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.     

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.     

Interpreting ‘shelly’ fossils preserved as organic films: the case of hyolithids

Most studies of Burgess Shale‐type preservation have focussed on soft‐bodied organisms, but ‘shelly’ fossils are also preserved as carbonaceous films. These films are usually interpreted as coherent organic layers – often external sheaths or periostracal layers – that were present in the original mineralized elements. The example of hyolithids shows that the organic films of skeletal parts do not represent original ‘layers’, but a composite resulting from the coalescence, into a single carbonaceous film, of all the preservable organic matter present in the skeletal element. The diagenetic processes that led to Burgess Shale‐type preservation, which involve the polymerization of organic matter and the loss of original internal structure and chemical integrity of the original tissues, are entirely compatible with – and could account for – the characteristics observed in the fossil films of hyolithid skeletal elements. These observations have general implications for the interpretation of other organisms preserved as carbonaceous films, such as the diverse and often problematic Cambrian sponges.     

Taphonomy of the middle Cambrian (Drumian) Ravens Throat River Lagerstätte,Rockslide Formation,Mackenzie Mountains,Northwest Territories,Canada

The Middle Cambrian (series 3, Drumian, Bolaspidella Biozone) Ravens Throat River Lagerstätte in the Rockslide Formation of the Mackenzie Mountains, northwestern Canada, contains a Burgess Shale‐type biota of similar age to the Wheeler and Marjum formations of Utah. The Rockslide Formation is a unit of deep‐water, mixed carbonate and siliciclastic facies deposited in a slope setting on the present‐day northwestern margin of Laurentia. At the fossil‐bearing locality, the unit is about 175 m thick and the lower part onlaps a fault scarp cutting lower Cambrian sandstones. It consists of a succession of shale, laminated to thin‐bedded lime mudstone, debris‐flow breccias, minor calcareous sandstone, greenish‐coloured calcareous mudstone and dolomitic siltstone, overlain by shallow‐water dolostones of the Broken Skull Formation, which indicates an overall progradational sequence. Two ~1‐m‐thick units of greenish calcareous mudstone in the upper part exhibit soft‐bodied preservation, yielding a biota dominated by bivalved arthropods and macrophytic algae, along with hyoliths and trilobites. It represents a low‐diversity in situ community. Most of the fossils occur in the lower unit, and only the more robust components are preserved. Branching burrows are present under the carapaces of some arthropods, and common millimetre‐sized disruptions of laminae are interpreted as bioturbation. The fossiliferous planar‐laminated calcareous mudstone consists of chlorite, illite, quartz silt, calcite and dolomite and is an anomalous facies in the succession. It was deposited via hemipelagic fallout of a mixture of platform‐derived and terrestrial mud. Geochemical analysis and trace‐element proxies indicate oxic bottom waters that only occasionally might have become dysoxic. Productivity in the water column was dominated by cyanobacteria. Fragments of microbial mats are common as carbonaceous seams. Complete decay of soft tissues was interrupted due to the specific sediment composition, providing support for the role of clay minerals, possibly chlorite, in the taphonomic process.     

Sediments of the Middle Cambrian Burgess Shale, Canada

The Phyllopod Bed of the Burgess Shale, in which Walcott found the famous soft bodied fossils, consists of thin graded beds of calcareous siltstone and mud-stone, which are probably turbidites. The Burgess Shale was deposited on a reef front submarine fan, and the preservation of the fossils is probably due to rapid burial.     

Palaeoredox geochemistry and bioturbation levels of the exceptionally preserved early Cambrian Indian Springs biota,Nevada, USA

