Anatomy and lifestyles of Early Cambrian priapulid worms exemplified by Corynetis and Anningvermis from the Maotianshan Shale (SW China)

Accurate information on the anatomy and ecology of worms from the Cambrian Lagerstätten of SW China is sparse. The present study of two priapulid worms Anningvermis n. gen. and Corynetis Luo & Hu, 1999 from the Lower Cambrian Maotianshan Shale biota brings new information concerning the anatomical complexity, functional morphology and lifestyles of the Early Cambrian priapulids. Comparisons are made with Recent priapulids from Sweden (live observations, SEM). The cuspidate pharyngeal teeth of Anningvermis (circumoral pentagons) and the most peculiar radiating oral crown of Corynetis added to the very elongate pharynx of these two forms are interpreted as two different types of grasping apparatus possibly involved in the capture of small prey. Corynetis and Anningvermis are two representative examples of the Early Cambrian endobenthic communities largely dominated by priapulid worms (more than ten species in the Maotianshan Shale biota) and to a much lesser extent by brachiopods. Corynetis and Anningvermis were probably active mud-burrowers and predators of small meiobenthic animals. Likewise predator priapulid worms exploited the interface layer between the seawater and bottom sediment, where meiobenthic organisms were abundant and functioned as prey. This implies that complex prey-predator relationship between communities already existed in the Early Cambrian. This study also shows that the circumoral pentagonal teeth and caudal appendage were present in the early stages of the evolutionary history of the group and were important features of the priapulid body plan already in the Early Cambrian. Two new families, one new genus and new species are introduced and described in the appendix.     

A death assemblage of priapulid worms from the Middle Cambrian Burgess Shale

A slab of Burgess Shale (Middle Cambrian), displaying an incomplete exoskeleton of the large arthropod Sidneyia inexpectans and encompassed by nine specimens of the priapulid worm Ottoia prolifica, is interpreted as a death assemblage, with the worms once living off or feeding around a carcass or freshly moulted instar of Sidneyia. Death is thought to have been caused by an obrution event that preserved the organisms in situ.     

The feeding behaviour of the Cambrian tubiculous priapulid Selkirkia

Feeding behavioural patterns have the potential to shed light on evolutionary trends, especially at the critical point of the Cambrian Explosion. In this context, we present specimens of the tubiform priapulid Selkirkia sinica, preserved in situ, collected from the lower Cambrian (Stage 3) Xiaoshiba Lagerstätte, which show the diverse morphology of its intestinal contents within the dark‐coloured gut and the formation of faecal pellets. The two digestive modes displayed by S. sinica suggest that it is a putative dietary generalist rather than a typical scavenger as previously thought. Moreover, the asymmetry exhibited by the paired caudal appendages of S. sinica provides direct evidence of the development of dorsoventral (DV) differentiation in Selkirkia, which aids our understanding of the lifestyle of this tubiculous worm.     

Thecate stem medusozoans (Cnidaria) from the early Cambrian Chengjiang biota

Cnidarians are phylogenetically located near the base of the ‘tree of animals’, and their early evolution had a profound impact on the rise of bilaterians. However, the early diversity and phylogeny of this ‘lowly’ metazoan clade has hitherto been enigmatic. Fortunately, cnidarian fossils from the early Cambrian could provide key insights into their evolutionary history. Here, based on a scrutiny of the purported hyolith Burithes yunnanensis Hou et al. from the early Cambrian Chengjiang biota in South China, we reveal that this species shows characters distinct from those typical of hyoliths, not least a funnel-shaped gastrovascular system with a single opening, a whorl of tentacles surrounding the mouth, and the lack of an operculum. These characters suggest a great deviation from the original definition of the genus Burithes, and a closer affinity with cnidarians. We therefore reassign the material to a new genus: Palaeoconotuba. Bayesian inference of phylogeny based on new anatomical traits identifies a new clade, including Palaeoconotuba and Cambrorhytium, as a stem group of sessile medusozoan cnidarians that are united by the synapomorphies of developing an organic conical theca and a funnel-like gastrovascular system. This study unveils a stem lineage of medusozoans that evolved a lifelong conical theca in the early Cambrian.     

Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan

Research into arthropod evolution is hampered by the derived nature and rapid evolution of the best-studied out-group: the nematodes. We consider priapulids as an alternative out-group. Priapulids are a small phylum of bottom-dwelling marine worms; their tubular body with spiny proboscis or introvert has changed little over 520 million years and recognizable priapulids are common among exceptionally preserved Cambrian fossils. Using the complete mitochondrial genome and 42 nuclear genes from Priapulus caudatus, we show that priapulids are slowly evolving ecdysozoans; almost all these priapulid genes have evolved more slowly than nematode orthologs and the priapulid mitochondrial gene order may be unchanged since the Cambrian. Considering their primitive bodyplan and embryology and the great conservation of both nuclear and mitochondrial genomes, priapulids may deserve the popular epithet of "living fossil." Their study is likely to yield significant new insights into the early evolution of the Ecdysozoa and the origins of the arthropods and their kin as well as aiding inference of the morphology of ancestral Ecdysozoa and Bilateria and their genomes.     

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.     

The disparity of priapulid, archaeopriapulid and palaeoscolecid worms in the light of new data

Priapulids and their extinct relatives, the archaeopriapulids and palaeoscolecids, are vermiform, carnivorous ecdysozoans with an armoured, extensible proboscis. These worms were an important component of marine communities during the Palaeozoic, but were especially abundant and diverse in the Cambrian. Today, they comprise just seven genera in four families. Priapulids were among the first groups used to test hypotheses concerning the morphological disparity of Cambrian fossils relative to the extant fauna. A previous study sampled at the generic level, concluding that Cambrian genera embodied marginally less morphological diversity than their extant counterparts. Here, we sample predominantly at the species level and include numerous fossils and some extant forms described in the last fifteen years. Empirical morphospaces for priapulids, archaeopriapulids and palaeoscolecids are relatively insensitive to changes in the taxon or character sample: their overall form has altered little, despite the markedly improved sampling. Cambrian and post-Cambrian genera occupy adjacent rather than broadly overlapping regions of these spaces, and Cambrian species still show lower morphological disparity than their post-Cambrian counterparts. Crucially, the significance of this difference has increased with improved taxon sampling over research time. In contrast with empirical morphospaces, the phylogeny of priapulids, archaeopriapulids and palaeoscolecids derived from morphological characters is extremely sensitive to details of taxon sampling and the manner in which characters are weighted. However, the extant Priapulidae and Halicryptidae invariably resolve as sister families, with this entire clade subsequently being sister group to the Maccabeidae. In our most inclusive trees, the extant Tubiluchidae are separated from these other living taxa by a number of small, intervening fossil clades.     

An early Cambrian chelicerate from the Emu Bay Shale,South Australia

The Emu Bay Shale Lagerstätte (Cambrian Series 2, Stage 4) occurs on the north coast of Kangaroo Island, South Australia. Over 50 species are known from here, including trilobites and non‐biomineralized arthropods, palaeoscolecids, a lobopodian, a polychaete, vetulicolians, nectocaridids, hyoliths, brachiopods, sponges and chancelloriids. A new chelicerate, Wisangocaris barbarahardyae gen. et sp. nov., is described herein, based on a collection of some 270 specimens. It is up to 60 mm long, with the length of the cephalic shield comprising about 30% that of the exoskeleton. The cephalic margin has three pairs of bilaterally‐symmetrical small triangular spines. A pair of small eyes is placed well forwards on the ventral margin of the cephalic shield. The trunk comprises 11 segments that increase in length while narrowing posteriorly, each possibly bearing a pair of biramous appendages; the most posterior segment is almost square whereas the others are transversely elongated. The spatulate telson is proportionately longer than in taxa such as Sanctacaris, Utahcaris and Leanchoilia. Up to eight (?four pairs) of 3 mm‐long elements bearing alternating inward‐curving short and long spines beneath the cephalic shield are interpreted as basipodal gnathobases, part of a complex feeding apparatus. A well‐developed gut includes a stomach within the cephalic shield; it extends to the base of the telson. In a few specimens there are shell fragments within the gut, including those of the trilobite Estaingia bilobata (the most common species in the biota); these fragments have sharp margins and extend across the gut lumen. The species may have been a predator or a scavenger, ingesting material already broken up by a larger predator/scavenger. The morphology of this taxon shares many overall body features with Sanctacaris, and some with Sidneyia, particularly its gnathobasic complex. These chelicerate affinities are corroborated by phylogenetic analyses.     

