The soft anatomy of Isoxys minor from the Guanshan fauna,lower Cambrian of Southwest China

Isoxys is a very common Cambrian bivalved arthropod, specimens of which are normally preserved only as valves. The discovery of the soft anatomy of Isoxys may greatly assist understanding affinities and functional morphology. Isoxys minor Luo and Hu in Luo et al., 2008 is the most common representative of all animal species known from the lower Cambrian Guanshan fauna (Cambrian Series 2, Stage 4) at the Shitangshan Section, near Kunming, Yunnan Province, Southwest China. Here we describe and reconstruct the morphology of I. minor on the basis of newly illustrated fossils and a few new specimens that bear soft-parts including new discovery of frontal grasping appendages. Like the soft anatomy of other known Isoxys, it bears a pair of large stalked eyes, a pair of specialized frontal grasping appendages, approximately 12–14 paired biramous limbs, and a helm-like tail exposed outside the valves.     

Scleritome construction,biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia

Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap‐shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap‐shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap‐shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath‐microbial‐spongiomorph‐dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca‐like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to ‘E.’guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and ‘E.’guano belong to the same scleritome.     

贵州剑河寒武系苗岭统凯里组太阳女神螺类几何形态学研究*

太阳女神螺类(helcionellids)是寒武纪常见的一类软体动物,广布全球,多见于碳酸盐岩沉积地层中,而布尔吉斯页岩型生物群中却少有报道。贵州剑河凯里生物群是典型的特异埋藏化石库,产有700余件太阳女神螺类标本,这在世界各地同时期的布尔吉斯页岩型生物群中是很少见的。本文对贵州剑河八郎寒武系凯里组太阳女神螺类化石标本进行了系统研究,采用几何形态测量学的典型变量分析进行量化分析。几何形态测量学(Geometric morphometrics)是用界标点或轮廓线等来描绘生物的形态或者标记特征部位及器官,将生物形态特征归纳为数据变化的定量学方法,其中的典型变量分析(Canonical Variate Analysis)是多变量分析中进行判别分析的一个重要方法,可以用于多组数据之间的判别。CVA判别结果显示:利用壳体侧视轮廓线判别Dorispira属中三个种的正确率为92%,验证了Dorispira accordinonata、D.taijiangensis和D.cf.pearylandica化石种分类合理性。本文研究表明即使壳体形态较为相似的类群,也可以较为准确地使用CVA量化其中的差别,...     

A first report of Sphenothallus Hall, 1847 in the Cambrian of Variscan Europe

Ten specimens of two phosphatic fossils have been recently discovered in lower and middle portions of Middle Cambrian Jince Formation in the Czech Republic. They are attributed to the genus Sphenothallus Hall, 1847 and described as two separate species; comparatively small conchs are described as S. kozaki sp. nov., the much larger specimens characterized by its smooth and partly flexible organo-phosphatic walls of shell are determined as ?S. kordulei sp. nov. Sphenothallus is known to range from Cambrian to Permian and accommodates numerous species. However, its Cambrian distribution is considerably restricted. Generally rare specimens have been described from Lower to Middle Cambrian of Laurentia and from the Lower Cambrian of Gondwana and peri-Gondwana. The new record of Sphenothallus from the Jince Biota represents a notable extension of their geographic range.     

Occurrence ofByronia Matthew andSphenothallus Hall in the Lower Cambrian of China

Rare phosphatic tubular fossils from the Lower-Middle Cambrian Kaili Formation of Guizhou Province, southern China were originally identified as non-calcified algae or ‘worms’ (ScoleciellusLiu). Re-examination of these fossils indicates that specimens identified as non-calcified algae areSphenothallus taijiangensis n. sp., while specimens identified asScoleciellus belong toByronia natus (Liu).Sphenothallus taijiangensis andByronia natus from Lower Cambrian strata in the Kaili Formation are the oldest known representatives of their genera. In addition,B. natus (Liu) is the only known species ofByronia with the exception ofB. annulata Matthew (Middle Cambrian, British Columbia). CambrovitusMao et al., a tubular fossil from Middle Cambrian strata in the Kaili Formation, originally was classified as a hyolithid. However, the discovery of a nearly complete specimen possessing an apical attachment disk shows thatCambrovitus, likeByronia andSphenothallus, probably was a thecate cnidarian polyp.     

