First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance

Abstract: Brachiopods are marine Lophotrochozoa whose soft parts are enclosed in a bivalved shell. Although brachiopods are represented by a rich record from the Early Cambrian to the present, the origin of their bivalved body plan remains controversial. The Early Cambrian organophosphatic tommotiids Micrina and Paterimitra from Australia have been proposed as stem brachiopods. Here, we describe their earliest ontogeny, indicating that tommotiids possessed bivalved planktotrophic larvae. The curious combinations of characters in Micrina and Paterimitra indicate that they may belong to the stems of the Linguliformea and Rhynchonelliformea, respectively. The bivalved shell of adult living brachiopods may represent a plesiomorphic character retained from planktic tommotiid larvae; the crown group body plan of the Brachiopoda may have evolved through the paedomorphic retention of a bivalved larval state.     

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.     

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.     

Problematic cap-shaped fossils from the Lower Cambrian of North-East Greenland

Three species ofOcruranus Liu, 1979 are described from the Bastion Formation of North-East Greenland, of late Early Cambrian (middle Dyeran of North American usage) age, representing the youngest record of a genus originally described from the earliest Cambrian Meishucunian Stage of China. An accompanying species, tentatively assigned toXianfengella He &Yang, 1982, seems also to be present in South Australia in strata of late Early Cambrian (Botoman of Siberian usage) age, although also this genus was described originally from the Meishucunian.Ocruranus andXianfengella from China have been interpreted as possibly parts of coeloscleritophoran scleritomes, perhaps halkieriids, rather than individual molluscan shells. Their shell form is not typical of helcionelloids which otherwise dominate the Early Cambrian molluscan record, but conclusive evidence of affinity is not forthcoming from the Greenland records. New taxa:Ocruranus septentrionalis n. sp. andOcruranus tunuensis n. sp.      

New data on molluscs and their shell microstructures from the Middle Cambrian Gowers Formation, Australia

Abstract: Numerous new cases of preserved shell microstructure were discovered in molluscs from the Middle Cambrian Gowers Formation (Ptychagnostus atavus/Peronopsis opimus Zone, Floran Stage) in the Georgina Basin, Australia. The new data provide further evidence that, by the Middle Cambrian, molluscan shell microstructures were diverse, and many molluscs had a complex shell with multiple types of shell microstructure. In addition, many new occurrences of laminar microstructures are described herein. For many, the nature of these laminar microstructures is not known, but in three species the microstructure is foliated calcite, and in at least two the microstructure is more likely to have been calcitic semi‐nacre, a type of microstructure known in brachiopods and bryozoans but unknown in modern molluscs. This commonality among these three closely related lophotrochozoans underscores a similar mechanism of biomineralization. Moreover, these observations suggest a prevalence of calcite‐shelled lineages among molluscs from the Middle Cambrian, a time of calcite seas. In addition, the broad occurrence of laminar, nacre‐like microstructures in many of these fossils reveals how widespread these strong (fracture‐resistant) microstructures were in Middle Cambrian molluscs. Additionally, a few specimens of Yochelcionella preserve imprints of a bilaterally symmetrical pair of muscle scars. New taxa described here include Corystos thorntoniensis gen. et sp. nov., Yochelcionella snorkorum sp. nov., Yochelcionella saginata sp. nov., and Anhuiconus? agrenon sp. nov.     

The brachiopod <Emphasis Type="Italic">Eoobolus</Emphasis> from the Early Cambrian Mural Formation (Canadian Rocky Mountains)

The Early Cambrian brachiopod, Eoobolus, is one of the first representatives of the superfamily, Linguloidea, the defining characteristics of which include the classical morphology of oval shells and a pedicle that emerges from between the two valves. The material described here from the Mural Formation (Jasper National Park, Canadian Rocky Mountains) provides well-preserved muscle scars and larval shells that allow a discussion of the muscle system and the larval morphology of Eoobolus. The dorsal larval shell exhibits a morphology similar to other Cambrian linguloids, but also to paterinids, Mickwitzia muralensis, and some rhynchonelliforms. This suggests that there was a lesser degree of disparity among brachiopod larvae in the Cambrian than there is today. The muscle system of Eoobolus is similar to other linguloids, but differs from that of Recent lingulids and discinids by having one or two more pairs of oblique muscles. New data on the distribution of features characteristic of the family Eoobolidae question the validity of this family.     

