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。     

节肢动物吐卓虫咬痕化石在云南昆明附近寒武纪早期关山生物群的发现及意义*

本文报道了一块来自云南省昆明市附近寒武纪第二世第四期关山生物群具咬痕的双瓣壳节肢动物吐卓虫 (Tuzoia)化石, 系吐卓虫咬痕化石在全球范围的首次发现。该发现证实作为主动捕食者的吐卓虫很可能被大型捕食者(如奇虾类或莱德利基虫类三叶虫等)捕食, 说明寒武纪早期的海洋生物群落已经具有高度复杂化的食物链, 为进一步了解吐卓虫的生态位及深入探讨寒武纪大爆发时期海洋生态系统食物网结构提供了新的信息。     

节肢动物吐卓虫咬痕化石在云南昆明附近寒武纪早期关山生物群的发现及意义*

本文报道了一块来自云南省昆明市附近寒武纪第二世第四期关山生物群具咬痕的双瓣壳节肢动物吐卓虫 (Tuzoia)化石, 系吐卓虫咬痕化石在全球范围的首次发现。该发现证实作为主动捕食者的吐卓虫很可能被大型捕食者(如奇虾类或莱德利基虫类三叶虫等)捕食, 说明寒武纪早期的海洋生物群落已经具有高度复杂化的食物链, 为进一步了解吐卓虫的生态位及深入探讨寒武纪大爆发时期海洋生态系统食物网结构提供了新的信息。     

Trilobites within nautiloid cephalopods

'Sheltered preservation' of the remains of trilobites within the shells of nautiloid cephalopods is not especially uncommon. In most cases, of course, both the trilobites and the nautiloids were dead, and the association, merely due to post-mortem happenstance. However, on the basis of state of preservation and occurrence, a number of live individuals of the trilobite genera Acidaspis, Flexicalymene, and Isotelus from the Ordovician of the United States and of Alcymene and Encrinuraspis from the Silurian of Wales and the Czech Republic seem to have entered conchs of dead cephalopods, presumably for refuge.     

The Origin and Initial Rise of Pelagic Cephalopods in the Ordovician

Background

During the Ordovician the global diversity increased dramatically at family, genus and species levels. Partially the diversification is explained by an increased nutrient, and phytoplankton availability in the open water. Cephalopods are among the top predators of todays open oceans. Their Ordovician occurrences, diversity evolution and abundance pattern potentially provides information on the evolution of the pelagic food chain.

Methodology/Principal Findings

We reconstructed the cephalopod departure from originally exclusively neritic habitats into the pelagic zone by the compilation of occurrence data in offshore paleoenvironments from the Paleobiology Database, and from own data, by evidence of the functional morphology, and the taphonomy of selected cephalopod faunas. The occurrence data show, that cephalopod associations in offshore depositional settings and black shales are characterized by a specific composition, often dominated by orthocerids and lituitids. The siphuncle and conch form of these cephalopods indicate a dominant lifestyle as pelagic, vertical migrants. The frequency distribution of conch sizes and the pattern of epibionts indicate an autochthonous origin of the majority of orthocerid and lituitid shells. The consistent concentration of these cephalopods in deep subtidal sediments, starting from the middle Tremadocian indicates the occupation of the pelagic zone early in the Early Ordovician and a subsequent diversification which peaked during the Darriwilian.

Conclusions/Significance

The exploitation of the pelagic realm started synchronously in several independent invertebrate clades during the latest Cambrian to Middle Ordovician. The initial rise and diversification of pelagic cephalopods during the Early and Middle Ordovician indicates the establishment of a pelagic food chain sustainable enough for the development of a diverse fauna of large predators. The earliest pelagic cephalopods were slowly swimming vertical migrants. The appearance and early diversification of pelagic cephalopods is interpreted as a consequence of the increased food availability in the open water since the latest Cambrian.     

Cambrian biostratigraphy of the Bowers back-arc basin,Northern Victoria Land,Antarctica — A review

The Bowers Mountains in Northern Victoria Land contain the richest Cambrian Series 3 (Miaolingian, middle Cambrian) and Cambrian Series 4 (Furongian, late Cambrian) fossiliferous successions in Antarctica. Almost all the fossils are found within the Bowers Supergroup, which outcrops within the Bowers Terrane, a fault-bounded northwest-southeast oriented strip in Northern Victoria Land. The fossils provide the main age control on the history and evolution of the Bowers volcanic arc and back-arc basin. The great bulk of the fossils occur within the Spurs Formation. The fossil assemblages are dominated by agnostoids and polymerid trilobites with most ranging in age from Drumian to Paibian, although one fauna is of Jiangshanian age. Over 40 agnostoid taxa and over 100 polymerid trilobite taxa have been recorded from the rocks of the Bowers Supergroup. The youngest fauna occurs within the adjacent Robertson Bay Terrane, where a limited fauna of polymerid trilobites and conodonts from within a limestone olistolith have a very late Cambrian or early Ordovician age. Faunal affinities are mainly with Australia, New Zealand, North and South China and the Himalaya with lesser ties to Iran, Kazakhstan, Siberia and Laurentia.     

