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Cited by 52Paleontology and Evolutionary BiologyPaleontology and Stratigraphy of FossilsEvolution and Paleontology Studies

SKELETAL MICROSTRUCTURE INDICATES CHANCELLORIIDS AND HALKIERIIDS ARE CLOSELY RELATED

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PORTER, SUSANNAH M.·2008·Palaeontology
DOI 10.1111/j.1475-4983.2008.00792.x
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Abstract

Abstract: Chancelloriids are problematic, sac‐like animals whose sclerites are common in Cambrian fossil assemblages. They look like sponges, but were united with the slug‐like halkieriids in the group Coeloscleritophora Bengtson and Missarzhevsky, 1981 based on a unique mode of sclerite construction. Because their body plans are so different, this proposal has never been well accepted, but detailed study of their sclerite microstructure presented here provides additional support for this grouping. Both taxa possess walls composed of a thin, probably organic, sheet overlying a single layer of aragonite fibres orientated parallel to the long axis of the sclerite. In all halkieriids and in the chancelloriid genus ArchiasterellaSdzuy, 1969, bundles of these fibres form inclined projections on the upper surface of the sclerite giving it a scaly appearance. On the lower surface of the sclerite, the projections are absent. This microstructure appears to be unique to chancelloriids, halkieriids, and their relatives, siphogonuchitids and sachitids. (The sclerites of another putative halkieriid relative, WiwaxiaWalcott, 1911, are unmineralized, making direct comparisons impossible.) Thus, similarity both at the level of sclerite construction and the level of sclerite microstructure suggests that chancelloriid, halkieriid, sachitid, and siphogonuchitid sclerites are homologous. The difference in chancelloriid and halkieriid body plans can be resolved in two ways. Chancelloriids either represent a derived condition exhibiting complete loss of bilaterian characters or they represent the ancestral condition from which the bilaterally symmetric halkieriids, and the Bilateria as a whole, derived. The latter interpretation, proposed by Bengtson (2005), implies that coeloscleritophoran sclerites (‘coelosclerites’) are a plesiomorphy of the Bilateria, lost or transformed in descendent lineages. Given that mineralized coelosclerites appear in the fossil record no earlier than c. 542 Ma, this in turn implies either that the Ediacaran record of bilaterians has been misinterpreted or that coelosclerite preservability increased at the beginning of the Cambrian Period. The former is difficult to reconcile with Ediacaran trace and body fossil evidence, but the latter may be possible, reflecting either independent mineralization of organic‐walled sclerites in chancelloriids and halkieriids or the opening of a taphonomic window that favours coelosclerite preservation.

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  • Representatives of the Halwaxiida have been united with sedentary Chancelloriida in the problematic Coeloscleritophora, whose members share possession of hollow calcareous sclerites secreted at a fixed size by internal soft tissue and a similar skeletal microstructure.

    “Representatives of the Halwaxiida have been united with sedentary Chancelloriida in the problematic Coeloscleritophora, whose members share possession of hollow calcareous sclerites secreted at a fixed size by internal soft tissue and a similar skeletal microstructure”

    From Chronology of early Cambrian biomineralization (2012) · cites this paper as Porter, 2008

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  • Halwaxiids can be considered to be stem-group lophotrochozoans, while the general body morphology and affinity of chancelloriids is more problematic.

    “Halwaxiids can be considered to be stem-group lophotrochozoans, while the general body morphology and affinity of chancelloriids is more problematic”

    From Chronology of early Cambrian biomineralization (2012) · cites this paper as Porter, 2008

    The introductory passage describes halkieriid features as suggesting a relationship with lophotrochozoans, and the Abstract and Discussion describe chancelloriid body plans and affinities as problematic. The paper does not establish halwaxiids as stem-group lophotrochozoans: its Wiwaxiid sclerites section says the relationship of wiwaxiids to the other animals discussed is disputed. (LLM, conf=0.86)

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Research works printed but not linked: 4

  1. In B R I G G S , D. E. G. (ed.). Evolving form and function: fossils and develop- ment. Special Publication of the Peabody Museum of Natural History, Yale University, New Haven, CT, 288 pp.
  2. L O W E N S T A M , H. A. 1989. Spicular morphology and miner- alogy in some Pyuridae (Ascidiacea). Bulletin of Marine Science, 45, 243-252.
  3. In Z H U R A V L E V A , I. (ed.). Biostratigraphy and palaeontology of the Lower Cambrian of Siberia and the Far East. Nauka, Moscow, 227 pp.
  4. --2004b. Halkieriids in Middle Cambrian phosphatic lime- stones from Australia. Journal of Paleontology, 78, 574-590.

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Authors
PORTER, S. M.
Affiliations
University of California, Santa Barbara (US)
Corresponding author
PORTER, SUSANNAH M.
ORCID
PORTER, SUSANNAH M.
Venue
Palaeontology
Publisher
Wiley
Published
2008-07
Volume
51
Issue
4
Pages
865-879
ISSN
  • 0031-0239 (ISSN-L)
  • 1475-4983
DOI
10.1111/j.1475-4983.2008.00792.x
OpenAlex
W2148235125
Cited by
52
References
63
Citations by year
2026: 2 · 2025: 4 · 2024: 4 · 2023: 2 · 2022: 2 · 2021: 3 · 2020: 1 · 2019: 7 · 2018: 4 · 2017: 4 · 2015: 4 · 2014: 5 · 2013: 2 · 2012: 2
FWCI
1.52
Type
journal article
Language
en
Open access
Licence
onlinelibrary.wiley.com/termsAndConditions#vor (vor, 14 d)
Locations
Palaeontology (publishedVersion)
Funders
  • National Aeronautics and Space Administration
  • NASA Astrobiology Institute
Topics
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Evolutionary Biology
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
Keywords
chancelloriids, Ediacaran biota, homology, Cambrian fossils, Cambrian explosion

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