Reconsideration of the supposed naraoiid larva from the Early Cambrian Chengjiang Lagerstätte, South China

The Chengjiang Lagerstätte in the Lower Cambrian of South China yields a small, larva‐like arthropod, which was considered to be a protaspis of naraoiids by many authors. The discovery of a large number of well‐preserved specimens from many new localities has allowed the original study to be revised. The relatively large size, stable morphology and unusual structure of the appendages indicate that these specimens represent adults of a new arthropod, Primicaris larvaformis. The larva‐like outline is considered to have arisen by the heterochronic process of progenesis. In addition, this animal displays primitive aspects of bodyplan and limb morphology that suggest a basal position within arachnomorphs, or perhaps even arthropods, and the similarities to the Vendian arthropod‐like animal Parvancorina probably provide an evolutionary link between Vendian forms and Cambrian arthropods.     

Morphology of Cambrian lobopodian eyes from the Chengjiang Lagerstätte and their evolutionary significance

Visual organs are widely distributed throughout the animal kingdom and exhibit a great diversity of morphologies. Compound eyes consisting of numerous visual units (ommatidia) are the oldest preserved visual systems of arthropods, but their origins are obscure and hypothetical models for their evolution have been difficult to test in the absence of unequivocal fossil evidence. Here we reveal the detailed eye structures of well-preserved Early Cambrian lobopodians Luolishania longicruris and Hallucigenia fortis from the Chengjiang Lagerstätte, China. These animals possess a pair of eyes composed of at least two visual units, interpreted as pigment cups. Contrary to previous suggestions that Cambrian lobopodians possessed ocellus-like eyes comparable to those of extant onychophorans, this multi-component structure is more similar to the lateral eyes of arthropods. Morphological comparison and phylogenetic analyses indicate that these lobopodian eyes may represent an early stage in the evolution of the ancestral visual system of euarthropods.     

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.     

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.     

The exceptionally preserved Early Cambrian stem rhynchonelliform brachiopod Longtancunella and its implications

Zhang, Z., Holmer, L. E., Ou, Q., Han, J. & Shu, D. 2011: The exceptionally preserved Early Cambrian stem rhynchonelliform brachiopod Longtancunella and its implications. Lethaia, Vol. 44, pp. 490–495. The extraordinary Longtancunella chengjiangensis is one of the rarest and most problematic brachiopods from the Early Cambrian Chengjiang Lagerstätte, where it occurs in unique gregarious clusters with up to ten individuals attached by their stout pedicles to a single hard exoskeleton. Although the general morphology and soft anatomy of Longtancunella is available, its taxonomy and systematic placement within the Brachiopoda remains problematic. New exceptionally preserved specimens show that the pedicle of Longtancunella cannot be considered homologous with the pedicles in crown Rhynchonelliformea or Linguliformea. The pedicle of Longtancunella emerges from a ventral umbonal foramen with a rounded plate that must have been secreted by specialized ventral mantle epithelium. The rounded plate is proposed to be a homologue to the colleplax – a plate covering the umbonal foramen, which is otherwise known from the extinct rhynchonelliform chileates. Longtancunella is proposed to represent a soft‐shelled stem rhynchonelliform brachiopod with chileate features, thus demonstrating for the first time that the chileate‐like umbonal perforation functions as a pedicle opening. The unusual preservation of the annulated chileate‐like holdfast supports the view that it may have been secreted as stacks of chitinous or even mineralized ‘attachment pads’. Together with having a spirolophous lophophore and U‐shaped gut, Longtancunella displays a unique mixture of linguliform and rhynchonelliform characters that throw new light on an early stage of rhynchonelliform diversification. □Brachiopods, Cambrian, Chengjiang Lagerstätte, Chileata, colleplax, pedicle.     

