The nature and significance of the appendages of Opabinia from the Middle Cambrian Burgess Shale

Opabinia regalis has long been regarded as a curious animal, with its five eyes, its long flexible anterior process, and gill lamellae carried on the outside of overlapping lateral lobes. More recently, Opabinia has been reconstructed with lobopod limbs lying adaxial but separate from the lateral lobes. This version of Opabinia represented a lobopod–arthropod transition and prompted a hypothesis for the origin of the biramous limb that involved uniting the lobopod limb with a lateral lobe. New evidence of elemental maps is consistent with previous interpretations of the triangular structures in Opabinia as lateral extensions of the gut; there is no convincing evidence for the presence of lobopod limbs. Re-examination of critical specimens reveals that the gill lamellae are not on the outside of the lateral lobes. The limbs of Opabinia resemble the phyllopodous exopod of arthropods; the posterior margin is fringed with blades. Opabinia remains on the stem of euarthropods but not as a part of a paraphyletic Lobopodia. The Lobopodia is a clade of Cambrian armoured lobopods and onychophorans. A new hypothesis for the origin of the arthropod biramous limb from an exopod like that in Opabinia is presented, which involves an endite-bearing phyllopodous limb as an intermediate stage.     

New Middle Cambrian bivalved arthropods from the Burgess Shale (British Columbia,Canada)

The morphology of two new bivalved arthropods, Loricicaris spinocaudatus gen. et sp. nov. and Nereocaris briggsi sp. nov. from the middle Cambrian (Series 3, Stage 5) Burgess Shale Formation (Collins Quarry locality on Mount Stephen, Yoho National Park, British Columbia, Canada), is described. The material was originally assigned to the genus Branchiocaris, but exhibits distinctive character combinations meriting its assignment to other taxa. Loricicaris spinocaudatus possesses an elongate and spinose abdomen comparable to the contemporaneous Perspicaris and Canadaspis, as well as chelate second head appendages and subtriangular exopods, comparable to Branchiocaris. Nereocaris briggsi possesses a laterally compressed carapace, elongate and delicate appendages and a medial eye located between a pair of lateral eyes on a rhomboidal eye stalk. Although undoubtedly congeneric with Nereocaris exilis from a slightly younger horizon of the Burgess Shale Formation, N. briggsi differs in overall proportions and segment number, warranting assignment to a new species. The newly described taxa were coded into an extensive cladistic analysis of 755 characters, and 312 extinct and extant panarthropods, including a variety of Cambrian bivalved arthropods from both the Burgess Shale and the Chengjiang Lagerstätten. Cambrian bivalved arthropods consistently resolved as a paraphyletic assemblage at the base of Arthropoda. Important innovations in arthropod history such as the specialization of the deutocerebral head appendages and a shift from a nekton‐benthic deposit feeding habit to a benthic scavenging/predatory habit, the symplesiomorphic feeding condition of Euarthropoda (crown‐group arthropods), were found to have occurred among basal bivalved arthropods.     

Theoretical study on the body form and swimming pattern of Anomalocaris based on hydrodynamic simulation

Anomalocarid arthropod is the largest known predatory animal of middle Cambrian. Studies on Anomalocaris have been piled up in the past two decades since the first reasonable reconstruction had achieved in 1980s. Recent finding of legs beneath lobes on Parapeytoia Yunnanensis shows arthropod affinities, however, many researchers believe that it must be a powerful swimmer by the use of developed lobes. In this work, we investigate swimming behaviour of Anomalocaris in water by performing hydrodynamical calculation. As a result of simulation using moving particle method possible swimming motion of Anomalocaris is obtained. In the computer we can change the morphology from known bauplan of Anomalocaris found as fossil record. It makes us possible to discuss on the variants of Anomalocaris at the intermediate state of evolution process. Such new methodology using computer reveals how and from where Anomalocaris evolved.     