峡东地区寒武纪水井沱组下段双瓣壳类节肢动物系统古生物与个体发育研究

双瓣壳类节肢动物在全球寒武纪海洋中广泛分布,是寒武纪时期布尔吉斯页岩型化石生物群的重要组成类群和典型代表。它们的起源、演化及生态学研究是对早期后生动物演化研究的重要内容。本文详细描述了峡东地区寒武系第二统第三阶水井沱组下段两种双瓣壳类节肢动物,Caudicaella bispinata (Cui and Huo,1990) comb.nov.和Sunella grandis Huo,1965。依据新建的Caudicaella属征,对孙氏虫科的鉴定特征进行了修订。首次研究了孙氏虫科两属种壳瓣的生长发育模式,揭示了壳瓣高长比的等速生长和C.bispinata基刺相对于壳长的异速生长关系。元素扫描分析研究表明,长阳地区天柱山村剖面化石为碳质压膜保存。功能形态学研究认为,C.bispinata是远洋浮游型生物,其广泛的古地理分布有望为寒武纪早期全球生物地层对比提供新的化石依据。     

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。     

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。     

New data on the morphology of ancient gastropods of the genus Aldanella Vostokova, 1962 (Archaeobranchia, Pelagielliformes)

The position of attachment of the shell muscle is discovered in the columellar area of the shell of the Early Cambrian univalved genus Aldanella (family Aldanellidae, order Pelagielliformes, subclass Archaeobranchia), the structure of its protoconch is described, and the presence of series of septa in the embryonic part of their shell is confirmed. These new features confidently support the position of the family Aldanellidae within the gastropod class and allow them to be considered ancestral to younger gastropod lineages with a turbospiral shell.     

A new early Cambrian bivalved euarthropod from Yunnan,China and general interspecific morphological and size variations in Cambrian hymenocarines

The hymenocarines were a major and diverse group of euarthropods featured by a bivalved head carapace and a segmented trunk comprising tergo-pleural rings notably from the Cambrian Burgess Shale-type Lagerstätten. Here we document a new ~50 mm long hymenocarine Xiazhuangocaris chenggongensis n. gen. n. sp. from the Xiazhuang fossil assemblage, a slightly younger occurrence of the Chengjiang Lagerstätte within the lower Cambrian Hongjingshao Formation (Cambrian Series 2, Stage 3) in Chenggong, Yunnan, southwestern China. X. chenggongensis is characterized by the bivalved carapace with each valve bearing a protruded anterior tip and a prominent posterior notch, which resembles the P-element of the radiodont Hurdia and is unique among the hymenocarines. The trunk consists of at least 13 tergo-pleural rings including presumably eight abdominal ones terminating in a pair of ovate caudal rami. With the body organization and morphological features closest to waptiids, X. chenggongensis represents a ‘larger’ waptiid-like hymenocarine. The morphometric analysis recognizes the family-level groupings of Cambrian hymenocarines based on the number of tergo-pleural rings and the proportion of exposed trunk length, indicating that these are useful characters for studying hymenocarine morphology and phylogeny. Cambrian hymenocarines exhibited great interspecific body size variations even between sister species of the same family, further suggesting that niche diversification happened on the family level and even among phylogenetically close genera or species during the Cambrian explosion.     

A new mobergellan (small shelly fossils) from the early middle cambrian of morocco and its significance

A new mobergellan genus and species,Tateltella ranoculata, is described from the early Middle Cambrian (Agdzian Stage) of Morocco. The new taxon is characterized by only four pairs of muscle scars and is furthermore distinguished from other mobergellans by its strongly concave shape and its distally rising muscle scars. The individual specimens ofTateltella ranoculata distinctly vary in size and display different ontogenetic stages. Juvenile, intermediate, and adult stages can be distinguished by means of the development of the muscle scars that differ in Position relative to the apex, size, and distinctness between individual stages. The shell ofT. ranoculata is composed of a succession of thin phosphatic lamellae separated by interlamellar gaps, presumably originally filled by organic material. The interlamellar gaps may be divided by septum-like structures producing discrete cavities. The specimens are the youngest mobergellans known so far and correlation of their stratigraphic position suggests a correspondence with the lower part of the Amgan stage of the Siberian Platform. In addition, they are the first reported mobergellans from the present day continent Africa. Other mobergellan taxa and mobergellan-like species are briefly reviewed and the genusHippoklosma Missarzhevsky, previously assigned to the Mobergellidae, is excluded from the family due to its different shell structure. An evolutionary trend of reduction in the number of muscle scars from 14 in the early Early Cambrian to only eight in the early Middle Cambrian is apparent among mobergellans.      