The early Cambrian Indian Springs biota of western Nevada, USA, exhibits Burgess Shale‐type (BST) preservation of a diverse array of animal phyla, including the earliest definitive echinoderms. It therefore provides an important window on animal life during the Cambrian radiation. The objective of this study was to analyse the trace metal palaeoredox geochemistry and bioturbation levels of this BST deposit in order to characterize the palaeoenvironmental conditions in which these animals lived and their remains preserved. A total of 28 rock samples were collected from outcrops at three previously reported intervals of exceptional preservation at the Indian Springs locality, as well as from one interval not exhibiting such preservation. An additional 20 random samples were collected from talus for comparison. In the laboratory, the samples were analysed for trace metal palaeoredox indices (V/Cr and V/(V + Ni) ratios). Bioturbation levels were assessed through X‐radiography and petrographic thin sections using the ichnofabric index (ii) method. Additional samples from coeval strata of the Poleta Formation in the White‐Inyo Mountains, CA, that lack BST preservation were also analysed with the same methodology. Results indicate that oxic bottom water conditions dominated during deposition of these strata, despite consistently low bioturbation levels. This pattern holds for intervals with BST preservation and those without. Although ephemeral incursions of low‐oxygen waters may have taken place, there is no evidence for persistent oxygen restriction in these palaeoenvironments. The low levels of bioturbation indicate limited mixed layer development and a redox boundary near the sediment–water interface, likely allowing post‐burial BST preservation to occur even in this setting dominated by oxic bottom waters. Palaeoecological reconstructions and taphonomic hypotheses relating to the Indian Springs Lagerstätte must consider the palaeoredox conditions revealed in this study. With the dispensing of anoxic bottom waters as a requirement for BST preservation, other models proposing a role for clay minerals, the presence of hypersaline brines and the actions of Fe‐reducing bacteria as mechanisms for exceptional preservation warrant renewed consideration.     

A cryptic record of Burgess Shale‐type diversity from the early Cambrian of Baltica

Exceptionally preserved ‘Burgess Shale‐type’ fossil assemblages from the Cambrian of Laurentia, South China and Australia record a diverse array of non‐biomineralizing organisms. During this time, the palaeocontinent Baltica was geographically isolated from these regions, and is conspicuously lacking in terms of comparable accessible early Cambrian Lagerstätten. Here we report a diverse assemblage of small carbonaceous fossils (SCFs) from the early Cambrian (Stage 4) File Haidar Formation of southeast Sweden and surrounding areas of the Baltoscandian Basin, including exceptionally preserved remains of Burgess Shale‐type metazoans and other organisms. Recovered SCFs include taxonomically resolvable ecdysozoan elements (priapulid and palaeoscolecid worms), lophotrochozoan elements (annelid chaetae and wiwaxiid sclerites), as well as ‘protoconodonts’, denticulate feeding structures, and a background of filamentous and spheroidal microbes. The annelids, wiwaxiids and priapulids are the first recorded from the Cambrian of Baltica. The File Haidar SCF assemblage is broadly comparable to those recovered from Cambrian basins in Laurentia and South China, though differences at lower taxonomic levels point to possible environmental or palaeogeographical controls on taxon ranges. These data reveal a fundamentally expanded picture of early Cambrian diversity on Baltica, and provide key insights into high‐latitude Cambrian faunas and patterns of SCF preservation. We establish three new taxa based on large populations of distinctive SCFs: Baltiscalida njorda gen. et sp. nov. (a priapulid), Baltichaeta jormunganda gen. et sp. nov. (an annelid) and Baltinema rana gen. et sp. nov. (a filamentous problematicum).     

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.     

Why barren intervals? A taphonomic case study of the Scandinavian Alum Shale and its faunas

The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) accumulated under generally low oxygen concentrations. Syndepositional changes in the oxygen concentrations of the bottom water are reconstructed on the basis of the fossil fauna. Under relatively high oxygen concentrations, brachiopods and non-olenid polymerid trilobites inhabited the sea floor. Under lower oxygen concentrations the fauna was dominated by agnostids and at lowest oxygen levels by olenid trilobites. The enrichments of vanadium relative to nickel, as well as the enrichment of sulphur, match these faunal changes. A geochemical classification of the dysoxic environment is presented. The abundance of calcareous fossils decreases with increasing bottom water oxygen concentrations, indicating that the preservation of calcareous hard parts is most likely at the lowest oxygen concentrations. The poor preservation of calcareous fossils at relatively high oxygen concentrations is explained by the generation of corrosive pore waters during the reoxidation of sulphide compounds. Trilobitic and non-trilobitic intervals alternate up through the shale. Non-trilobitic intervals are either barren or contain non-calcareous fossils (phosphatic brachiopods, phosphatic 'ostracodes' and graptolites). The stratigraphical variation of trilobitic and non-trilobitic intervals is interpreted to reflect major changes in oxygen levels that might be linked to sea-level and climatic fluctuations.     

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.     