Predation by early Cambrian trilobites on infaunal worms - evidence from the Swedish Mickwitzia Sandstone

Evidence of early Cambrian predation is found in trace fossils from the Mickwitzia Sandstone of VastergÖtland, Sweden. The arthropod burrow Rusophycw dispar was dug down to spreite burrows in such a manner that mere coincidence of place is unlikely. The predator is identified as an olenellacean trilobite, mainly through the presence of a cephalic impression. The prey, a worm that may have been a priapulid, was localized visually or chemically at the spreite-burrows apertures. The predator lacked legs specialized for seizing prey, as indicated by the parallel, but laterally displaced position of the Rusophycus above the spreite burrow. In this stance prey could be gripped by flexing the supposedly spinose legs of one side around it. When a spreite burrow of limited horizontal extension was encountered, parallel orientation was obtained prior to digging, probably through chemical sensing, whereas parallel orientation to an extended burrow required a number of diggings. These traces are important evidence of early Cambrian predation and of the predatorial capability of trilobites. □ Lower Cambrian, Sweden predation, trilobites, priapulids , Rusophycus.     

寒武纪早期宽川铺生物群中圆管螺化石显微结构及显微谱学分析

陕南寒武系底部宽川铺组不仅保存了大量的小壳化石,还以磷酸盐化的方式立体保存了多种软躯体动物的胚胎和成体化石,为研究早期动物矿化模式、个体发育方式以及动物躯体构型的早期辐射过程提供了非常关键的信息。然而宽川铺生物群的研究大多聚焦于化石系统分类及亲缘关系探索,对生物群的沉积背景、埋藏过程和保存模式的分析甚少。本文以宽川铺生物群的核心产出层位——陕西省西乡县大河镇宽川铺组下部磷质碎屑灰岩为研究对象,对其中的一类管状化石圆管螺及其围岩进行了显微结构学和显微谱学综合分析,获得了化石显微结构和关键结构对应的元素、矿物成分等信息,讨论了管状化石圆管螺的埋藏过程和保存模式,并在此基础上对其生物学特征进行了初步探讨。该研究对理解宽川铺生物群的埋藏机制提供了新的线索。     

Disparity, decimation and the Cambrian "explosion": comparison of early Cambrian and present faunal communities with emphasis on velvet worms (Onychophora)

The controversy about a Cambrian "explosion" of morphological disparity (followed by decimation), cladogenesis and fossilization is of central importance for the history of life. This paper revisits the controversy (with emphasis in onychophorans, which include emblematic organisms such as Hallucigenia), presents new data about the Chengjiang (Cambrian of China) faunal community and compares it and the Burgess Shale (Cambrian of Canada) with an ecologically similar but modern tropical marine site where onychophorans are absent, and with a modern neotropical terrestrial onychophoran community. Biovolume was estimated from material collected in Costa Rica and morphometric measurements were made on enlarged images of fossils. Cambrian tropical mudflats were characterized by the adaptive radiation of two contrasting groups: the vagile arthropods and the sessile poriferans. Arthropods were later replaced as the dominant benthic taxon by polychaetes. Vagility and the exoskeleton may explain the success of arthropods from the Cambrian to the modern marine and terrestrial communities, both in population and biovolume. Food ecological displacement was apparent in the B. Shale, but not in Chengjiang or the terrestrial community. When only hard parts were preserved, marine and terrestrial fossil deposits of tropical origin are even less representative than deposits produced by temperate taxa, Chengjiang being an exception. Nutrient limitations might explain why deposit feeding is less important in terrestrial onychophoran communities, where carnivory, scavenging and omnivory (associated with high motility and life over the substrate) became more important. Fossil morphometry supports the interpretation of "lobopod animals" as onychophorans, whose abundance in Chengjiang was equal to their abundance in modern communities. The extinction of marine onychophorans may reflect domination of the infaunal habitat by polychaetes. We conclude that (1) a mature ecological community structure was generalized during the Cambrian, and even biodiversity and equitability indices were surprisingly close to modern values; (2) the morphological diversity and geographic distribution of onychophorans indicate a significant pre-Cambrian evolutionary history which does not support the "explosion" hypothesis; (3) disparity among phyla was not as important as the explosion-decimation model predicts, but in the case of onychophorans, disparity within the phylum was greater than it is today and its reduction may have been associated with migration into the sediment when large predators evolved.     