Revision of the superfamily Acrotheloidea (Brachiopoda,class Linguliformea,order Lingulida) from the Lower and Middle Cambrian of the Siberian Platform

This paper continues our revision of Yu.L. Pelman’s collection of the superfamily Acrotheloidea (phosphatic brachiopods) and of our own material from the Early–Middle Cambrian of the Siberian Platform. The following representatives of the superfamily Acrotheloidea (order Lingulida, class Linguliformea) are restudied and revised based on new techniques: the genus Botsfordia (family Botsfordiidae Schindewolf, 1955) and the genera Acrothele, Eothele, and Orbithele (family Acrothelidae), which are widespread on the Siberian Platform. Only one out of the three Acrothele species described by Pelman is recognized as a valid species, and one new species of this genus that comprises some part of the brachiopods that Pelman figured and placed in another taxon is described. All these species are described using data on shell microsculpture and microstructure. In addition, the genera Eothele and Orbithele are described for the first time from the Siberian Platform.     

Muscle scars, shell form and torsion in Cambrian and Ordovician univalved molluscs

Runnegar, Bruce 1981 12 15: Muscle scars, shell form and torsion in Cambrian and Ordovician univalved molluscs. Lethaia, Vol. 14, pp. 311–322. Oslo. ISSN 0024–1164. Well preserved muscle scars have been discovered on one or more specimens of the early Palaeozoic univalved molluscs Pelagiella, Matherella, Sinuites and ?Bucania. From this information it is argued that the bellerophonts Sinuites and ?Bucania were untorted, that Pelagiella had undergone about 10° of torsion, and that Matherella may have been a fully torted, hyperstrophic descendant of Pelagiella. Other early gastropods such as Aldanella could have been independently derived from Pelagiella and therefore the Class Gastropoda may be at least diphyletic. In general, small dextrally coiled archaeogastropods such as Aldanella and the pelagiellids are the most common asymmetrical univalves of the Early Cambrian, but rare ultradextral (hyperstrophic) forms are also known. Only pelagiellids are known from the Middle Cambrian, and ultradextral forms dominate in the Late Cambrian. As a result, slit-bearing archaeogastropods are not common before the Ordovician. Yuwenia bentleyi gen. et sp. nov. is a new taxon proposed in this work. *Mollusca, Gastropoda, Monoplacophora, anatomy, evolution, Cambrian, Ordovician, Yuwenia n.g.     

黔东寒武纪凯里生物群中腕足动物主导的群落生态研究*

寒武纪大爆发时期, 以动物为主导的海洋生态系统已初步构建完成。腕足动物作为这一时期海生底栖群落的重要代表, 建立了复杂的多层次生态分层(Tiering)结构。华南寒武纪一些特异埋藏化石群中出现大量单属种腕足动物壳体富集保存的现象, 对当时海洋底质的硬化改造以及生态系统的复杂化发挥了重要意义。黔东剑河革东地区苗板坡、金银山和承多三个剖面的凯里生物群(寒武纪乌溜期)中普遍产出腕足动物化石密集层, 其中以舌形贝型亚门(Linguliformea)的伯瑞堂古圆货贝(Palaeobolus bretonensis)占据绝对主导地位。此外, 密集层中还有较多的古盘虫类三叶虫、少量蠕形动物、软体动物和始海百合等底栖生物共同保存。研究显示, 凯里生物群中腕足动物密集层内的化石保存较好, 几乎全部平行于层面保存, 壳体大小不一, 无明显定向性, 判断为生物成因的原地埋藏群落。化石层面和岩石光面显示, 除了微弱的水平层理, 密集层未见其他强水动力的沉积构造和生物扰动痕迹, 指示凯里生物群中以腕足动物为主导的生物群落可能在安静的水体环境中被沉积事件原地掩埋, 未遭受流体侵蚀或搬运作用。通过建立生态结构理论模型和对比分析, 显示凯里生物群中腕足动物主导的古群落在物种多样性和生态空间利用率方面都要高于滇东寒武纪第四期的关山生物群。同时, P. bretonensis壳体上固着有始海百合动物, 可能反映密集层中复杂的底栖群落关系, 表明寒武纪乌溜期大量繁盛的带壳腕足动物为泥质软基底上的底栖生物提供了更多生态空间。     