The bivalved arthropods Isoxys and Tuzoia with soft‐part preservation from the Lower Cambrian Emu Bay Shale Lagerstätte (Kangaroo Island,Australia)

Abstract: Abundant material from a new quarry excavated in the lower Cambrian Emu Bay Shale (Kangaroo Island, South Australia) and, particularly, the preservation of soft‐bodied features previously unknown from this Burgess Shale‐type locality, permit the revision of two bivalved arthropod taxa described in the late 1970s, Isoxys communis and Tuzoia australis. The collections have also produced fossils belonging to two new species: Isoxys glaessneri and Tuzoia sp. Among the soft parts preserved in these taxa are stalked eyes, digestive structures and cephalic and trunk appendages, rivalling in quality and quantity those described from better‐known Lagerstätten, notably the lower Cambrian Chengjiang fauna of China and the middle Cambrian Burgess Shale of Canada.     

A reevaluation of Wiwaxia and the polychaetes of the Burgess Shale

Wiwaxia corrugata and the indisputable polychaetes of the Middle Cambrian Burgess Shale, particularly Canadia spinosa, have figured prominently in recent hypotheses about the early evolution of polychaete annelids. Based on similarities between the sclerites of Wiwaxia and the notochaetae of Canadia with the broad notochaetae (paleae) of Recent chrysopetalid polychaetes, these two fossil taxa have been variously treated as closely related to the most highly derived stem forms of the polychaete (and annelid) crown group or as members of a specific, Recent subgroup within Polychaeta, the order Phyllodocida. Chrysopetalidae is a member of Phyllodocida, which is part of the major polychaete clade Aciculata; the latter two taxa are distinguished by four and six well defined autapomorphic characters, respectively. The best preserved or otherwise appropriate fossils of Wiwaxia corrugata, Canadia spinosa and the other polychaetes of the Burgess Shale have been studied in detail in order to determine whether they possess any characters that could support the homology of wiwaxiid sclerites, canadiid notochaetae and chrysopetalid paleae. Most of these fossil taxa have significant autapomorphies but the specific characters of the Aciculata and Phyllodocida are entirely absent. It is demonstrated that constraining cladograms in such a manner that wiwaxiid sclerites, canadiid notochaetae and chrysopetalid paleae are homologous leads to results that are markedly unparsimonious. Furthermore, Canadia and the other polychaetes of the Burgess Shale cannot be referred to any extant subgroup within the Polychaeta and cannot be used to polarize character evolution within the annelid crown group. Apart from its dubious sclerites, Wiwaxia has no characters that could indicate any close relationship with Polychaeta or Annelida.     

Skimming the surface with Burgess Shale arthropod locomotion

The first arthropod trackways are described from the Middle Cambrian Burgess Shale Formation of Canada. Trace fossils, including trackways, provide a rich source of biological and ecological information, including direct evidence of behaviour not commonly available from body fossils alone. The discovery of large arthropod trackways is unique for Burgess Shale-type deposits. Trackway dimensions and the requisite number of limbs are matched with the body plan of a tegopeltid arthropod. Tegopelte, one of the rarest Burgess Shale animals, is over twice the size of all other benthic arthropods known from this locality, and only its sister taxon, Saperion, from the Lower Cambrian Chengjiang biota of China, approaches a similar size. Biomechanical trackway analysis demonstrates that tegopeltids were capable of rapidly skimming across the seafloor and, in conjunction with the identification of gut diverticulae in Tegopelte, supports previous hypotheses on the locomotory capabilities and carnivorous mode of life of such arthropods. The trackways occur in the oldest part (Kicking Horse Shale Member) of the Burgess Shale Formation, which is also known for its scarce assemblage of soft-bodied organisms, and indicate at least intermittent oxygenated bottom waters and low sedimentation rates.     