A new rhynchonelliform brachiopod Longtancunella with soft-part preservation from the Hongjingshao Formation (Cambrian Stage 3) in Yunnan,South China

Rhynchonelliform brachiopods made their first appearance in early Cambrian, and became a major group within the palaeozoic evolutionary fauna since late Cambrian. Exceptionally preserved fossils from the early Cambrian Lagerstätten provide valuable chances to investigate their phylogeny and ecology. Longtancunella is one of the most interesting early rhynchonelliforms, and has been mainly recovered from the Chengjiang Lagerstätte (Series 2, Stage 3). Here, we report a new rhynchonelliform Longtancunella xiazhuangensis n. sp. from the lower Hongjingshao Formation (upper Stage 3) in Yunnan Province, China. These specimens were well preserved with soft parts, including pinnate mantle canal system and a pedicle. It is identified as a new species based mainly on its difference in shell ornamentations, pinnate mantle canals and pedicle morphology from the type species. Its pedicle looks unusually stout with distinct annulated lamellae on the surface, and reveals crucial evidence in illustrating its ecology and settling strategy as an early marine epifauna. The ecological interaction between L. xiazhuangensis and other marine animals also provides insights into the food web structure in the early Cambrian.     

New bradoriids from the Lower Cambrian Yanwangbian formation of southern Shaanxi Province,Central China

Located in the northwest margin of the South China Block during the Cambrian, the Lower Cambrian Yanwangbian Formation of southern Shaanxi Province, Central China, has yielded a diverse fossil assemblage that includes abundant bradoriid arthropods, inarticulate brachiopods, hyolithids, trilobites, priapulids, lightly sclerotized arthropods, and ichnofossils. This assemblage represents the biodiversity of Early Cambrian marine communities in South China. Here we describe two new bradoriids from this stratigraphic unit, Sanlangella xixiangensis n. gen. et n. sp. and Kunmingella pentagona n. sp. On the basis of its carapace morphology, S. xixiangensis is assigned to the family Comptalutidae Öpik. The specimens of this species are preserved either in clay minerals or in calcium phosphate. Scanning electron microscopy analysis of phosphatized specimens reveals the microscopic reticulate surface ornaments that form a polygonal pattern on the anterodorsal node, around the base of mid-dorsal spine and along the lateroadmarginal rim. K. pentagona is described as the third species of this preexisting genus, based on the eight specimens with a distinctive pentagonal outline, a prominent anterodorsal curve and an anterodorsal sulcus.     

Occurrence of the earliest known Sphenothallus Hall in the Lower Cambrian of Southern Shaanxi Province, China

Three-dimensionally preserved specimens of an indeterminate species of Sphenothallus Hall occur in limestones in the uppermost Guojiaba and lower Xiannudong formations (Qiongzhusian and early Canglangpuan stages, Lower Cambrian) in southern Shaanxi Province, China. The specimens consist of a small (up to 3 mm long), gradually tapered, subcircular to elliptic (transversely) tube that is broken at both ends, commonly with the fracture edge at the wide (apertural) end of each face forming a V- or U-shaped notch. Some specimens preserve the subconical upper (proximal) part of the holdfast, and all specimens are black. Combined scanning and transmission electron microscopy and energy dispersive elemental analyses show that the tube wall is finely laminated, with individual laminae measuring about 1 μm thick, and consists mainly of calcium phosphate but also contains organic material. Sphenothallus specimens from the Lower Cambrian Guojiaba and Xiannudong formations represent the earliest known record of this genus, and indicate that the origin of this taxon is coeval with and possibly related to the Early Cambrian bioradiation event.     

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。     

Early Cambrian radiolarians and sponge spicules from the Niujiaohe Formation in South China

Most of the reported Cambrian radiolarians are from middle Cambrian (Miaolingian Series, Wuliuan Stage) and onward, the radiolarians from lower Cambrian (Terreneuvian and Cambrian Series 2), on the other hand, are poorly documented, thus their morphological characteristics have not been well understood. In this study, we extracted spherical radiolarians and sponge spicules from the chert of the Cambrian Series 2 Niujiaohe Formation in southern Jiangxi Province, China. The well-preserved radiolarian fossils, identified as Paraantygopora porosa, consist of perforate plate shells pierced by dense pores with elevated rims, and display similarities to those from Lower Ordovician. Seven forms of sponge spicules are recognized, including monaxons, diaxons, tetractines, hexactines, triaxon tetractines, triaxon pentactines and irregular tetraxon tetractines, which are similar to those from the Qiongzhusian Stage in South China. Our results, combined with previously reported early Cambrian radiolarians from South China, indicate that the early Cambrian radiolarians developed advanced spherical skeletons.     