Early Late Cambrian Trilobites OF Australo-Sinian Aspect From The Montagne Noire, Southern France

Ten species of Late Cambrian trilobites occur in a limestone lens at the base of the Val d'Homs Formation in the Cesse Brook section at Ferrals‐les‐Montagnes in the Montagne Noire. Associated in this lens are species referred to Ammagnostus (Ammagnostus), Kormagnostus?, Olentella, Stigmatoa, Shengia, Abharella, Proceratopyge, (Proceratopyge), ProchuangiaPalaeadotes and Paraacidaspis. Of these, Stigmatoa courtessolei and Paraacidaspis ultima are described as new species. The Ferrals fauna has a decidedly Australo‐Sinian palaeobiogeographical relationship, with the implication that previously developed models suggesting a high latitudinal position for southern France during the Late Cambrian should perhaps be revised. key words : Late Cambrian, trilobites, southern France, Ferrals‐les‐Montagnes, Montagne Noire, biostratigraphy, biogeography.     

New and poorly known acrotretid brachiopods (Class Lingulata) from the Cedaria-Crepicephalus zone (late Middle Cambrian) of the Great Basin, USA

Seven new late Middle Cambrian (Cedaria-Crepicephalus zone) acrotretid species are described from the Great Basin, USA. The species belong to five genera of which Lensotreta is new. The following new species are described: Anabolotreta? glabra, Anabolotreta mogota, Canthylotreta crista, Dactylotreta elegantula, Lensotreta perplexa, Opisthotreta transversa, and Opisthotreta indistincta. The shell structure of Canthylotreta is described for the first time based on new material of the type species Canthylotreta marjumensis and of the new species C. crista. The shell of Canthylotreta includes two types of shell fabric, camerate and columnar. Moreover, parts of the shell show transitional textures, supporting the view that the camerate shell structure may has originated from a columnar fabric. Picnotreta lophocracenta Robson and Pratt, 2001, recently described from western Newfoundland, is also described from the new occurrence in the Great Basin.     

New data on the enigmatic Ocruranus–Eohalobia group of Early Cambrian small skeletal fossils

Abstract: The Ocruranus–Eohalobia group, whose members were variously considered to be brachiopods, bivalves, chitons, tommotiids and coeloscleritophorans, are difficult to classify because of lack of morphological detail and evidence for skeletal reconstruction. New specimens from South China reveal more information about Ocruranus–Eohalobia and allow progress towards deciphering the skeletal reconstruction and phylogenetic affinity of this enigmatic group. Many specimens have a phosphatic inner and outer coat (mould) with empty space in between that resulted from dissolution of the original shell. Moreover, many of the internal moulds show a previously unknown type of shell microstructure that consisted of stacked layers of highly organized, acicular crystallites that radiated from the apex of the shell towards the aperture. The dissolved shell and needle‐like crystals suggest an original calcareous, probably aragonitic, shell mineralogy. A few specimens also show a polygonal texture in regions that suggests the shell had a thin, prismatic inner shell microstructure. Ocruranus and Eohalobia belong to the same skeleton, and we herein synonymize Eohalobia with the older Ocruranus. Moreover, new specimens from Meishucun reveal a third type of shell plate, similar in form and inferred placement to intermediate valves of chitons. Ocruranus is likely a mollusc, and possibly a member of the chiton stem lineage. If so, then the beginning of the known record of chitons would be extended back from late Cambrian (Saukia Zone; Furongian) to early Cambrian (Meishucunian; Series 1).     

Lower Cambrian (Botomian) polycystine Radiolaria from the Altai Mountains (southern Siberia, Russia)

Relatively well-preserved polycystine Radiolaria are here described from Lower Cambrian (Botomian) strata of the Shashkunar Formation, Altai Mountains in southern Siberia (Russia). These radiolarians display a test formed of a disorderly and three-dimensionally interwoven meshwork of numerous straight and curved bars branching from a five-rayed point-centered spicule located within the inner shell surface. The shell structure allows their assignment to the family Archeoentactiniidae, thus extending the known age range of the family down to the Lower Cambrian. The Botomian age is based essentially on trilobites (Parapagetia-Serrodiscus zone), but also on archaeocyathids identified in earlier publications. The study of the radiolarian-bearing sedimentary sequence confirms the presence of polycystine radiolaria in the external platform environments of Lower Cambrian ecosystems.