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.     

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.     

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.     

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.     

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.     

Biomats, biofilms, and bioglue as preservational agents for arthropod trackways

Due to divergent taphonomic selection, corresponding body and trace fossils are rarely found in the same rocks. In addition to this general rule, arthropod trackways are preferentially preserved in particular settings: (1) lithographic limestones, where toxic bottom waters account for the exceptional preservation of body fossils at the end of their “mortichnial” trackways; (2) estuarine and lacustrine biolaminites that yield blurred surface tracks as well as the sharper undertracks; and (3) Cambrian intertidal sands before the Precambrian/Cambrian substrate revolution had reached this environment. In all these ichnotopes, the original presence of protective microbial films can be inferred from sedimentary structures. By analogy, it is hypothesised that microbes (“bioglue”) may have been involved in the preservation of trackways in eolian dune sands. The absence of arthropod tracks in Ediacaran sands and silts means either that arthropods had not yet evolved or that they were as yet too tiny to pierce the tougher biomats of the time.     

Fuxianospira gyrata和Morania fragmenta(宏观藻类)在华北寒武系馒头组的发现

本文描述了山东省临朐县龙岗村寒武系苗岭统乌溜阶馒头组上页岩段的宏观藻类化石,计2属2种:环圈螺旋抚仙藻Fuxianospira gyrata Chen et Zhou, 1997和碎片玛拉利亚藻Morania fragmenta Walcott, 1919。这两种藻类在大小和形态上可与布尔吉斯页岩和澄江生物群中的宏观藻类相比较。本研究通过探讨藻体的长宽比,认为M.fragmenta的碎片状形态可能是藻体本身生长而成的形态,而不是其命名者所认为的碎裂而成的形态。这两个属种首次在馒头组的发现,拓展了其时空分布,为华北地区寒武纪宏观藻类研究提供了较有价值的资料。     

The morphology of Opabinia regalis and the reconstruction of the arthropod stem-group

Opabinia regalis Walcott is an enigmatic fossil from the Middle Cambrian Burgess Shale of uncertain affinities. Recent suggestions place it in a clade with Anomalocaris Whiteaves from the Burgess Shale and Kerygmachela Budd from the Greenlandic Sirius Passet Fauna; these taxa have been interpreted as 'lobopods'. Consideration of available Opabinia specimens demonstrates that reflective extensions from the axial region, previously thought to be either gut diverticula or musculature, can be accommodated in neither the trunk nor the lateral lobes that arise from it. They must therefore be external structures independent of the lateral lobes. On the basis of their sub-triangular appearance, size and taphonomy, they are considered here to represent lobopod limbs. Some evidence for the existence of terminal claws is also presented. The question of whether Kerygmachela, Opabinia and Anomalocaris constitute a monophyletic or paraphyletic grouping is considered. While they share several characters, most of these are plesiomorphies. Further, Opabinia and Anomalocaris share several arthropod-like characters not possessed by Kerygmachela. It is concluded that these three taxa probably form a paraphyletic grouping at the base of the arthropods. Retention of lobopod-like characters within the group provides important documentation of the lobopod-arthropod transition. A proper understanding of Opabinia and its close relatives, which may include the tardigrades, opens the way for a reconstruction of the arthropod stem-group. This in turn allows the construction of a speculative but satisfying scenario for the evolution of major arthropod features, including the origin of the biramous limb, tergites and arthropod segmentation. 'Arthropodization' may thus be seen not to be a single event but a series of adaptive innovations. OPABINIA, ANOMALOCARIS, KERYGMACHELA, Burgess Shale, problematica, Lobopodia, Arthropoda.     