A New Bivalved Arthropod from the Early Cambrian Sirius Passet Fauna, North Greenland

A new bivalved arthropod is described from the Lower Cambrian (?Upper Atdabanian) Buen Formation of North Greenland. Pauloterminus spinodorsalis gen. et sp. nov. possesses a bivalved carapace that covers the head, which has a single pair of antennae, and anteriormost thorax. No mouthparts are visible. The five‐segmented abdomen was limbless and terminated in a telson plus a pair of large, lobate uropods. A suite of at least six biramous thoracic limbs are present: the short endopods are made up of small, serial podomeres, while the exopods are lobate and may have functioned as gills as well as in swimming. Partially infilled guts are occasionally visible, suggesting that this animal may have been a sediment feeder. It is compared to other Cambrian bivalved arthropods, especially the waptiids Chuandianella ovata from the Lower Cambrian Chengjiang fauna (China) and Waptia fieldensis from the Middle Cambrian Burgess Shale (British Columbia). Of these three animals, the Greenland and Chinese taxa appear to be the most closely related. P. spinodorsalis possesses many typical arthropod features, but it also demonstrates more primitive characters that are more reminiscent of the lobopodians.     

Phylogenetic Significance of the Burgess Shale Crustacean Canadaspis

The crustaceans, like the other major living groups of arthropods, have a long evolutionary history. The earliest examples occur in the Cambrian, and fossils of this age are a critical source of evidence of relationships both within the Crustacea, and between the Crustacea and other major arthropod groups. Canadaspis perfecta, from the Middle Cambrian Burgess Shale, is important as one of the oldest well-documented crustaceans. The evidence for reconstructing its remarkable combination of primitive and derived characters is reviewed, and its possible phylogenetic significance re-assessed.     

Cambrian stem-group annelids and a metameric origin of the annelid head

The oldest fossil annelids come from the Early Cambrian Sirius Passet and Guanshan biotas and Middle Cambrian Burgess Shale. While these are among the best preserved polychaete fossils, their relationship to living taxa is contentious, having been interpreted either as members of extant clades or as a grade outside the crown group. New morphological observations from five Cambrian species include the oldest polychaete with head appendages, a new specimen of Pygocirrus from Sirius Passet, and an undescribed form from the Burgess Shale. We propose that the palps of Canadia are on an anterior segment bearing neuropodia and that the head of Phragmochaeta is formed of a segment bearing biramous parapodia and chaetae. The unusual anatomy of these taxa suggests that the head is not differentiated into a prostomium and peristomium, that palps are derived from a modified parapodium and that the annelid head was originally a parapodium-bearing segment. Canadia, Phragmochaeta and the Marble Canyon annelid share the presence of protective notochaetae, interpreted as a primitive character state subsequently lost in Pygocirrus and Burgessochaeta, in which the head is clearly differentiated from the trunk.     

The cuticle of the enigmatic arthropod Phytophilaspis and biomineralization in Cambrian arthropods

Lin, J.‐P., Ivantsov, A.Y. & Briggs, D.E.G. 2011: The cuticle of the enigmatic arthropod Phytophilaspis and biomineralization in Cambrian arthropods. Lethaia, Vol. 44, pp. 344–349. Many non‐trilobite arthropods occur in Cambrian Burgess Shale‐type (BST) biotas, but most of these are preserved in fine‐grained siliciclastics. Only one important occurrence of Cambrian non‐trilobite arthropods, the Sinsk biota (lower Sinsk Formation, Botomian) from the Siberian Platform, has been discovered in carbonates. The chemical compositions of samples of the enigmatic arthropod Phytophilaspis pergamena Ivantsov, 1999 and the co‐occurring trilobite Jakutus primigenius Ivantsov in Ponomarenko, 2005 from this deposit were analysed. The cuticle of P. pergamena is composed of mainly calcium phosphate and differs from the cuticle of J. primigenius, which contains only calcium carbonate. Phosphatized cuticles are rare among large Cambrian arthropods, except for aglaspidids and a few trilobites. Based on recent phylogenetic studies, phosphatization of arthropod cuticle is likely to have evolved several times. □arthropod cuticle, Burgess Shale‐type preservation, fossil‐diagenesis, phosphatization.     

