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.     

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.     

Palaeoceanographic redox environments for the lower Cambrian Hetang Formation in South China: Evidence from pyrite framboids,redox sensitive trace elements,and sponge biota occurrence

The lower Cambrian Hetang Formation, a black shale sequence, contains a stone coal (a flammable, organic-rich mudstone) unit. Abundant pyrite framboids occur in this unit, with the average mean sizes falling in a narrow range from 4.6 to 5.4 μm and the maximum diameters being around 10 μm. The size distribution pattern of the pyrite framboids indicates a euxinic depositional environment. The redox-sensitive trace metals of the stone coal samples reveal a large enrichment of Mo (10–180 times),V (4–40 times), U (10–60 times) and Ni (2–20 times) compared to the average upper continental crust value, consistent with an anoxic environment for their deposition. The redox-sensitive element ratios (Th/U, V/(V + Ni), V/Cr) indicate that the depositional environment for the lower part of the stone coal unit was the most anoxic and euxinic. In contrast, a sponge biota including eleven species of demosponges and hexactinellids and two undetermined forms indicate an oxic or dysoxic environment. To reconcile these two facts, we propose that although an anoxic/euxinic environment predominated during the deposition of the lower Cambrian Hetang Formation black shales, occasional currents may also have brought free oxygen to the bottom water column to allow the growth of the sponges on the sea floor.     

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.     

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.     

Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte,lower Cambrian of North Greenland

Stein, M., Peel, J.S., Siveter, D.J. & Williams, M. 2009: Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. Lethaia, Vol. 43, pp. 258–265. Isoxys volucris is the most commonly occurring species in the lower Cambrian Sirius Passet Lagerstätte of North Greenland. Newly identified material allows a first, limited, account of the ventral morphology of this species, hitherto known only by the morphology of its shield. The antennula is large and robust, composed of about seven articles armed with spines, and was probably not sensorial. The postantennular limbs are serially similar, biramous with a large paddle‐shaped exopod fringed with setae. It is possible that the animal possessed a furca. The inner lamella, lining the ventral surface of the shield is recognised in Isoxys for the first time. Comparisons with other congeneric species of which aspects of the ventral morphology are known, show similarities with Isoxys auritus from China, reconsidered here, but indicate differences in antennular morphology with other species as currently understood. □Cambrian, Greenland, Isoxys, soft anatomy, Sirius Passet, palaeoecology.     

A crown‐group demosponge from the early Cambrian Sirius Passet Biota,North Greenland

Calibration of the divergence times of sponge lineages and understanding of their phylogenetic history are hampered by the difficulty in recognizing crown versus stem groups in the fossil record. A new specimen from the lower Cambrian (Series 2, Stage 3; approximately 515 Ma) Sirius Passet Biota of North Greenland has yielded a diagnostic spicule assemblage of the extant demosponge lineages Haploscleromorpha and/or Heteroscleromorpha. The specimen has disarticulated approximately in situ, but represents an individual sponge that possessed monaxon spicules combined with a range of slightly smaller sigma, toxa and unique spiral morphologies. The combination of spicule forms, together with their relatively large size, suggests that the sponge represents the stem lineage of Haploscleromorpha + Heteroscleromorpha. This is the first crown‐group demosponge described from the early Cambrian and provides the most reliable calibration point currently available for phylogenetic studies.     

