2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 226-9
Presentation Time: 10:30 AM-10:45 AM


MOORE, John L., Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106, jlmoore@umail.ucsb.edu, LI, Guoxiang, State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing, 210008, China, and PORTER, Susannah M., Earth Science, University of California at Santa Barbara, Santa Barbara, CA 93106

Chancelloriids are a group of enigmatic metazoans known from Cambrian rocks around the world. Specimens from Burgess Shale-type deposits show that chancelloriids were sessile, radially symmetric animals covered with sclerites in the form of rosettes of spines, producing an appearance like that of a barrel cactus. The phylogenetic position of chancelloriids remains controversial, due in part to the lack of knowledge of their soft anatomy, with some authors suggesting that they are sponge-like animals or early-branching eumetazoans with plesiomorphic radial symmetry, while others interpret them as being secondarily simplified due to the similarities in sclerite structure between chancelloriids and halkieriids, presumed mollusc-like spiralians. Isolated sclerites of chancelloriids are widespread in small shelly faunas from Cambrian carbonates, but they have proven difficult to treat taxonomically due to the variation within and between individuals and the common use of taxonomic concepts based on only one or a few specimens. We report here the results of a study of large populations of chancelloriid sclerites from two sections from the Meishucunian (pre-trilobitic Lower Cambrian) of eastern Yunnan Province, China: Zhujiaqing, Dahai, Huize County (with material from the Dahai Member, Zhujiaqing Formation) and Xiaotan, Yongshan County (with material from the Shiyantou Formation). The Dahai section contains many sclerites similar to those traditionally placed in the genus Chancelloria, while the Xiaotan section is characterized by sclerites that could be placed in the genera Archiasterella and Allonnia. Despite the considerable variation in sclerite morphology, it is possible to recognize several distinct morphotypes. Statistical analysis of morphotype cooccurrences in different samples shows that they have different distributions, suggesting they may represent different taxa. This conclusion confirms previous limited reports of chancelloriids from Burgess Shale-type deposits with relatively minor variability in sclerite morphology. Our study supports the idea that careful study of large collections of isolated chancelloriid sclerites permits the identification of different species, opening the possibility of their use for evolutionary or stratigraphic studies.

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 226
Paleontology IV: Morphology and Phylogeny
Minneapolis Convention Center: Room 205CD
8:00 AM-12:00 PM, Wednesday, 12 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 545

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