Preservational folds simulating tergite junctions in tegopeltid and naraoiid arthropods

The exoskeleton in the Middle Cambrian Burgess Shale arthropod Tegopelte has previously been described as divided into tergites. Evidence from its sister taxon Saperion and from a Naraoia specimen from the Lower Cambrian Chengjiang fauna enables a reinterpretation of the suggested tergite boundaries in Tegopelte as preservational artefacts. They are considered here as folds that were formed during flattening of the undivided dorsal shield. As in the Naraoia specimen, the folds were initiated in the axial region between appendage pairs and then continue laterally. In Tegopelte and Saperion , segmentally arranged furrows in the axial region facilitated fold formation. Characters other than presence of thoracic tergites and pygidium must be used to assess the affinities of Tegopelte, Arthropoda, Tegopeltidae, tagmosis, segmentation, Chengjiang fauna, Burgess Shale.     

The macro‐ and microfossil record of the Cambrian priapulid Ottoia

The stem‐group priapulid Ottoia Walcott, 1911, is the most abundant worm in the mid‐Cambrian Burgess Shale, but has not been unambiguously demonstrated elsewhere. High‐resolution electron and optical microscopy of macroscopic Burgess Shale specimens reveals the detailed anatomy of its robust hooks, spines and pharyngeal teeth, establishing the presence of two species: Ottoia prolifica Walcott, 1911, and Ottoia tricuspida sp. nov. Direct comparison of these sclerotized elements with a suite of shale‐hosted mid‐to‐late Cambrian microfossils extends the range of ottoiid priapulids throughout the middle to upper Cambrian strata of the Western Canada Sedimentary Basin. Ottoiid priapulids represented an important component of Cambrian ecosystems: they occur in a range of lithologies and thrived in shallow water as well as in the deep‐water setting of the Burgess Shale. A wider survey of Burgess Shale macrofossils reveals specific characters that diagnose priapulid sclerites more generally, establishing the affinity of a wide range of Small Carbonaceous Fossils and demonstrating the prominent role of priapulids in Cambrian seas.     

Decline of the Burgess Shale fauna: ecologic or taphonomic restriction?

Aronson, R. B. 1992 07 15: Decline of the Burgess Shale fauna: ecologic or taphonomic restriction? An important alternative has not been tested in the debate over the origin, significance, and decline of Burgess Shale taxa: their observed stratigraphic distribution could be an artifact of increasing bioturbation. Based on information currently available, comparisons of the observed and expected stratigraphic distributions of Burgess Shale-type faunas falsify bioturbation as the exclusive cause. Ecological factors and/or taphonomic controls other than bioturbation were also responsible for the post-Cambrian decline of Burgess Shale-type faunas. Bioturbation, Burgess Shale fauna, soft-bodied animals, taphonomy.     

The Arthropod Alalcomenaeus cambricus Simonetta, from the Middle Cambrian Burgess Shale of British Columbia

More than 300 specimens of the previously rare arthropod Alalcomenaeus cambricus Simonetta have been collected from a new Burgess Shale locality in the Glossopleura Zone on Mount Stephen, British Columbia. This new material provides much more complete information on its morphology. The cephalon was covered by a shield. A pair of pedunculate eyes and three median eyes were followed by a large anterior appendage, the 'great appendage', bearing three long flagella. The two posterior head appendages, like those of the trunk, were biramous. They consisted of a segmented, inner branch, and a flap-like outer branch, fringed with long filaments. The trunk consisted of 11 somites, each protected by a tergite and bearing a pair of biramous limbs. The telson was paddle-like and fringed posteriorly with wide flat spines. Alalcomenaeus was probably a predator, moving mainly by swimming. It is now known to be one of the more abundant, widely distributed and longest ranging of Burgess Shale arthropod genera. Its affinities lie with the Arachnomorpha.     