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.     

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.     

Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale

The fossil record plays a key role in reconstructing deep evolutionary relationships through its documentation of the early diverging stem groups leading to extant phyla. In the middle Cambrian Burgess Shale, two famously problematic worms, Odontogriphus and Wiwaxia, have recently been reinterpreted as stem-group molluscs based on their shared expression of a putative radula and putative ctenidia in Odontogriphus. More detailed analysis of these fossil structures, however, reveals pronounced anatomical and histological discrepancies with molluscan analogues, such that they are more reliably interpreted as primitive features of the superphylum Lophotrochozoa. In the absence of any obviously derived characters, Odontogriphus could be placed in the stem group of the Lophotrochozoa or on the stem of any of its constituent phyla, whereas the dorsal covering of chaetae in Wiwaxia identifies it as a stem-group polychaete. Despite their close relationship, these two jawed, segmented worms could conceivably represent the early stages of two separate phyla.     

Early Cambrian origin of modern food webs: evidence from predator arrow worms

Although palaeontological evidence from exceptional biota demonstrates the existence of diverse marine communities in the Early Cambrian (approx. 540-520 Myr ago), little is known concerning the functioning of the marine ecosystem, especially its trophic structure and the full range of ecological niches colonized by the fauna. The presence of a diverse zooplankton in Early Cambrian oceans is still an open issue. Here we provide compelling evidence that chaetognaths, an important element of modern zooplankton, were present in the Early Cambrian Chengjiang biota with morphologies almost identical to Recent forms. New information obtained from the lowermost Cambrian of China added to previous studies provide convincing evidence that protoconodont-bearing animals also belonged to chaetognaths. Chaetognaths were probably widespread and diverse in the earliest Cambrian. The obvious raptorial function of their circumoral apparatuses (grasping spines) places them among the earliest active predator metazoans. Morphology, body ratios and distribution suggest that the ancestral chaetognaths were planktonic with possible ecological preferences for hyperbenthic niches close to the sea bottom. Our results point to the early introduction of prey-predator relationships into the pelagic realm, and to the increase of trophic complexity (three-level structure) during the Precambrian-Cambrian transition, thus laying the foundations of present-day marine food chains.     

节肢动物吐卓虫咬痕化石在云南昆明附近寒武纪早期关山生物群的发现及意义*

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

Ecological integrity of supraspecific taxa and the arctic biota

Some specific features of the development of concepts about integrity (systemic organization) of supraspecific taxa are considered. Several forms of integrity can be distinguished: taxonomic, or genealogical; evolutionary (considering a taxon as a developing system); ecological, or eco-adaptive (manifestation of the properties of a united system in the course of exploring the various conditions and types of environment by the phyletically specified biota). Taxa of different level “behave” as whole units or blocks, forming structural parts of the cenotic and biotic forms of life. The properties of integrity, systemic organization of supraspecific taxa can be displayed by analysis of changes in the structural parameters of the biota related to latitudinal gradients of climatic factors, in phenomena of individualistic distribution, ecological substitution (vicariance) of taxa, and preservation of their ecological functions (adaptive zone) despite the reduced species diversity. The variants of adaptive exploration of high-latitude landscape-zonal conditions are considered using examples from the Arctic flora and fauna.     

节肢动物吐卓虫咬痕化石在云南昆明附近寒武纪早期关山生物群的发现及意义*

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

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.