Global marine redox changes drove the rise and fall of the Ediacara biota

The role of O₂ in the evolution of early animals, as represented by some members of the Ediacara biota, has been heavily debated because current geochemical evidence paints a conflicting picture regarding global marine O₂ levels during key intervals of the rise and fall of the Ediacara biota. Fossil evidence indicates that the diversification the Ediacara biota occurred during or shortly after the Ediacaran Shuram negative C‐isotope Excursion (SE), which is often interpreted to reflect ocean oxygenation. However, there is conflicting evidence regarding ocean oxygen levels during the SE and the middle Ediacaran Period. To help resolve this debate, we examined U isotope variations (δ²³⁸U) in three carbonate sections from South China, Siberia, and USA that record the SE. The δ²³⁸U data from all three sections are in excellent agreement and reveal the largest positive shift in δ²³⁸U ever reported in the geologic record (from ~ ?0.74‰ to ~ ?0.26‰). Quantitative modeling of these data suggests that the global ocean switched from a largely anoxic state (26%–100% of the seafloor overlain by anoxic waters) to near‐modern levels of ocean oxygenation during the SE. This episode of ocean oxygenation is broadly coincident with the rise of the Ediacara biota. Following this initial radiation, the Ediacara biota persisted until the terminal Ediacaran period, when recently published U isotope data indicate a return to more widespread ocean anoxia. Taken together, it appears that global marine redox changes drove the rise and fall of the Ediacara biota.     

Vetulicolians from the Lower Cambrian Sirius Passet Lagerstätte,North Greenland,and the polarity of morphological characters in basal deuterostomes

Abstract: Vetulicolians are problematic Cambrian fossils with a debated phylogenetic history. Here, we describe two vetulicolian specimens from the Lower Cambrian Sirius Passet locality in North Greenland. One of the specimens is assigned to Ooedigera peeli gen. et sp. nov, whereas the other is retained under open nomenclature. The mode of tail flexibility has been debated in the literature, and we argue here that the tail normally flexed laterally to generate power strokes rather than dorsoventrally. The phylogenetic relationships of vetulicolians are discussed in the light of current knowledge of deuterostome phylogeny and morphology, and it is concluded that the best hypothesis on currently available evidence is that vetulicolians are a clade or paraphyletic assemblage of stem‐Deuterostomata. The presence of a voluminous, sediment‐filled anterior chamber suggests that the atrium may be a synapomorphy of deuterostomes.     

Onychophoran‐like myoanatomy of the Cambrian gilled lobopodian Pambdelurion whittingtoni

Arthropods are characterized by a rigid, articulating, exoskeleton operated by a lever‐like system of segmentally arranged, antagonistic muscles. This skeletomuscular system evolved from an unsegmented body wall musculature acting on a hydrostatic skeleton, similar to that of the arthropods’ close relatives, the soft‐bodied onychophorans. Unfortunately, fossil evidence documenting this transition is scarce. Exceptionally‐preserved panarthropods from the Cambrian Lagerstätte of Sirius Passet, Greenland, including the soft‐bodied stem‐arthropod Pambdelurion whittingtoni and the hard‐bodied arthropods Kiisortoqia soperi and Campanamuta mantonae, are unique in preserving extensive musculature. Here we show that Pambdelurion's myoanatomy conforms closely to that of extant onychophorans, with unsegmented dorsal, ventral and longitudinal muscle groups in the trunk, and extrinsic and intrinsic muscles controlling the legs. Pambdelurion also possesses oblique musculature, which has previously been interpreted as an arthropodan characteristic. However, this oblique musculature appears to be confined to the cephalic region and first few body segments, and does not represent a shift towards arthropodan myoanatomy. The Sirius Passet arthropods, Kiisortoqia and Campanamuta, also possess large longitudinal muscles in the trunk, although, unlike Pambdelurion, they are segmentally divided at the tergal boundaries. Thus, the transition towards an arthropodan myoanatomy from a lobopodian ancestor probably involved the division of the peripheral longitudinal muscle into segmented units.     