A Middle and Late Cambrian age for the Booley Bay Formation,County Wexford,Ireland: New acritarch data and its implications

A well preserved Ediacara-type fauna was recorded for the first time a few years ago from the bases of seven sandstone beds in the type section of the Lower Palaeozoic Booley Bay Formation in County Wexford, Ireland. Four microfossil samples from mudstones interbedded with the sandstones yielded an acritarch microflora considered indicative of a late Late Cambrian age for the Ediacara fauna, thus suggesting extension of its range from the Neoproterozoic to the Late Cambrian, rather than to the Middle Cambrian as had been previously suggested. The current study examines the microfossils in more detail, with 18 samples, all of which were productive. One additional Ediacara bed approximately 100 m above those recorded earlier was also observed. The exceptionally well preserved acritarch assemblages indicate a clear Middle Cambrian age for the Ediacara beds, thus predating the previously suggested upper limit for Ediacara faunas. The uppermost part of the formation, above known occurrences of Ediacara beds, is younger; that is, early Late Cambrian, probably coeval with the Olenus trilobite zone. In addition, the age now proposed for the Booley Bay Formation shows that it is part of the Lower Palaeozoic Ribband Group of southeast Ireland, and not part of the Cahore Group as has recently been suggested by the Irish Geological Survey. Thirty-seven acritarch species (or species groups) are distinguished and illustrated. One new species, Stellechinatum ? mariatheresae Vanguestaine, is established.     

A new assemblage of dabashanellids (Crustacea: Phosphatocopida) from Cambrian Stage 3 of western Hubei Province,South China

Dabashanellids are univalved phosphatocopid crustaceans, and are among the earliest crustaceans known so far. They were reported mainly from the Cambrian Stage 3 of China, but only a single species was established. Here I report a new assemblage of dabashanellids from the Cambrian Stage 3 Shuijingtuo Formation in western Hubei Province, South China. All specimens are sub-millimetre in length, and are preserved as three-dimensional carbonaceous hollow shields. Five species of Dabashanella were recognized, including the previously reported D. hemicyclica, three new species, D. longa n. sp., D. semiorbiculata n. sp., D. unispinata n. sp., and an indeterminate form Dabashanella sp. In addition, five indeterminate forms of arthropods were recovered. These dabashanellids represent part of a meiofauna that lived in the off-shore, deeper environments of mid-northern Yangtze Sea during Cambrian Age 3. This study shows greater morphological diversity and ecologic disparity of dabashanellid crustaceans, and supports the previous suggestion that the invasion of meiofaunal ecdysozoans into the off-shore, deeper environments probably occurred simultaneously with their radiation in the shallow water.     

Crypto-helical body plan in partially disarticulated gogiids from the Cambrian of South China

All living echinoderms have a pentaradial symmetry that is unique within the Bilateria. However, the Cambrian origin of echinoderm radial/pentaradiate symmetry is a long-standing problem. During the Cambrian (542–488 Ma), gogiids were the most common stalked echinoderm characterized by an “irregularly” plated body. Based on recently discovered material from the Balang Formation (Cambrian Series 2), eastern Guizhou, China, three unusual, partially disarticulated specimens of Guizhoueocrinus have clear evidence for a helical body plan. This helical plating is only evident in partially disarticulated specimens, thus a crypto-helical body construction is present. Crypto-helical construction in a gogiid raises the possibility of a phylogenetic connection among helicoplacoids, gogiids, and Helicocystis. The crypto-helical body construction may be an important evolutionary innovation among pre-radiate echinoderms.     

Skeletal Morphology of Palaeocastor peninsulatus (Rodentia,Castoridae) from the Fort Logan Formation of Montana (early Arikareean): Ontogenetic and Paleoecological Interpretations

Palaeocastorine beavers were diverse members of the burrowing fauna of the Oligocene of North America best known from the Great Plains and the Great Basin. Palaeocastorines are also found in the northern Rocky Mountains. Several specimens of Capacikala, Euhapsis, and Palaeocastor have been reported from Montana within the Cabbage Patch beds fauna. New occurrences of palaeocastorine beavers from the Fort Logan Formation of central Montana show that the fauna there included Palaeocastor fossor, Capacikala sp., Palaeocastor sp., and three specimens of a species previously known only from the John Day Formation of Oregon: Palaeocastor peninsulatus. The three specimens include crania and associated postcrania forming an ontogenetic series from a juvenile to a mature adult. Careful examination of these specimens shows that morphological changes throughout ontogeny are associated with increased burrowing ability in adults. Palaeocastor peninsulatus is a scratch-digger with few cranial adaptations to burrowing susceptible to change with maturity. Dental characters, however, are modified with wear and vary greatly across individuals of similar wear stage. Cranial morphology thus appears to be a reliable source of taxonomic information in palaeocastorines unlike dental material. These new specimens provide evidence for increased chisel-tooth digging in adults compared to juveniles as is observed throughout the evolution of palaeocastorines. This study demonstrates the need for future work focusing on intraspecific variation to help better define species boundaries among palaeocastorines and improve phylogenetic analyses.     