The Ediacaran Aspidella‐type impressions in the Jinxian successions of Liaoning Province,northeastern China

Macroscopic impression fossils from the Xingmincun Formation of the Jinxian Group, Liaoning Province of northeastern China, are identified as members of the Aspidella plexus of Ediacaran age. This is the first recognition of the taxon in the Liaoning Province, although such fossils have been previously recorded in the succession, but were referred to as new species and relegated to an earlier Neoproterozoic age. A revision of the taxonomic interpretation and relative age estimation of the previous record is provided, as well as an evaluation of abiotic vs. biotic processes that could produce similar structures to studied impressions. The mode of preservation of the fossils is considered from a biochemical point of view and along with the properties of organic matter in the integument of soft‐bodied metazoans. The selective preservation of the Ediacaran organisms, including metazoans, as impressions (moulds and casts) against the organically preserved contemporaneous cyanobacterial and algal microfossils, and an exceptionally small number of terminal Ediacaran metazoan fossils (Sabellidites, Conotubus and Shaanxilithes), demonstrates the non‐resistant characteristics and the very different biochemical constitution of the Ediacaran metazoans compared with those that evolved in the Cambrian and after. The refractory biomacromolecules in cell walls of photosynthesizing microbiota (bacterans, cutans, algaenan and sporopollenin groups) and in the chitinous body walls of Sabellidites contrast sharply with the labile biopolymers in Ediacaran metazoans known only from impressions. The newly emerging biosynthesis of resistant biopolymers in metazoans (chitin and collagen groups) initiated by the annelids at the end of Ediacaran and fully evolved in Cambrian metazoans, considered with the ability to biomineralize, made their body preservation possible. The Chengjiang and Burgess Shale metazoans show evidence of this new biochemistry in body walls and cuticles, and not only because of the specific taphonomic window that enhanced their preservation.     

The Sirius Passet Lagerstätte: silica death masking opens the window on the earliest matground community of the Cambrian explosion

The Sirius Passet Lagerstätte (SP), Peary Land, North Greenland, occurs in black slates deposited at or just below storm wave base. It represents the earliest Cambrian microbial mat community with exceptional preservation, predating the Burgess Shale by 10 million years. Trilobites from the SP are preserved as complete, three‐dimensional, concave hyporelief external moulds and convex epirelief casts. External moulds are shown to consist of a thin veneer of authigenic silica. The casts are formed from silicified cyanobacterial mat material. Silicification in both cases occurred shortly after death within benthic cyanobacterial mats. Pore waters were alkali, silica‐saturated, high in ferric iron but low in oxygen and sulphate. Excess silica was likely derived from remobilized biogenic silica. The remarkable siliceous death mask preservation opens a new window on the environment and location of the Cambrian Explosion. This window closed with the appearance of abundant mat grazers later as the Cambrian Explosion intensified.     

First record of the brachiopod Lingulella waptaensis with pedicle from the Middle Cambrian Burgess Shale

Pettersson Stolk, S., Holmer, L. E. and Caron, J ‐B. 2010. First record of the brachiopod Lingulella waptaensis with pedicle from the Middle Cambrian Burgess Shale. —Acta Zoologica (Stockholm) 91 : 150–162 The organophosphatic shells of linguloid brachiopods are a common component of normal Cambrian–Ordovician shelly assemblages. Preservation of linguloid soft‐part anatomy, however, is extremely rare, and restricted to a few species in Lower Cambrian Konservat Lagerstätten. Such remarkable occurrences provide unique insights into the biology and ecology of early linguloids that are not available from the study of shells alone. Based on its shells, Lingulella waptaensis Walcott, was originally described in 1924 from the Middle Cambrian Burgess Shale but despite the widespread occurrence of soft‐part preservation associated with fossils from the same levels, no preserved soft parts have been reported. Lingulella waptaensis is restudied herein based on 396 specimens collected by Royal Ontario Museum field parties from the Greater Phyllopod Bed (Walcott Quarry Shale Member, British Columbia). The new specimens, including three with exceptional preservation of the pedicle, were collected in situ in discrete obrution beds. Census counts show that L. waptaensis is rare but recurrent in the Greater Phyllopod Bed, suggesting that this species might have been generalist. The wrinkled pedicle protruded posteriorly between the valves, was composed of a central coelomic space, and was slender and flexible enough to be tightly folded, suggesting a thin chitinous cuticle and underlying muscular layers. The nearly circular shell and the long, slender and highly flexible pedicle suggest that L. waptaensis lived epifaunally, probably attached to the substrate. Vertical cross‐sections of the shells show that L. waptaensis possessed a virgose secondary layer, which has previously only been known from Devonian to Recent members of the Family Lingulidae.     