Oceanic oxygenation events in the anoxic Ediacaran ocean

The ocean‐atmosphere system is typically envisioned to have gone through a unidirectional oxygenation with significant oxygen increases in the earliest (ca. 635 Ma), middle (ca. 580 Ma), or late (ca. 560 Ma) Ediacaran Period. However, temporally discontinuous geochemical data and the patchy metazoan fossil record have been inadequate to chart the details of Ediacaran ocean oxygenation, raising fundamental debates about the timing of ocean oxygenation, its purported unidirectional rise, and its causal relationship, if any, with the evolution of early animal life. To better understand the Ediacaran ocean redox evolution, we have conducted a multi‐proxy paleoredox study of a relatively continuous, deep‐water section in South China that was paleogeographically connected with the open ocean. Iron speciation and pyrite morphology indicate locally euxinic (anoxic and sulfidic) environments throughout the Ediacaran in this section. In the same rocks, redox sensitive element enrichments and sulfur isotope data provide evidence for multiple oceanic oxygenation events (OOEs) in a predominantly anoxic global Ediacaran–early Cambrian ocean. This dynamic redox landscape contrasts with a recent view of a redox‐static Ediacaran ocean without significant change in oxygen content. The duration of the Ediacaran OOEs may be comparable to those of the oceanic anoxic events (OAEs) in otherwise well‐oxygenated Phanerozoic oceans. Anoxic events caused mass extinctions followed by fast recovery in biologically diversified Phanerozoic oceans. In contrast, oxygenation events in otherwise ecologically monotonous anoxic Ediacaran–early Cambrian oceans may have stimulated biotic innovations followed by prolonged evolutionary stasis.     

Cerium negative anomaly just before the Permian and Triassic boundary event — The upward expansion of anoxia in the water column

A negative excursion of Ce and a succeeding steep decline in δ¹³C found just before the Permian and Triassic boundary (PTB) of Julfa area offer a geochemical constraint on the cause of the mass extinction event of PTB. The geochemical studies of recent anoxic basins like the Black Sea strongly suggest that the Ce negative excursion of these carbonate platform sequence indicates the buildup of anoxic water in the offshore realm. The suboxic water mass associated with the Ce negative anomaly zone migrated and invaded into shallow carbonate shelf around 600 thousand years before the PTB. This was followed by an anoxic water mass without Ce anomaly, and resulted in a steep decline in δ¹³C and then mass extinction of marine shelf biota.     

Hydrodynamics and sliding posture analysis of the Cambrian arthropod Ercaicunia multinodosa

Dynamic mechanical analysis offers the opportunity to explore the motility and feeding strategies of extinct organisms, but the prerequisite is to have an accurate recovery engineering model. As shown with micro-computed tomography (CT) scanning, fossils of the bivalved arthropod Ercaicunia multinodosa from the Cambrian (Series 2, Stage 3) Chengjiang biota of China have well-preserved three-dimensional (3D) morphological details with a certain degree of compression. Here, we propose a palaeontological restoration method using computational fluid dynamics (CFD) to analyse multiple hypothetical models based on the fossil information to obtain a reasonable restoration model. Furthermore, we carry out hydrodynamic experiments to verify the palaeontological restoration results. Our simulation and experimental results suggest that, a dorsally convex and ventrally straight body shape with the valves opening at an angle of approximately 120° works best for E. multinodosa to overcome resistance, and in the meantime obtain most lift while sliding in the water column. The combination of three-dimensional reconstruction, CFD simulation, and hydrodynamic experiments provides a useful method for restoring the morphologies of extinct animals and exploring their palaeoecology.     

Palaeoenvironmental reconstruction of Lower Toarcian epicontinental black shales (Posidonia Shale, SW Germany): global versus regional control

A detailed multidisciplinary investigation (sedimentology, palaeoecology, geochemistry) of the Lower Toarcian Posidonia Shale revealed that the depositional environment was mainly controlled by sea level changes and palaeoclimate. Carbon isotope values of both, carbonates and organic matter are closely related to environmental conditions. Highly unfavourable living conditions for benthic fauna prevailed during a relative sea level low stand resulting in an enclosed stagnant basin environment. Long-term benthic colonization could not occur until water circulation improved during sea level high stand. The carbon isotope record of the Posidonia Shale is primarily controlled by redox conditions. Due to the dependency of the isotopic composition on regional palaeoecological, sedimentological and geochemical conditions, on oxygen availability and sea level changes, there is no need to infer global atmospheric changes of pCO₂ or oceanwide anoxic events.     