Three-dimensional preservation of arthropod integument from the Middle Cambrian of Australia

Three-dimensional preservation of arthropod soft integument occurs in Middle Cambrian sediments of the Georgina Basin, western Queensland, Australia. The beds are referred to the Monastery Creek Phosphorite Formation, Gowers Formation, Inca Shale Formation and Devon-court Limestone Formation. The finds include arthropod type-A larvae previously described by Müller & Walossek and several complete appendages, possibly of early Palaeozoic 'ostracodes', as well as indeterminable cuticular remains. The Australian sediments were in part deposited under high water-energy conditions, whereas previously known occurrences of three-dimensional soft-integument preservation have been from environments of lower water energy. Such preservation may thus be more widespread in the Early Paleozoic than hitherto known. □ Phosphatization, arthropods, type-A larvae, appendages, Middle Cambrian, Geogina Basin, Australia, three-dimensional preservation.     

Cambrian bivalved arthropod reveals origin of arthrodization

Extant arthropods are diverse and ubiquitous, forming a major constituent of most modern ecosystems. Evidence from early Palaeozoic Konservat Lagerstätten indicates that this has been the case since the Cambrian. Despite this, the details of arthropod origins remain obscure, although most hypotheses regard the first arthropods as benthic predators or scavengers such as the fuxianhuiids or megacheirans (‘great-appendage’ arthropods). Here, we describe a new arthropod from the Tulip Beds locality of the Burgess Shale Formation (Cambrian, series 3, stage 5) that possesses a weakly sclerotized thorax with filamentous appendages, encased in a bivalved carapace, and a strongly sclerotized, elongate abdomen and telson. A cladistic analysis resolved this taxon as the basal-most member of a paraphyletic grade of nekto-benthic forms with bivalved carapaces. This grade occurs at the base of Arthropoda (panarthropods with arthropodized trunk limbs) and suggests that arthrodization (sclerotization and jointing of the exoskeleton) evolved to facilitate swimming. Predatory and fully benthic habits evolved later in the euarthropod stem-lineage and are plesiomorphically retained in pycnogonids (sea spiders) and euchelicerates (horseshoe crabs and arachnids).     

Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah

Garson, D.E., Gaines, R.R., Droser, M.L., Liddell, W.D. & Sappenfield, A. 2011: Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah. Lethaia, Vol. 45, pp. 164–177. Burgess Shale‐type faunas provide a unique glimpse into the diversification of metazoan life during the Cambrian. Although anoxia has long been thought to be a pre‐requisite for this particular type of soft‐bodied preservation, the palaeoenvironmental conditions that regulated extraordinary preservation have not been fully constrained. In particular, the necessity of bottom water anoxia, long considered a pre‐requisite, has been the subject of recent debate. In this study, we apply a micro‐stratigraphical, ichnological approach to determine bottom water oxygen conditions under, which Burgess Shale‐type biotas were preserved in the Middle Cambrian Spence Shale of Utah. Mudstones of the Spence Shale are characterized by fine scale (mm‐cm) alternation between laminated and bioturbated intervals, suggesting high‐frequency fluctuations in bottom water oxygenation. Whilst background oxygen levels were not high enough to support continuous infaunal activity, brief intervals of improved bottom water oxygen conditions punctuate the succession. A diverse skeletonized benthic fauna, including various polymerid trilobites, hyolithids, brachiopods and ctenocystoids suggests that complex dysoxic benthic community was established during times when bottom water oxygen conditions were permissive. Burgess Shale‐type preservation within the Spence Shale is largely confined to non‐bioturbated horizons, suggesting that benthic anoxia prevailed in intervals, where these fossils were preserved. However, some soft‐bodied fossils are found within weakly to moderately bioturbated intervals (Ichnofabric Index 2 and 3). This suggests that Burgess Shale‐type preservation is strongly favoured by bottom water anoxia, but may not require it in all cases. □Anoxia, Burgess Shale, Burgess Shale type‐preservation, Langston Formation, Spence Shale Member, Utah.     

贵州剑河中寒武世中期甲劳组水母状化石的发现

贵州剑河革东镇八郎村南甲劳组中部钙质白云岩中新近发现的具有粗强放射状辐管的水母状化石和其下凯里组中具细辐管及同心环的拟轮盘水母(Pararotadiscus)有明显区别,属于伊尔东钵科(Eldoniidae)。其层位晚于中寒武世早期凯里生物群中拟轮盘水母(Pararotadiscus)层位1个化石带,属中寒武世中期,是该类化石在中国的最高层位,相当于北美布尔吉斯页岩生物群中Eldonia化石层位。     

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 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.     