A new red alga preserved with possible reproductive bodies from the 518-million-year-old Qingjiang biota

Macroalgae have been a key ecological component of marine ecosystems since the Proterozoic period and are common fossil forms in Cambrian Burgess Shale-type Lagerstätten. However, in most cases, it is difficult to place these early fossil algae into modern groups because little distinctive morphology is preserved. Here, we describe a new form of macroalgae, Qingjiangthallus cystocarpium gen. & sp. nov., from the Qingjiang biota of South China. The new taxon is represented by 546 specimens remarkably preserved with characteristics that allow a phylogenetic placement into crown groups of red algae. Centimeter-sized thalli resemble members of the extant Rhodymeniophycidae (a subclass of the class Florideophyceae), and hence suggest a florideophycean affinity, which indicates that ahnfeltiophycidaen and rhodymeniophycidaen algae may have diverged at least 518 Ma, accordant with estimations of molecular studies. The presence of possible cystocarps on Qingjiangthallus thalli suggests that evolutionary innovation of a triphasic life cycle in red algae may have occurred no later than the Early Cambrian. The branching patterns and branch width of Qingjiangthallus are consistent with the coarsely dichotomously branched morphogroup, which was previously present in the Ediacaran, Ordovician, and afterward, but absent in the Cambrian.     

DEVELOPMENT AND DIVERSIFICATION OF TRUNK PLATES OF THE LOWER CAMBRIAN LOBOPODIANS

Abstract:  Isolated lobopodian plates are reported from Early Cambrian strata at five localities in southern China. A wide variety of morphologies is represented, reflecting a considerable diversification within the phylum at this time. The new taxon Microdictyon jinshaense is erected and new observations are recorded on established taxa, based on examination of more than 600 well-preserved plates; irregular patterns of node distribution and the presence of large spines are documented on some taxa for the first time. Rare specimens in which two plates are conjoined, with a larger plate underlying a smaller one, are interpreted as showing a new sclerite emerging underneath its predecessor, which has not yet been moulted. These specimens confirm the process of ecdysis in the lobopodians and contribute to a fuller understanding of the ontogeny of these organisms. A functional hypothesis that suggests that the plates were complex visual structures is refuted; it is possible that they were sites of muscle attachment, but a protective role is regarded as more plausible.     

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.     

A palaeoscolecid worm from the Burgess Shale

Palaeoscolecid worms are a ubiquitous group of Early Palaeozoic ecdysozoans that are curiously lacking in the archetypal Cambrian Lagerstätten, the Burgess Shale. Here I describe Scathascolex minor gen. et sp. nov, the first unequivocal palaeoscolecid from this site. Scathascolex is armoured with simple Hadimopanella‐like plates, but lacks smaller platelets, pointing to a close affinity with the Palaeoscolecida sensu stricto. Neither preservational nor environmental factors account for the scarcity of palaeoscolecids in the Burgess Shale, which presumably represents an ecological phenomenon.     

The morphology and affinity of anabaritids revealed by their internal molds from the Cambrian Fortunian,southern Shaanxi,China

Anabaritids are a group of tubular skeletal fossils known from the lower Cambrian worldwide. Many previously collected specimens of anabaritids lack both the apical and apertural regions, and thus their complete morphology and growth patterns are not fully understood. Here we describe a number of internal molds of Anabarites from the lower Cambrian (Fortunian Stage) Zhangjiagou Lagerstätte, southern Shaanxi Province. Our new specimens preserved the apex, the aperture with three lobes, and three longitudinal grooves initiating apically rather than adapically as previously reported. This work enriches the morphology of anabaritids, casting doubt on the previous proposition that anabaritids originated from a cylindrical tubular ancestor. It is proposed here that a triradial symmetry may have been established in very early ontogenetic stages of some anabaritids; furthermore, the aperture with three lobes resembles those of olivooids and thus supports a possible close relationship between anabaritids and olivooid scyphozoans.     

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.     

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.     