Paterimitra pyramidalis from South Australia: scleritome,shell structure and evolution of a lower Cambrian stem group brachiopod

The tommotiid Paterimitra pyramidalis Laurie, 1986, is redescribed based on well‐preserved material from the lower Cambrian Wilkawillina, Wirrapowie and Ajax limestones of the Flinders Ranges, South Australia. The material shows that the scleritome of Paterimitra pyramidalis includes three sclerite morphotypes (S1, S2 and L). Detailed shell microstructure studies show striking similarities with both the paterinid brachiopod Askepasma toddense and the tommotiid Eccentrotheca helenia, which strengthens the suggested evolutionary link between tommotiids and brachiopods. Based on the partly articulated specimens and similarities in shell microstructure and sclerite morphology with Eccentrotheca, Paterimitra pyramidalis is reconstructed as a tube‐dwelling, epifaunal, sessile, filter‐feeder with an organic pedicle‐like attachment structure. The proposed reconstruction of the scleritome comprises a basal unit composed of one S1 and one S2 sclerite, as well as an unresolved number of L sclerites lining a coniform tubular structure.     

Comparative morphology of the external male genitalia in Lophogastrida, Stygiomysida, and Mysida (Crustacea, Eumalacostraca)

External organs associated with the male gonopore are described for 29 species covering for the first time all seven currently acknowledged, extant families of the orders Lophogastrida, Stygiomysida, and Mysida, and all ten subfamilies of the Mysidae (Mysida). The gonopores are located throughout on the structures of the coxa of the eighth thoracopods. The three orders are consistently differentiated based on their male genital characteristics. Species of the Stygiomysida genera Stygiomysis (Stygiomysidae) and Spelaeomysis (Lepidomysidae) share a closing apparatus formed by two laminar lobes flanking the genital orifice, an anterior setose lobe, and a posterior bare lobe; no tubular penes are developed. In contrast, the Lophogastrida are characterized by a bare, slot-like orifice without lobes; also, in this taxon, no tubular penes are developed. The gonopore is on the inner wall of the coxa without conspicuous elevation in the species of Eucopia (Eucopiidae) and Lophogaster (Lophogastridae) and on the top of an anvil-like elevation in Paralophogaster (Lophogastridae), or of a dome-shaped elevation in Gnathophausia and Neognathophausia (Gnathophausiidae). In all examined species of the Mysida, the gonopores show a closing apparatus formed by lobes; one or more of these lobes is setose in most species. Within the Mysida, the genus Hansenomysis (Petalophthalmidae) and most subfamilies of the Mysidae have well-developed paired penes with (sub) terminal orifice. Only Rhopalophthalmus (Rhopalophthalminae) lacks penes but has bilobate gonopores located without additional elevation at the inner distal corner of the strongly enlarged coxa of the eighth thoracopods; this coxa contains a large seminal vesicle. Within the variety of external male genitalia in the Eumalacostraca, the structures associated with the gonopores appear to be plesiomorphic in Lophogastrida. In the Mysida, they appear to be apomorphic and support the monophyly of this order with respect to the previously published, competing phylogenetic trees. This requires additional evidence in the case of the Stygiomysida.     

Unique lowermost Cambrian small shelly fossils (SSFs) from eastern Yunnan,South China: implications for the early diversification history of animals

With a particular focus on the earliest Cambrian diversification of small shelly fossils (SSFs), stratigraphic analysis was conducted on the lower Cambrian Zhongyicun Member at the Hongjiachong section in the Chengjiang area, Yunnan, China. From ca. 3-m-thick bedded phosphorites (Unit A) in the lower part of the member, we recovered unique SSFs. This interval with 4 SSF-bearing horizons is characterized by the dominance in blade-shaped SSFs, including Halkieria spp., Brushenodus prionodes, Sinosachites delicatus, and Pteronus sp., and the absence of typical tube/cap-shape SSFs common in the Fortunian. This interval tentatively named “Halkieria-dominant interval” is stratigraphically positioned ca. 3 m below the previously known level of the oldest mollusks in the continuous bedded phosphorite sequence between the Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone and the overlying Paragloborilus subglobosa-Purella squamulosa Assemblage Zone of the Fortunian (the earliest Cambrian). The “Halkieria-dominant interval” yields some SSFs likely affiliated with ostracods in view of size and morphology, suggesting that arthropod body fossils appeared in the Fortunian, considerably earlier than previously believed.