An early Cambrian agglutinated tubular lophophorate with brachiopod characters

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Abstract

The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen. et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagerstätte (Yunnan, China) that exhibits an unusual combination of phoronid, brachiopod and tommotiid (Cambrian problematica) characters, notably a pair of agglutinated valves, enclosing a horseshoe-shaped lophophore, supported by a lower bipartite tubular attachment structure with a long pedicle with coelomic space. The terminal bulb of the pedicle provided anchorage in soft sediment. The discovery has important implications for the early evolution of lophotrochozoans, suggesting rooting of brachiopods into the sessile lophotrochozoans and the origination of their bivalved bauplan preceding the biomineralization of shell valves in crown brachiopods.

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A critical reappraisal of the fossil record of the bilaterian phyla.

Jakob S Jensen, S Jensen (2000)

It has long been assumed that the extant bilaterian phyla generally have their origin in the Cambrian explosion, when they appear in an essentially modern form. Both these assumptions are questionable. A strict application of stem- and crown-group concepts to phyla shows that although the branching points of many clades may have occurred in the Early Cambrian or before, the appearance of the modern body plans was in most cases later: very few bilaterian phyla sensu stricto have demonstrable representatives in the earliest Cambrian. Given that the early branching points of major clades is an inevitable result of the geometry of clade diversification, the alleged phenomenon of phyla appearing early and remaining morphologically static is seen not to require particular explanation. Confusion in the definition of a phylum has thus led to attempts to explain (especially from a developmental perspective) a feature that is partly inevitable, partly illusory. We critically discuss models for Proterozoic diversification based on small body size, limited developmental capacity and poor preservation and cryptic habits, and show that the prospect of lineage diversification occurring early in the Proterozoic can be seen to be unlikely on grounds of both parsimony and functional morphology. Indeed, the combination of the body and trace fossil record demonstrates a progressive diversification through the end of the Proterozoic well into the Cambrian and beyond, a picture consistent with body plans being assembled during this time. Body-plan characters are likely to have been acquired monophyletically in the history of the bilaterians, and a model explaining the diversity in just one of them, the coelom, is presented. This analysis points to the requirement for a careful application of systematic methodology before explanations are sought for alleged patterns of constraint and flexibility.

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Halwaxiids and the early evolution of the lophotrochozoans.

Simon Morris, Jean-Bernard Caron (2007)

Halkieriids and wiwaxiids are cosmopolitan sclerite-bearing metazoans from the Lower and Middle Cambrian. Although they have similar scleritomes, their phylogenetic position is contested. A new scleritomous fossil from the Burgess Shale has the prominent anterior shell of the halkieriids but also bears wiwaxiid-like sclerites. This new fossil defines the monophyletic halwaxiids and indicates that they have a key place in early lophotrochozoan history.

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Phylogenetic relationships within the lophophorate lineages (Ectoprocta, Brachiopoda and Phoronida).

Bernhard Hausdorf, Martin Helmkampf, Maximilian P Nesnidal … (2010)

We produced two new EST datasets of so far uncovered clades of ectoprocts to investigate the phylogenetic relationships within the lophophorate lineages, Ectoprocta, Brachiopoda and Phoronida. Maximum-likelihood analyses based on 78 ribosomal proteins of 62 metazoan taxa support the monophyly of Ectoprocta and a sister group relationship of Phylactolaemata living in freshwater and the mainly marine Gymnolaemata. Hypotheses suggesting that Ectoprocta is diphyletic with phylactolaemates forming a clade with phoronids or paraphyletic with respect to Entoprocta could be rejected by topology tests. The hypotheses that Stenolaemata are the sister group of all other ectoprocts, that Stenolaemata constitutes a monophyletic group with Cheilostomata, and that Phylactolaemata have been derived from Ctenostomata could also be excluded. However, the hypothesis that Phylactolaemata and Stenolaemata form a monophyletic group could not be rejected. Brachiopoda and Phoronida constitute a monophylum, Brachiozoa. The hypotheses that phoronids are the sister group of articulate or inarticulate brachiopods could be rejected by topology tests, thus confirming the monophyly of Brachiopoda. 2009 Elsevier Inc. All rights reserved.

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Author and article information

Journal

Journal ID (nlm-ta): Sci Rep

Journal ID (iso-abbrev): Sci Rep

Title: Scientific Reports

Publisher: Nature Publishing Group

ISSN (Electronic): 2045-2322

Publication date (Electronic): 15 May 2014

Publication date Collection: 2014

Volume: 4

Electronic Location Identifier: 4682

Affiliations

[1 ]Early Life Institute, State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University , Xi'an, 710069, China

[2 ]LPS, Nanjing Institute of Geology and Palaeontology , Chinese Academy of Sciences, Nanjing, 210008, China

[3 ]Uppsala University, Department of Earth Sciences , Palaeobiology, Villavägen 16, SE-752 36 Uppsala, Sweden

[4 ]Department of Biological Sciences, Macquarie University , Sydney, New South Wales 2109, Australia

[5 ]University of Glasgow, Department of Geographical and Earth Sciences , Gregory Building, Lilybank Gardens, G12 8QQ, Glasgow, United Kingdom

[6 ]Department of Palaeobiology, Swedish Museum of Natural History , Box 50007, SE-104 05 Stockholm, Sweden

Author notes

[a ] elizf@ 123456nwu.edu.cn ; zhangelle@ 123456126.com

Article

Publisher Item ID: srep04682

DOI: 10.1038/srep04682

PMC ID: 4021322

PubMed ID: 24828016

SO-VID: 822df865-a57a-4f1c-9553-1b9ef9da3b80

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An early Cambrian agglutinated tubular lophophorate with brachiopod characters

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Abstract

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Most cited references 6

A critical reappraisal of the fossil record of the bilaterian phyla.

Halwaxiids and the early evolution of the lophotrochozoans.

Phylogenetic relationships within the lophophorate lineages (Ectoprocta, Brachiopoda and Phoronida).

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