Resolving Terreneuvian stratigraphy in subtidal–intertidal carbonates: palaeontological and chemostratigraphical evidence from the Turukhansk Uplift,Siberian Platform

Both diverse assemblages of small skeletal fossils and a representative chemostratigraphical record make the Siberian Platform widely regarded as one of the key regions for the reconstruction of global biotic and abiotic events in the late Ediacaran and early Cambrian. However, the wide distribution of intertidal–subtidal facies in the Ediacaran–Cambrian transitional strata of the central and southwestern Siberian Platform (Turukhansk–Irkutsk–Olekma facies region) produces a dramatic depletion of the palaeontological record and considerably limits their age‐calibration and long‐distance correlation. We report new lithological, palaeontological and carbonate carbon‐isotope data for the Ediacaran–Cambrian sections of the Turukhansk Uplift (northwestern Siberian Platform, western facies region). These data provide a robust framework for the chemostratigraphical correlation of the western facies region with sections of the transitional and eastern regions of the Siberian Platform and further confirms a depositional hiatus at the base of the Tommotian Stage in the stratotype section (Aldan River, SE Siberia). The carbon‐isotope curve from the Turukhansk Uplift sections correlates positively with the most chemostratigraphically representative Ediacaran–Cambrian sections (Siberia, Morocco, South China). It records major carbon‐isotope oscillations globally recognized in the lower Cambrian, enabling localization of the Fortunian and Cambrian Stage 2 boundaries in the Platonovskaya Formation. Although there is extreme paucity and poor preservation of the small skeletal fossils in the western facies region, we report individual Barskovia, Blastulospongia and chancelloriid sclerites from the Platonovskaya Formation. A combination of palaeontological and chemostratigraphical data suggests the base of P. antiqua Assemblage Zone is located in the middle Platonovskaya Formation. The earliest spiral gastropods probably occurred at ~541 Ma, as demonstrated by the discovery of a specimen of Barskovia near the base of the large negative excursion in the lower Platonovskaya Formation, correlated with the BACE negative carbon‐isotope peak in the sections of the Yangtze Platform.     

Feeding behaviour of a new worm (Priapulida) from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland (Laurentia)

Singuuriqia simoni gen. et sp. nov. represents the first record of a priapulid worm from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland (Laurentia). It is defined by an unusually broad, longitudinally folded, foregut which tapers through the pharynx towards the anterior mouth; posteriorly, the same longitudinal folding is evident in the narrow gut. The slender, smooth, trunk in the unique specimen passes anteriorly into an oval proboscis which culminates in a smooth, extensible, pharynx with pharyngeal teeth. The capacity for substantial expansion of the foregut permitted rapid ingestion of food prior to digestion at leisure. Cololites suggest both carnivorous and deposit feeding behaviour, indicating that Singuuriqia, like the present day Priapulus, was probably omnivorous.     

Effect of Hydrologic and Geochemical Conditions on Oxygen-Enhanced Bioremediation in a Gasoline-Contaminated Aquifer

Oxygen addition to enhance bioremediation of gasoline-contaminated ground water was performed in two locations of a shallow aquifer in South Carolina characterized by benzene, toluene, and methyl tert-butyl ether (MTBE) at concentrations greater than 1 mg/L, respectively. Oxygen addition with an oxygen-release compound (a proprietary form of magnesium peroxide [MgO₂]) produced markedly different results with respect to dissolved oxygen (DO) generation and contaminant decrease in the two locations. Oxygen-release compound injected at the former underground storage tank (UST) source area did not significantly change measured concentrations of DO, benzene, toluene, or MTBE. Conversely, oxygen-release compound injected 200 m downgradient of the former UST source area rapidly increased DO levels, and benzene, toluene, and MTBE concentrations decreased substantially. The different results can be related to differences in hydrologic and geochemical conditions that characterized the two locations prior to oxygen addition. For example, the contaminated aquifer downgradient of the former UST source area was anoxic, but frequently received oxygen-saturated recharge during rainfall events. As such, the aquifer was characterized by low concentrations of reduced species (such as ferrous iron (Fe²⁺), as well as relatively high numbers of aerobic heterotrophic bacteria (as most probable number [MPN] per milliliter). In contrast, recharge does not occur in the paved, former UST source area. The anoxic aquifer was characterized by higher concentrations of Fe²⁺ that exerted a significant chemical oxygen demand on the oxygen injected, and much lower numbers of aerobic heterotrophic bacteria. The results of this investigation indicate the important role that pre-existing hydrologic, geochemical, and microbiologic conditions have on the outcome of oxygen-based remediation strategies, and suggest that these properties should be evaluated prior to the implementation of oxygen-based remedial strategies.     