Graptolite (Hemichordata,Pterobranchia) preservation and identification in the Cambrian Series 3

Due to inadequate preservation, pterobranchs are often difficult to identify in the fossil record, and a better understanding of preservational modes and diagenetic and metamorphic effects is needed for their recognition. Pterobranch hemichordates are common in Cambrian Stage 5 and younger sedimentary rocks, but are frequently overlooked. Often, pterobranch hemichordate colonies have been considered to be algal remains or hydroids. Re‐examination of Cambrian Burgess Shale algae reveals that the genera Yuknessia and Dalyia can be recognized as putative early representatives of pterobranch hemichordates. Distinct fusellar construction of the individual zooidal tubes and branching of the creeping proximal part of the colonies are found in the morphologically similar rhabdopleurid pterobranch genus Sphenoecium. The erect tubes of Sphenoecium do not branch and can reach a length of several centimetres. The development of the fusellar construction in this taxon shows a highly irregular development of the suture patterns, but a fairly consistent height of the individual fuselli. The taxon is widely distributed in the Cambrian Series 3, but has regularly been identified as a hydroid or an alga. Sphenoecium wheelerensis from the Cambrian Wheeler Shale of Utah is described as new.     

AN ORDOVICIAN LOBOPODIAN FROM THE SOOM SHALE LAGERSTÄTTE, SOUTH AFRICA

Abstract:  The first lobopodian known from the Ordovician is described from the Soom Shale Lagerstätte, South Africa. The organism shows features homologous to Palaeozoic marine lobopodians described from the Middle Cambrian Burgess Shale, the Lower Cambrian Chengjiang biota, the Lower Cambrian Sirius Passet Lagerstätte and the Lower Cambrian of the Baltic. The discovery provides a link between marine Cambrian lobopodians and younger forms from the Silurian and Carboniferous. The new fossil preserves an annulated trunk, lobopods with clear annulations, and curved claws. It represents a rare record of a benthic organism from the Soom Shale, and demonstrates intermittent water oxygenation during the deposition of the unit.     

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.     

Explaining gregarious behaviour in Banffia constricta from the Middle Cambrian Burgess Shale,British Columbia

Banffia constricta is an enigmatic Burgess Shale animal originally described by Charles Walcott in 1911 as an annelid, and more recently as a stem‐group deuterostome. Interpreted, on the basis of anatomy, to have been bottom‐feeders, there are few other data from which to draw interpretations of Banffia's life habit. A slab of Burgess Shale with a dense aggregation of B. constricta may indicate a gregarious habit for the animal, as taphonomic and stratigraphical data indicate an in situ origin for the assemblage. Clustering of individuals, high density of the individuals and non‐random within‐cluster orientation support the hypothesis that detritus‐feeding B. constricta congregated to feed on a local, rich food source. Presumed opportunistic feeding aggregations have been documented in at least one other Burgess Shale taxon and have been described for other fossil benthic marine invertebrates. Extant benthic marine invertebrates such as holothurians and echinoids exhibit mass feeding behaviour and may serve as modern analogs for the behaviour represented by the B. constricta assemblage.     

贵州台江凯里动物群中的非钙质藻类化石

贵州台江凯里组的非钙质藻类化石在我国中寒武统尚属首次发现。国外主要见于北美。描述的非钙质藻类化石Ｍａｒｐｏｌｉａ ｓｐｉｓｓａ． Ｂｏｓｗｏｒｔｈｉａ ｓｉｍｕｌａｎｓ ,Ａｌｇａ ｇｅｎ． ｅｔ ｓｐ． ｉｎｄｅｔ, Ａ,Ａｌｇａ ｅｔｓｐ． ｉｎｄｅｔ, Ｂ等常见于北美布尔吉斯页岩动物群。当前中武寒武非钙质藻类化石的发现不仅填补了我国中寒武统非钙质藻类的空白,而且对于凯里动物群与布尔吉斯页斯     

A new shell-bearing organism from the Cambrian Spence Shale of Utah

A new shell-bearing organism with preserved soft tissue, Armilimax pauljamisoni n. gen. n. sp., is reported from the middle Cambrian (Miaolingian: Wuliuan) Miners Hollow locality of the Spence Shale of northern Utah. The described organism is known from a single articulated specimen and preserves a prominent shell, a slug-like body, as well as a U-shaped digestive tract. Its overall appearance is similar to halkieriids, but it does not preserve sclerites. The possible affinities of the new taxon and potential reasons for the presence of a U-shaped gut are discussed. Armilimax pauljamisoni is the first shell-bearing animal of its kind from the Great Basin and extends the diversity of body plans in the Spence Shale Fossil-Lagerstätte.