）纪陡山沱期磷酸盐化生物群具有生物多样性特征，包含有蓝菌、多细胞藻类、疑源类、后生动物休眠卵及胚胎、可疑的海绵动物、管状后生动物和微小两侧对称的后生动物等化石类型，是迄今为止全球保存最为完好的晚前寒武纪磷质化石库。瓮安陡山沱组磷质岩提供了早期生命从简单到复杂进化过程中的重要化石记录，展示了埃迪卡拉生物群出现以前早期多细胞生物的生命景观，为研究晚前寒武纪生物圈面貌提供了一个重要的埋葬学窗口。近来，通过醋酸浸解法，在贵州瓮安陡山沱期含磷地层中发现了大量疑似后生动物的实体化石（包含了所有已经报道的类型或与之相似的化石类型）新材料，为了解这些化石的内部构造特征，将一些化石包埋后制作了定向薄片。基于上述化石新材料，结合定向薄片的研究和前人的研究成果，本文详细介绍了瓮安生物群中后生动物化石研究的新进展和存在的问题。     

In-situ analyses of phosphorus contents of carbonate minerals: Reconstruction of phosphorus contents of seawater from the Ediacaran to early Cambrian

The Ediacaran and Cambrian periods were one of the most important periods for the evolution of life. The biodiversity drastically expanded in the period. However, the origins are still ambiguous because surface environmental changes through the time have not been well understood yet. We conducted in-situ analyses of the phosphorus contents of carbonate minerals with a laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) to estimate the phosphorus contents of seawater from the Ediacaran to the early Cambrian. Carbonate rocks contain not only the carbonate minerals but also detrital and authigenic materials such as silicate and phosphate minerals. Therefore, the whole rock compositions of carbonate rocks are not directly related with seawater composition. To avoid the influence of the involvement of the phosphate minerals, we performed the microscopic observation, elemental mapping of Si, Ca, Mg, Fe, and P contents with an electron probe microanalyzer (EPMA), and investigation of time profiles of signal intensities of Ca, Sr, Mn, P, La and Ba with the LA-ICP-MS. Especially, samples with low Mn/Sr ratios and primary textures such as oolites are suitable to estimate the primary phosphorus contents of the carbonates.The chemostratigraphy of the phosphorus contents of carbonates from the drill core and outcrop samples displays that the phosphorus contents decrease from ca. 400 ppm in the Ediacaran through ca. 200 ppm around the terminal Ediacaran and the beginning of the Cambrian to ca. 50 ppm in the early Cambrian. Previous works on ⁸⁷Sr/⁸⁶Sr chemostratigraphy from the Ediacaran to the Cambrian sections suggested relatively high continental influx in the middle Ediacaran, and around the Precambrian–Cambrian (PC/C) boundary. The high phosphorus content in the Ediacaran was possibly due to the high continental flux. On the other hand, previous works on chemostratigraphy of carbon isotope values of carbonate carbon from the Ediacaran to the Cambrian sections showed some large negative anomalies in the Ediacaran and around the Precambrian–Cambrian (PC/C) boundary, and suggested that the negative anomalies were caused by remineralization and respiration of dissolved organic matter. The degradation of the organic matter also accounts for the high phosphorus contents in the Ediacaran. The high phosphorus content of seawater favors enhancement of primary productivity and formation of phosphorites. The high phosphorus contents in the seawater possibly led to the emergence of the large, and motile organism through the enhancement of primary productivity and the consequent increase of oxygen content of the seawater.     

Ethnic enterprises and community development

Ethnic enterprises are growing rapidly in urban areas across the United States. Anecdotal evidence from around the country reports many success stories of how ethnic businesses transform communities; however, researchers have not provided a systematic review of the role of ethnic businesses in community developing. In practice, ethnic businesses have not been formally incorporated in local planning and development process. This article provides a systematic review of the multi-faceted ways ethnic businesses contribute to community building and neighborhood development. In addition to surveying the current literature, we also chose three communities for a focused review: Buford Highway in Atlanta, Monterey Park in Los Angeles, and Sunset Park in New York. A framework is developed to evaluate the economic, physical, social/cultural, and political effects that ethnic businesses exert on communities. We find that ethnic businesses can serve local economic interests and community-level cohesion and accrue economic, social, physical, and political benefits to their respective communities. These include serving the unmet market needs of certain neighborhoods and households, creating job opportunities and generating revenues, revitalizing and fueling the commercial development of abandoned communities, organizing and promoting social life and cultural diversity, as well as contributing their collective interest and voice in local communities. We argue that ethnic businesses should be better incorporated into urban policies in community economic development.     

寒武纪大爆发与动物树的成型

由“真动物”构成的动物界（不包括海绵）通常被划分为双胚层动物、原口动物和后口动物3个亚界。寒武纪大爆发经历了爆发的前奏—序幕—主幕3个阶段,其中后两个阶段处于早寒武世初期（依次以小壳化石的首次辐射和澄江动物群爆发为代表）,另一个则发生在“寒武前夜”（即前寒武纪末期）,以伊迪卡拉生物群为代表。这次独特的三幕式大爆发分步完成了动物形态演化谱系树（简写为TOA）的成型。已有化石证据显示,动物树的3大主体或3个亚界的起源及其早期辐射分别发生于寒武纪大爆发这3个主要阶段。澄江化石库中发现的早期后口动物亚界涵盖了该亚界中所有6大分支（棘皮类、半索类、头索类、尾索类、脊椎类和绝灭了的古虫类）的原始类群,澄江动物群时代标志着寒武纪大爆发的顶峰,完成了动物树框架的成型,从而宣告了寒武纪大爆发的基本终结。其学术重要性超越了中寒武世的布尔吉斯页岩,因为前者位于动物树形成的“源头”,而后者仅代表此后的“一段流程”。在动物演化历史上4个最具转折意义的重大创新事件（即多细胞动物起源、两侧对称动物起源、后口动物起源和脊椎动物起源）中,第一个发生在伊迪卡拉纪甚至更早的时期,其余3个则可通过梅树村化石群和澄江化石群观察到其完成的主体过程。已灭绝的古虫动物门,是初具鳃裂构造的原始分节动物,作为由原口动物向后口动物过渡的一个珍稀“缺环”,很可能代表着后口动物亚界的一个根。古囊类兼有两侧对称的古虫类和一些原始棘皮动物的镶嵌体征,最可能代表棘皮动物的一个根。在早寒武世动物演化谱系中,后口动物的＂顶端类群＂的代表是被誉为“第一鱼”的昆明鱼目,目前已知包括昆明鱼、海口鱼和钟健鱼,它们具对眼、脊索与串珠状脊椎软骨共存的原始脊椎,?