Composition and preservation of the Chengjiang fauna –a Lower Cambrian soft-bodied biota

The Lower Cambrian Chengjiang fauna is reviewed and shown to be closely comparable with the younger Burgess Shale fauna. but with various differences in detail. A diverse group of more or less annulated lobopod animals including 'armoured lobopods' are regarded as representatives of the phylum Onychophora. 'Trilobitomorphs' include several new types. Probable protaspides of the trilobitomorph Naraoia are described. No molluses or deuterostomes have been identified. The preservational orientations of the various taxa are reviewed and compared with orientations of the Burgess Shale taxa. Orientation in the sediment is found to be closely correlated to the original shape of individuals. Several new genera and species are described: the segmented. worm-shaped Yunnanozoon lividum gen. et sp.n., the 'armoured lobopods' Onychodictyon ferox gen. et sp.n. and Cardiodictyon catenulum gen. et sp.n. and the arthropods Saperion glumaceum gen. et sp.n., Sinoburius Iunaris gen. et sp.n., and Xandarella spectaculum gen. et sp.n.     

Cephalic and appendage morphology of the Cambrian arthropod Sidneyia inexpectans

Sidneyia inexpectans Walcott, 1911 from the Cambrian Series 3 Burgess Shale of British Columbia is largely accepted as a representative of the artiopodans, an assemblage of Paleozoic arthropod taxa, including trilobites and their immediate relatives. Its appendage morphology was never fully understood, but the exopod seemed to differ from that of other artiopodans, except for the shared presence of lamellae. The head was considered to comprise only the ocular and antennular segments, these being covered entirely on the ventral side by a large doublure. This short head was often taken as an evidence for variability of head segment counts in Cambrian arthropods, and to falsify the hypothesis of a head with three postantennular segments in the euarthropod ground pattern. Restudy of a substantial amount of material of S. inexpectans shows that previous interpretations of a short head were based on taphonomically deformed specimens, where the head was either partly folded, or entirely flipped under the thorax, resulting in the dorsal shield being mistaken for an extensive doublure. Rather than an extensive doublure, there is a broad hypostome, and the head comprises ocular, antennular, and at least two postantennular appendage bearing segments. The appendage morphology is shown to be consistent with artiopodan affinities. The exopod is of the bilobate flap-like type with lamellae inserting on the proximal portion, earlier proposed as a potential autapomorphy of Artiopoda. Reinforcement of artiopodan affinities for S. inexpectans and reinterpretation of its head reconciles this species with current understanding of arthropod phylogeny and head segmentation.     

英文贵州中寒武世凯里生物群中宏观藻类化石新材料(英文)

贵州省台江县中寒武世凯里生物群含有丰富的非钙质藻类和具有软躯体后生动物化石 ,它为布尔吉斯页岩型生物群在世界广泛分布提供了更有力的证据。在生物群的宏观藻类中描述了 5个属 5个种 ,包括 2个新属。它们是MarpoliaspissaWalcott、AcinocricusstichusConwayMorrisandRobison、UdotealgaerectaYang、EosargassumsawataYang和RhizophytonzhaoyuanlongiiYang ,并且将凯里生物群中的宏观藻类化石组合与加拿大布尔吉斯页岩生物群中的宏观藻类进行了对比 ,发现两个生物群不仅具有相似的动物化石组成 ,而且宏观藻类化石组成也很相似。     

The accessory lateral eye of a diplopod, Cylindroiulus truncorum (Silvestri, 1896) (Diplopoda: Julidae)

Using electron microscopy we describe an accessory lateral eye for Cylindroiulus, a diplopod. The accessory eye is situated at the cell body rind of the optic lobes, deep inside the head, and is composed of six R-cells; a dioptric apparatus is absent. Comparison reveals that many arthropods possess accessory lateral eyes in addition to the compound eyes or lateral ocelli. Their homology and distribution among the arthropod main lineages is discussed along with characters that may be useful for reconstructing phylogeny.