A tiny eye indicating a planktonic trilobite

Abstract: Cambrian trilobites mainly lived on the sea floor, and up till now few, if any, unequivocally planktonic trilobites have been reported from earlier than the Ordovician. The late Cambrian (Furongian) to late Ordovician olenids are a distinctive group of benthic (sea‐floor dwelling) or nekto‐benthic trilobites. Here we show, however, that one recently described, miniaturized and very spiny olenid species, Ctenopyge ceciliae must have been planktonic (passively drifting or feebly swimming in the upper waters of the sea). This interpretation is based not only upon body form but also on the analysis of its visual system and may be one of the earliest records of the planktonic realm being invaded by trilobites.     

The life habits of the Ordovician illaenine trilobite Bumastoides

The Ordovician illaenine Bumastoides exhibits a distinctive effaced and strongly convex morphology. Orientation of the visual field, the extreme convexity of the cephalon and the nature of the thoracic articulation support an interpretation of Bumastoides as an infaunal trilobite that was poorly suited to epifaunal crawling. The genus may have been sedentary; spending most of its post-larval life cycle within a burrow. Suspension feeding would be a viable existence for a sedentary trilobite such as Bumastoides. Maintenance of a burrow is essential for respiration and would require a firm, cohesive substrate. The infaunal niche had become occupied by trilobites by at least the Late Cambrian and continued to be exploited through the Ordovician, Silurian and. possibly, into the Devonian. Convergence has led to the appearance of the effaced, strongly convex morphotype in a number of unrelated families, including the Illaenidae, Asaphidac, Aulacopleuridae, Plethopeltidae and Scutelluidae. A high numerical abundance of illaenid trilobites, such as Illaenus and Bumastoides , is characteristic of the illaenid–chcirurid association, which persisted from the early Ordovician until at least the Late Silurian. This association has been recorded from shelf-edge and on-shelf carbonate buildups and shallow subtidal level bottom environments. It appears to be confined to firm substrates.     

Shell microstructure of the early bivalve Pojetaia and the independent origin of nacre within the mollusca

Abstract: Pojetaia and Fordilla are the oldest bivalve molluscs, occurring in roughly co‐eval rocks from the Tommotian, and are the only undisputed, well‐known bivalves from the Cambrian. New specimens reveal that Pojetaia had a laminar inner shell microstructure reminiscent of the foliated aragonite of modern monoplacophorans, and the same is true for Fordilla. A similar shell microstructure is seen in Anabarella and Watsonella, providing support for the hypothesis that they are the ancestors of bivalves. Foliated aragonite shares many similarities with nacre, and it may have been the precursor to nacre in bivalves. No cases of undisputed nacre occur in the Cambrian, in spite of much shell microstructure data from molluscs of this time period. Thus, although considered by many to be homologous among molluscs, we conclude that nacre convergently evolved in monoplacophorans, gastropods, bivalves, and cephalopods. This independent origin of nacre appears to have taken place during, or just prior to, the Great Ordovician Biodiversification Event and represents a significant step in the arms race between predators and molluscan prey.     

Restudy of some Ordovician–Silurian boundary graptolites from Anticosti Island, Canada, and their biostratigraphic significance

The Ellis Bay Formation on Anticosti Island has long been recognized for the biostratigraphic importance of its latest Ordovician conodont, palynomorph, and shelly fossil assemblages. However, a sparse record of graptolites has made it difficult to correlate these assemblages with the graptolite biozonation. Restudy of some previously described and examination of newly collected normalograptid specimens from the Ellis Bay and lower Becscie formations, however, shows that biostratigraphically important taxa are present and these species provide important constraints on the age of the strata. Normalograptus parvulus and N. minor have been identified in the upper half of the Ellis Bay Formation, suggesting that these strata are late Hirnantian in age ( N. persculptus Biozone). Normalograptus imperfectus and Normalograptus sp. aff. N. acceptus occur in the basal beds of the Becscie Formation, indicating that these strata are earliest Silurian. These graptolite data support the hypothesis that the positive carbon isotope excursion seen in the uppermost strata of the Ellis Bay Formation is isochronous with that seen in the Hirnantian strata at Dob's Linn, Scotland, and does not span much of the lower to mid-Hirnantian, as is the case in Arctic Canada and Nevada, USA.     Anticosti Island , Hirnantian, graptolites, Ordovician, Silurian.     