A new trace fossil from the Middle Cambrian of the Grand Canyon, Arizona, USA

An unusual trace fossil from the Middle Cambrian Bright Angel Shale Formation of the Grand Canyon, Arizona, consisting of two rows of biserially opposed circular or oval depressions, with alternating symmetry, is described as Bicavichnites martini ichnogen. et ichnosp. nov. While specimens of this trace may represent the surface expression of a complex treptichnid-like burrow system, it is more likely that they are the walking traces of a bilaterally symmetrical benthic animal. The large variation in external width within the trackways is inconsistent with an arthropod producer. The trackway morphology and presence of limb spur marks suggest that the trace maker may have been a lobopodian, a Cambrian relative of modern onychophorans.     

Exceptional fossil preservation and the cambrian explosion

Exceptionally preserved, non-biomineralizing fossils contributeimportantly to resolving details of the Cambrian explosion,but little to its overall patterns. Six distinct "types" ofexceptional preservation are identified for the terminal Proterozoic-Cambrianinterval, each of which is dependent on particular taphonomiccircumstances, typically restricted both in space and time.Taphonomic pathways yielding exceptional preservation were particularlyvariable through the Proterozoic-Cambrian transition, at leastin part a consequence of contemporaneous evolutionary innovations.Combined with the reasonably continuous record of "Doushantuo-typepreservation," and the fundamentally more robust records ofshelly fossils, phytoplankton cysts and trace fossils, thesetaphonomic perturbations contribute to the documentation ofmajor evolutionary and biogeochemical shifts through the terminalProterozoic and early Cambrian. Appreciation of the relationship between taphonomic pathwayand fossil expression serves as a useful tool for interpretingexceptionally preserved, often problematic, early Cambrian fossils.In shale facies, for example, flattened non-biomineralizingstructures typically represent the remains of degradation-resistantacellular and extracellular "tissues" such as chaetae and cuticles,whereas three-dimensional preservation represents labile cellulartissues with a propensity for attracting and precipitating earlydiagenetic minerals. Such distinction helps to identify theacuticular integument of hyolithids, the chaetae-like natureof Wiwaxia sclerites, the chaetognath-like integument of Amiskwia,the midgut glands of various Burgess Shale arthropods, and themisidentification of deposit-feeding arthropods in the Chengjiangbiota. By the same reasoning, putative lobopods in the SiriusPasset biota and putative deuterostomes in the Chengiang biotaare better interpreted as arthropods.     

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).     

Possible ctenophoran affinities of the Precambrian "sea-pen" Rangea

The Namibian Kuibis Quartzite fossils of Rangea are preserved three-dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand. The process of fossilization did not reproduce the original external morphology of the organism but rather the inner surface of collapsed organs, presumably a system of sacs connected by a medial canal. The body of Rangea had tetraradial symmetry, a body plan shared also by the White Sea Russian fossil Bomakellia and possibly some other Precambrian frond-like fossils. They all had a complex internal anatomy, smooth surface of the body, and radial membranes, making their alleged colonial nature unlikely. Despite a different style of preservation, the Middle Cambrian Burgess Shale frond-like Thaumaptilon shows several anatomical similarities to Rangea. The body plan of the Burgess Shale ctenophore Fasciculus, with its numerous, pinnately arranged comb organs, is in many respects transitional between Thaumaptilon and the Early Cambrian ctenophore Maotianoascus from the Chengjiang fauna of South China. It is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid of Thaumaptilon represent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs. These superficial structures were underlain by the complex serial organs, well represented in the fossils of Rangea. The Precambrian "sea-pens" were thus probably sedentary ancestors of the ctenophores.     

Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians

Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian ‘explosion’. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution—but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum—as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution.