Lower Cambrian Vendobionts from China and Early Diploblast Evolution

Department of Earth Sciences, University of Cambridge, Cambridge, England, United Kingdom
Science (Impact Factor: 33.61). 06/2006; 312(5774):731-4. DOI: 10.1126/science.1124565
Source: PubMed


Ediacaran assemblages immediately predate the Cambrian explosion of metazoans and should have played a crucial role in this radiation. Their wider relationships, however, have remained refractory and difficult to integrate with early metazoan phylogeny. Here, we describe a frondlike fossil, Stromatoveris (S. psygmoglena sp. nov.), from the Lower Cambrian Chengjiang Lagerstätte (Yunnan, China) that is strikingly similar to Ediacaran vendobionts. The exquisite preservation reveals closely spaced branches, probably ciliated, that appear to represent precursors of the diagnostic comb rows of ctenophores. Therefore, this finding has important implications for the early evolution of this phylum and related diploblasts, some of which independently evolved a frondose habit.

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    • "These latter and better biostratigraphically constrained isotope data are consistent with a continuous diversification of Early Cambrian biota across these shifts, and in many sections the latest Ediacaran elements co-occur with the earliest representants of early Cambrian fauna (e.g., Cloudina with anabaritids on the Siberian Platform; Cloudina with probable Platysolenites on the West Siberian Plate, Kontorovich et al. 2008; vendotaeniids with complex trace fossils in Spain, Vidal et al. 1994; vendobionts with trace fossils of Phanerozoic aspect in Namibia, Jensen and Runnegar 2005).Judging from radiometric dating, Grazhdankin (2004) suggested that a whole typical Ediacaran soft-bodied community (Tribrachidium, Dickinsonia) had still survived about 541±4 Ma in Ukraine (Mogilev Formation). Although claims for a discovery of Cambrian 'Ediacaran' fossils are not uncommon (Conway Morris 1993; Crimes et al. 1995; Jensen et al. 1998; Hagadorn et al. 2000; Lin et al. 2006; Shu et al. 2006), none of them, even frondlike Stromatoveris described by Shu et al. (2006) from the Chengjiang Lagerstätte of China, possesses features typical of Ediacaran vendobionts whose peculiar organisation is supported by uniquely preserved specimens and by a growth pattern analysis (Zhuravlev 1993; Grazhdankin 2004; Narbonne 2004; Xiao et al. 2005; Ivantsov and Naimark 2007; Antcliffe and Brasier 2008). "
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    ABSTRACT: New finds of skeletal fossils in the terminal Neoproterozoic of the Siberian Platform and Spain. Acta Palaeolntologica Polonica 57 (1): 205-224. doi:10.4202/app.2010.0074 A current paradigm accepts the presence in the terminal Neoproterozoic (Ediacaran) of weakly biomineralized animals only, barely above a low metazoan grade of organization, and a later, early Cambrian burst of well skeletonized animals. Here we report new assemblages of primarily calcareous shelly fossils from upper Ediacaran (553−542 Ma) carbonates of Spain and Russia (Siberian Platform). The problematic organism Cloudina is found in the Yudoma Group of the southeastern Siberian Platform and different skeletal taxa have been discovered in the terminal Neoproterozoic of several provinces of Spain. New data on the morphology and microstructure of Ediacaran skeletal fossils Cloudina and Namacalathus indicate that the Neoproterozoic skeletal organisms were already reasonably advanced. In total, at least 15 skeletal metazoan genera are recorded worldwide within this interval. This number is comparable with that known for the basal early Cambrian. These data reveal the terminal Neoproterozoic skeletal bloom was a real precursor of the Cambrian radiation. Cloudina, the oldest animal with a mineralised skeleton on the Siberian Platform, characterises the uppermost Ediacaran strata of the Ust'-Yudoma Formation. While in Siberia Cloudina co-occurs with small skeletal fossils of Cambrian aspect, in Spain Cloudina-bearing carbonates and other Ediacaran skeletal fossils alternate with strata containing rich trace-fossil assemblages. These finds treated together provide a possibility to correlate transitional Neoproterozoic–lower Cambrian strata around the world. Such a correlation concurs with available isotope and radiometric data and indicates that typical Ediacaran shelly fossils have not crossed the Precambrian-Cambrian boundary.
    Full-text · Article · Mar 2012 · Acta Palaeontologica Polonica
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    • "A similar conclusion is reached with the enigmatic attached leaf-shaped animal Thaumaptilon [25] from the Burgess Shale. This animal may have affinities with some frondose Ediacaran forms [25] or represent a potential stem group cnidarian [26], but affinities to S. gregarium seem very remote. Priscansermarinus [27], another problematic stalked Burgess Shale animal originally thought to be a barnacle, is most likely unrelated to this group [28]. "
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    ABSTRACT: Burgess Shale-type deposits provide invaluable insights into the early evolution of body plans and the ecological structure of Cambrian communities, but a number of species, continue to defy phylogenetic interpretations. Here we extend this list to include a new soft-bodied animal, Siphusauctum gregarium n. gen. and n. sp., from the Tulip Beds (Campsite Cliff Shale Member, Burgess Shale Formation) of Mount Stephen (Yoho National Park, British Columbia). With 1,133 specimens collected, S. gregarium is clearly the most abundant animal from this locality. This stalked animal (reaching at least 20 cm in length), has a large ovoid calyx connected to a narrow bilayered stem and a small flattened or bulb-like holdfast. The calyx is enclosed by a flexible sheath with six small openings at the base, and a central terminal anus near the top encircled by indistinct openings. A prominent organ, represented by six radially symmetrical segments with comb-like elements, surrounds an internal body cavity with a large stomach, conical median gut and straight intestine. Siphusauctum gregarium was probably an active filter-feeder, with water passing through the calyx openings, capturing food particles with its comb-like elements. It often occurs in large assemblages on single bedding planes suggesting a gregarious lifestyle, with the animal living in high tier clusters. These were probably buried en masse more or less in-situ by rapid mud flow events. Siphusauctum gregarium resembles Dinomischus, another Cambrian enigmatic stalked animal. Principal points of comparison include a long stem with a calyx containing a visceral mass and bract-like elements, and a similar lifestyle albeit occupying different tiering levels. The presence in both animals of a digestive tract with a potential stomach and anus suggest a grade of organization within bilaterians, but relationships with extant phyla are not straightforward. Thus, the broader affinities of S. gregarium remain largely unconstrained.
    Preview · Article · Jan 2012 · PLoS ONE
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    • "Observation on our new materials attributed to X. sinica has identified a holdfast and feather-like tentacles that have many long branches extending alternately from the tentacle axis. These features suggest that Xianguangia might be an Ediacaran survivor, a case similar to Stromatoveris [45], and thus its affinity to soft-bodied sea anemones [44] is difficult to accept. Archisaccophyllia from the Lower Cambrian Chengjiang biota is a possible Cambrian actiniarian anemone with 12 tentacles and longitudinal bands on the body column but no preserved mesenteries [26]. "
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    ABSTRACT: Abundant fossils from the Ediacaran and Cambrian showing cnidarian grade grossly suggest that cnidarian diversification occurred earlier than that of other eumetazoans. However, fossils of possible soft-bodied polyps are scanty and modern corals are dated back only to the Middle Triassic, although molecular phylogenetic results support the idea that anthozoans represent the first major branch of the Cnidaria. Because of difficulties in taxonomic assignments owing to imperfect preservation of fossil cnidarian candidates, little is known about forms ancestral to those of living groups. We have analyzed the soft-bodied polypoid microfossils Eolympia pediculata gen. et sp. nov. from the lowest Cambrian Kuanchuanpu Formation in southern China by scanning electron microscopy and computer-aided microtomography after isolating fossils from sedimentary rocks by acetic acid maceration. The fossils, about a half mm in body size, are preserved with 18 mesenteries including directives bilaterally arranged, 18 tentacles and a stalk-like pedicle. The pedicle suggests a sexual life cycle, while asexual reproduction by transverse fission also is inferred by circumferential grooves on the body column. The features found in the present fossils fall within the morphological spectrum of modern Hexacorallia excluding Ceriantharia, and thus Eolympia pediculata could be a stem member for this group. The fossils also demonstrate that basic features characterizing modern hexacorallians such as bilateral symmetry and the reproductive system have deep roots in the Early Cambrian.
    Full-text · Article · Oct 2010 · PLoS ONE
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