Ordovizium und Silur. Überschwemmungen,eine Eiszeit und die Eroberung des Festlandes

Ordovician and Silurian sediments are predominantly black shales formed from anoxic pelagic environments. Adjacent shallow marine areas are represented by reefs and well‐sorted sands deposited worldwide on continental shelves. Pelagic realms hosted a great variety of graptolite colonies which due to their rapid evolution are excellent index fossils besides a multitude of new species of trilobites and brachiopods. Reef builders were mainly bryozoans and tabulate corals. During the Ordovician, the earliest spores mark the beginning conquest of land by plants. A mass extinction at the end of the Ordovician was probably caused by a worldwide climatic change which is also evident from traces of a contemporaneous glaciation.     

Boring Late Cambrian organisms

Specimens of inarticulate brachiopods (family Acrotrctidae) with boreholes were found in Upper Cambrian carbonates in the southern Great Basin of the United States. Some morphologic features and preferred orientation of the borings are similar to those made by predators and previously reported in the fossil and Holocene record. Such predatory activity on brachiopods is previously unknown in Cambrian rocks. Taxa associated with these specimens are not known to have been predators and identity of the predatory organism is unknown. Cambrian brachiopods, predation, paleoecology.     

Structures coaptatives et enroulement chez quelques Trilobites ordoviciens et siluriens

Clarkson, E. N. K. & Henry, J. L.: Structures coaptatives et enroulement chez quelques Trilobites ordoviciens et siluriens. [Coaptative structures and enrollment in some Ordovician and Silurian trilobites.]
Certain trilobites possessed highly adapted structures on the cephalon and pygidium, and sometimes also the thorar, which ensured very close interlocking of opposing surfaces during enrollment. Different kinds of structures are described in detail in selected Ordovician and Silurian genera. There is a simple 'press-stud' mechanism axially situated on the opposing cephalic and pygidial doublures of Kloucekia micheli , whereas in various species of Crozonaspis and in Kloucekia dujardini a projecting cephalic beak fits into an excavation under the caudal spine. The cephalic beak and corresponding pygidial excavation seemingly evolve towards a more pronounced form in successive species throughout time. Colpocoryphe rouaulti , by contrast, has a pygidial protuberance interlocking with a cephalic excavation. Complete specimens of Encrinurus tuberculatus and E. variolaris have very complex contact surfaces along opposing doublures, with various kinds of interlocking structures.     

Traces of predation in the Cambrian

Series two marks a revolution in Cambrian predation when new predators and new predation methods appeared, which led to general increase in predation intensities and in the diversity of prey groups. The number of bored taxa and taxa with the predation scars is similar in the Cambrian. Most of the borings are associated with brachiopods and most of the scars with trilobites. Brachiopods, arthropods, molluscs, cnidarians and echinoderms were the most common prey in the Cambrian. The Cambrian record of predation is dominated by damage inflicted on brachiopods and trilobites. The fossils with predation signs are known from a majority of paleocontinents and all the Cambrian series.     

Predation in the Ordovician and Silurian of Baltica

Signs of predation appear in the Middle Ordovician of Baltica. Shell repair dominates over the predatory borings in the Ordovician and Silurian. Predators attacked molluscs, brachiopods and tentaculitoids in the Ordovician and molluscs, tentaculitoids, brachiopods and ostracods in the Silurian. There is an increase in the number of prey species in the Late Ordovician, which could be related to the Great Ordovician Biodiversification Event. Molluscs are the favourite prey taxon in the Ordovician, but in the Silurian, molluscs became less dominant as the prey. This is probably not an artefact of preservation as Ordovician and Silurian molluscs are equally well preserved.     

Facies distribution patterns of some marine benthic faunas in early paleozoic platform environments