The mouth apparatus of the Cambrian gilled lobopodian Pambdelurion whittingtoni

Omnidens is a large feeding apparatus composed of circlets of teeth, first documented from the early Cambrian of China. Originally interpreted as the oral cone of a radiodontan, it was later reinterpreted as the introvert of a priapulan. In both cases the Omnidens mouthparts underpinned estimates of gigantic (c. 2 m) body size. Recent evidence has been used to suggest that pharyngeal teeth and radially‐arranged oral plates in the stem‐group onychophoran Hallucigenia and the lower stem‐group euarthropod Jianshanopodia are homologous to structures of the introvert in priapulans and other scalidophorans, and are thus primitive characters for moulting animals (Ecdysozoa) as a whole. Here we show that the early Cambrian gilled lobopodian Pambdelurion whittingtoni from Sirius Passet, Greenland, possesses a mouth apparatus identical to Omnidens, being composed of the same three zones with detailed similarities of sclerites in each zone. An oral cone with rings of pharyngeal teeth, radial plates and outer scalid‐like plates are ecdysozoan characters retained in the euarthropod stem group. Omnidens from China probably belongs to an unrecognized Pambdelurion‐like animal rather than being part of a giant priapulan.     

Distribution of iron in Lake Banyoles in relation to the ecology of purple and green sulfur bacteria

The distribution of iron both in suspended sediment and in the water column has been studied during summer stratification in Lake Banyoles. In this lake, near bottom springs, a very fine material suspended sediment remains in suspension. Dissolved Fe²⁺ in interstitial water of this suspended sediment, is related to redox potential and to the bottom water inflow. In the water column, soluble iron is present in the hypolimnion of the six different basins forming Lake Banyoles. Under those conditions Fe²⁺ is partially removed by sulfide produced in the anoxic sediment. In addition, a peak of Fe²⁺ found at the density gradient level in basins C-III, C-IV and C-VI. A three compartment model on the dynamics of the processes involving iron in Lake Banyoles is proposed. The bottom springs supply oxygen to the anoxic hypolimnion affecting chemical processes of the iron cycle. The presence of phototrophic sulfur bacteria in the anoxic monimolimnion of basins C-III and C-IV can be related to the kinetics of Fe²⁺ and sulfide. In C-III sulfide concentration exceeds Fe²⁺ concentration whereas in C-IV sulfide is not detectable and iron reached values up to 60 mM. The presence of phototrophic sulfur bacteria in iron-containing environments with no detectable sulfide is explained by the ability of such microorganisms to use FeS as electron donor instead of H₂S.     

An Early Cambrian stem polychaete with pygidial cirri

The oldest annelid fossils are polychaetes from the Cambrian Period. They are representatives of the annelid stem group and thus vital in any discussion of how we polarize the evolution of the crown group. Here, we describe a fossil polychaete from the Early Cambrian Sirius Passet fauna, Pygocirrus butyricampum gen. et sp. nov., with structures identified as pygidial cirri, which are recorded for the first time from Cambrian annelids. The body is slender and has biramous parapodia with chaetae organized in laterally oriented bundles. The presence of pygidial cirri is one of the characters that hitherto has defined the annelid crown group, which diversified during the Cambrian-Ordovician transition. The newly described fossil shows that this character had already developed within the total group by the Early Cambrian.