Early Cambrian lobopodian sclerites and associated fossils from Kazakhstan

A low diversity fossil assemblage dominated by Mongolitubulus spines, from the Early Cambrian Geres Member of the Shabakhty Formation at Koksu, Malyi Karatau, Kazakhstan, enables identification of its sclerite variability within the scleritome. No other sclerotised structures could be matched with the spines, indicating that these were the only sclerotised part of the body and were periodically shed. The prominent spines of Mongolitubulus have a scale–like external ornamentation and fibrous internal structure. Possibly they armed the body of a lobopodian similar to Xenusion . The Mongolitubulus spines belong to a series of Cambrian phosphatic fossils, the other end members of which are sclerites of Microdictyon , the second most abundant component of the Koksu assemblage. The latter superficially resemble schizochroal trilobite eyes, but in life covered the dorso–lateral sides of the body segments, as is evident from complete specimens from the Chinese Chengjiang locality. A pair of sclerites of Microdictyon , representing uncompleted exuviation, from Koksu show that each hole originally contained a non–phosphatised lenticular body. This makes a compound eye nature of the Microdictyon sclerites likely, and even their homology with arthropod eyes cannot be excluded.     

A new xandarellid arthropod from the Chengjiang Lagerstätte,Lower Cambrian of Southwest China

A new arthropod, Luohuilinella rarus nov. gen., nov. sp., is described from the Lower Cambrian Chengjiang Lagerstätte (Series 2, Stage 3), Yunnan, Southwest China. Luohuilinella nov. gen. is extremely rare in this Lagerstätte, represented by a single specimen. It has a large cephalic shield and a tapering trunk with well-developed pleural field. The cephalic shield is crescentic in outline and its anterolateral margin has two notches. The trunk is weakly trilobate, composed of 27 distinct tergites with well-developed pleural spines and a terminal piece. Luohuilinella nov. gen. resembles xandarellids in overall body architecture and especially in the reduced first trunk tergite. Its ventral morphology is, however, presently unknown. Therefore, it is provisionally assigned to Xandarellida.     

A cryptic record of Burgess Shale‐type diversity from the early Cambrian of Baltica

Exceptionally preserved ‘Burgess Shale‐type’ fossil assemblages from the Cambrian of Laurentia, South China and Australia record a diverse array of non‐biomineralizing organisms. During this time, the palaeocontinent Baltica was geographically isolated from these regions, and is conspicuously lacking in terms of comparable accessible early Cambrian Lagerstätten. Here we report a diverse assemblage of small carbonaceous fossils (SCFs) from the early Cambrian (Stage 4) File Haidar Formation of southeast Sweden and surrounding areas of the Baltoscandian Basin, including exceptionally preserved remains of Burgess Shale‐type metazoans and other organisms. Recovered SCFs include taxonomically resolvable ecdysozoan elements (priapulid and palaeoscolecid worms), lophotrochozoan elements (annelid chaetae and wiwaxiid sclerites), as well as ‘protoconodonts’, denticulate feeding structures, and a background of filamentous and spheroidal microbes. The annelids, wiwaxiids and priapulids are the first recorded from the Cambrian of Baltica. The File Haidar SCF assemblage is broadly comparable to those recovered from Cambrian basins in Laurentia and South China, though differences at lower taxonomic levels point to possible environmental or palaeogeographical controls on taxon ranges. These data reveal a fundamentally expanded picture of early Cambrian diversity on Baltica, and provide key insights into high‐latitude Cambrian faunas and patterns of SCF preservation. We establish three new taxa based on large populations of distinctive SCFs: Baltiscalida njorda gen. et sp. nov. (a priapulid), Baltichaeta jormunganda gen. et sp. nov. (an annelid) and Baltinema rana gen. et sp. nov. (a filamentous problematicum).     

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.     

First record of the brachiopod Lingulella waptaensis with pedicle from the Middle Cambrian Burgess Shale

Pettersson Stolk, S., Holmer, L. E. and Caron, J ‐B. 2010. First record of the brachiopod Lingulella waptaensis with pedicle from the Middle Cambrian Burgess Shale. —Acta Zoologica (Stockholm) 91 : 150–162 The organophosphatic shells of linguloid brachiopods are a common component of normal Cambrian–Ordovician shelly assemblages. Preservation of linguloid soft‐part anatomy, however, is extremely rare, and restricted to a few species in Lower Cambrian Konservat Lagerstätten. Such remarkable occurrences provide unique insights into the biology and ecology of early linguloids that are not available from the study of shells alone. Based on its shells, Lingulella waptaensis Walcott, was originally described in 1924 from the Middle Cambrian Burgess Shale but despite the widespread occurrence of soft‐part preservation associated with fossils from the same levels, no preserved soft parts have been reported. Lingulella waptaensis is restudied herein based on 396 specimens collected by Royal Ontario Museum field parties from the Greater Phyllopod Bed (Walcott Quarry Shale Member, British Columbia). The new specimens, including three with exceptional preservation of the pedicle, were collected in situ in discrete obrution beds. Census counts show that L. waptaensis is rare but recurrent in the Greater Phyllopod Bed, suggesting that this species might have been generalist. The wrinkled pedicle protruded posteriorly between the valves, was composed of a central coelomic space, and was slender and flexible enough to be tightly folded, suggesting a thin chitinous cuticle and underlying muscular layers. The nearly circular shell and the long, slender and highly flexible pedicle suggest that L. waptaensis lived epifaunally, probably attached to the substrate. Vertical cross‐sections of the shells show that L. waptaensis possessed a virgose secondary layer, which has previously only been known from Devonian to Recent members of the Family Lingulidae.     

Morphology of Luolishania longicruris (Lower Cambrian,Chengjiang Lagerstätte,SW China) and the phylogenetic relationships within lobopodians

New material of the lobopodian Luolishania longicruris has been recovered from the Lower Cambrian Chengjiang Lagerstätte, southwest China. The specimens throw new light on several morphological features of the species, including the paired antenniform outgrowths, eyes, head shield, setae and other cuticular projections, as well as the differentiated sclerites, appendages, claws, and lobopod interspaces. L. longicruris shows well developed tagmosis: a distinct head and a trunk divided into two sections. The new data allow a revised comparison with other lobopodians. Miraluolishania haikouensis Liu et al., 2004 is considered to be a junior synonym of L. longicruris Hou and Chen, 1989. Evidence from gut filling and specialized morphological characters indicates that L. longicruris may have had a filter feeding lifestyle. A new cladistic analysis suggests that fossil lobopodians are paraphyletic or even polyphyletic and L. longicruris may be an important representative of the stem lineage leading to arthropods.     

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.     

Biological controls upon the physical taphonomy of exceptionally preserved salamanders from the Miocene of Rubielos de Mora,northeast Spain

McNamara, M.E., Orr, P.J., Manzocchi, T., Alcalá, L., Anadón, P. & Peñalver, E. 2011: Biological controls upon the physical taphonomy of exceptionally preserved salamanders from the Miocene of Rubielos de Mora, northeast Spain. Lethaia, Vol. 45, pp. 210–226. The middle Miocene Rubielos de Mora Konservat‐Lagerstätte of northeast Spain is hosted within profundal, finely laminated, lacustrine mudstones. The diverse biota includes abundant salamanders. Most individuals died during separate episodes and sank rapidly postmortem. Specimens are typically preserved in dorso‐ventral aspect, the most hydrodynamically stable orientation. The near‐cylindrical morphology of the body, however, allowed some carcasses to settle in or subsequently re‐orientate into, lateral orientations. Loss of skeletal elements (i.e. reduced completeness) reflects their location within the body and followed a distal to proximal trend. Two stages are identified: initial loss of a small number of phalanges, followed by loss of more proximal limb bones plus additional phalanges. Disarticulation is more complex: it occurred via several mechanisms (notably, abdominal rupture and re‐orientation of part of the body and limbs during decay) and shows no consistent pattern among specimens. The physical taphonomy of the salamanders is controlled predominantly by intrinsic biological factors, i.e. the geometry of the body and of individual skeletal elements, the orientation, inherent strength and location of specific joints and the extent to which soft tissues, particularly the skin, persist during decay. These biological factors probably control patterns of physical taphonomy of other fossil tetrapods with a similar skeletal configuration. □Articulation, completeness, Konservat‐Lagerstätten, orientation, quantitative taphonomy, salamanders.