Worldwide Late Cambrian—Silurian lithofacies patterns indicate that the platforms of that time were sites of accumulation of two essentially different rocks suites: the platform carbonate rocks and the platform terrigenous rocks. Most of the platform rocks accumulated as sediments in shallow marine environments similar to those of the present but far more widely spread.Present-day marine benthic faunas are distributed in depth zones which are primarily controlled by temperature. Faunas tend to occur in substrate-related discrete clusters (communities) within each life zone; similar substrates in different depth zones commonly have different faunal associations. Individual phyletic stocks may encounter environmental optimum or near-optimum conditions in certain areas, that commonly are revealed by an abundance of species and individuals within species in each stock. Environmental optimum conditions depend upon availability of food that may be utilized, modes of feeding of the animals present, water motion, and substrate, among other factors. Organisms in past seas were distributed in patterns similar to those of the present.Carbonate platforms were particularly widespread during the latest Cambrian—Early Ordovician. Intertidal environments spread widely across those platforms during that time and characteristic faunal associations developed in them. Saukiid and related tribolites dominated latest Cambrian carbonate platform intertidal faunas. The Early Ordovician carbonate platform intertidal was dominated by archeogastropod-nautiloid cephalopod faunas. These animals were joined by tabulate corals and certain brachiopods during the latter part of the Ordovician and Silurian as prominent faunal elements in the carbonate platform intertidal—shallow subtidal. Cruziana and related trace fossils, bivalves, and certain tribolites (notably homalonotids and dalmanitids) dominated most terrigenous platform intertidal—shallow subtidal faunas of the Ordovician and Silurian.Articulate brachiopods (primarily orthoids, strophomenoids, and rhynchonelloids) appear to have been relatively prominent during the Early Ordovician in shallow subtidal environments on both carbonate and terrigenous platforms and to have spread down the bathymetric gradient into increasingly deeper subtidal areas of both platforms during the latter part of the Ordovician. Tribolites dominated faunas in relatively moderate to deep subtidal environments on both platforms during the early part of the Ordovician. They were gradually replaced by brachiopods in first the shallower, and later the deeper subtidal as dominant members of the faunas. Brachiopods (primarily pentameroids and spiriferoids) dominated nearly all Silurian warm-water subtidal environments from the shallow subtidal to the edges of the platforms.Platform uplifts in the Middle Ordovician and glacio-eustatic sea-level fluctuations in the Late Ordovician caused environmental changes across the platforms that were accompanied by marked replacements among marine benthic faunas in all environments. The distribution of Ordovician carbonate platforms and glacial deposits suggests that an Ordovician polar region may have been close to present-day equatorial Africa and that Ordovician warm temperate-tropical regions lay close to the present-day North Pole.     

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。     

陕西梁山地区宝塔组介形类

本文报道了陕西省南郑县梁山地区中奥陶统宝塔组介形类8属10种,其中包括3新属8新种。这些介形类化石的发现,为该时代地层的划分、对比增添了新的古生物依据。     

The Phylogeny and Systematics of Blind Cambrian Ptychoparioid Trilobites

The paraphyletic trilobite suborder Ptychopariina includes a large proportion of Cambrian trilobite diversity and is probably ancestral to most groups of post-Cambrian trilobites. Resolution of the phylogenetic relationships within the group is therefore crucial to a better understanding of the initial radiation of trilobites. The recognition of approaches that can successfully resolve the relationships of ptychoparioid taxa is an important first step towards this aim. Cladistic analysis was used to determine relationships within the Cambrian ptychoparioid trilobite family Conocoryphidae, and to test claims that the family is polyphyletic. Ninety-seven characters were coded for 40 conocoryphid species and nine non-conocoryphids. The results indicate that the family consists of four distantly related clades. Three are recognized here as distinct families, including an extensively revised Conocoryphidae, and the families Holocephalidae and Atopidae. The fourth clade is referred to the subfamily Acontheinae (Corynexochida) as the new Tribe Hartshillini. Analysis of the disparity of these four clades shows that they are significantly less morphologically variable than the original polyphyletic taxon, demonstrating the possible effects of taxonomic error on macroevolutionary studies of morphological disparity.     

Gut evolution in early Cambrian trilobites and the origin of predation on infaunal macroinvertebrates: evidence from muscle scars in Mesolenellus

Trilobites are particularly common Cambrian fossils, but their trophic impact on the rapidly evolving marine ecosystems of that time is difficult to assess, due to uncertainties on how diverse their feeding habits truly were. Gut anatomy might help to constrain inferences on trilobite feeding ecology, but preservation of digestive organs is exceedingly rare. Muscle scars on the glabella, known as ‘frontal auxiliary impressions’ (FAIs), have been interpreted as evidence of the evolution of a pouch‐like organ with powerful extrinsic muscles (i.e. a crop) in some trilobites. Here we describe FAIs in Mesolenellus hyperboreus from Cambrian Stage 4 strata of North Greenland, which represents the oldest example of such structures and their first report in the Suborder Olenellina. Mesolenellus FAIs suggest that the crop in trilobites was clearly differentiated from the rest of the digestive tract, and essentially located under a hypertrophied glabellar frontal lobe. Reviews of the digestive anatomy of trilobite sister‐taxa and the glabellar morphology of the oldest‐known trilobites suggest that the gut of the trilobite ancestor was an essentially simple tract (i.e. no well‐differentiated crop) flanked laterally by numerous midgut glands. A crop first evolved in the Cambrian in groups like olenelloids and (later) paradoxidoids. Using ichnological evidence, we hypothesize that the emergence of olenelloids yields evidence for the evolution of predatory inclinations in a group of arthropods originally dominated by surface‐deposit‐feeders. By allowing the exploitation of a rapidly developing food source, infaunal animals, the diversification of feeding strategies in trilobites might partially explain their unparalleled evolutionary success.