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A Production of

Polysacos vickersianumFossil, Fossil Chiton
Dr. Michael J. Vendrasco - University of California, Los Angeles
Troy E. Wood, Bruce N. Runnegar
Polysacos vickersianum
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skull
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National Museum of Natural History (USNM uncatalogued)

Image processing: Dr. Matthew Colbert
Image processing: Ms. Rachel Racicot
Publication Date: 03 Sep 2004

ITIS TNS Google MSN

Abstract from Vendrasco et al. (2004):

Articulated Palaeozoic fossil with 17 plates greatly expands disparity of early chitons

Modern chitons (Mollusca: Polyplacophora) possess a highly conserved skeleton of eight shell plates (valves) surrounded by spicules or scales, and fossil evidence suggests that the chiton skeleton has changed little since the first appearance of the class in the Late Cambrian period (about 500 million years before present, Myr BP). However, the Palaeozoic problematic taxon Multiplacophora, in spite of having a more complex skeleton, shares several derived characters with chitons. The enigmatic status of the Multiplacophora is due in part to the fact that its members had an exoskeleton of numerous calcium carbonate valves that usually separated after death. A new articulated specimen from the Carboniferous period (about 335 Myr BP) of Indiana reveals that multiplacophorans had a dorsal protective surface composed of head and tail valves, left and right columns of overlapping valves (five on each side), and a central zone of five smaller valves, all surrounded by an annulus of large spines. Here we describe and name the articulated specimen and present evidence that multiplacophorans were chitons. Thus the highly conserved body plan of living chitons belies the broad disparity of this clade during the Palaeozoic era.

About the Species

This specimen was collected from the the Crawford Shale (Carboniferous in age) near Bloomington, Indiana. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Troy Wood of the Department of Biology, Indiana University and Dr. Michael Vendrasco of the Department of Earth and Space Sciences, The University of California at Los Angeles. Funding for scanning was provided by a National Science Foundation IGERT grant to Dr. Wood.

About this Specimen

The specimen was scanned by Matthew Colbert on 21 April 2003 along the coronal axis for a total of 540 1024x1024 pixel slices. Each slice is 0.057 mm thick, with an interslice spacing of 0.057 mm. and a field of reconstruction of 43 mm.

About the
Scan

Literature

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Conway Morris, S., and J. S. Peel. 1995. Articulated halkieriids from the Lower Cambrian of North Greenland and their role in early protostome evolution. Philosophical Transactions of the Royal Society of London, B, 347:305–358.

Dzik, J. 1986. pp. 116-134 in A. Hoffman and M. H. Nitecki (eds.), Problematic Fossil Taxa. Oxford Univ. Press, New York.

Eernisse, D. J., and P. D. Reynolds. 1994. pp. 55-110 in F. W. Harris, and A. J. Kohn (eds.), Microscopic Anatomy of Invertebrates, Vol. 5, Mollusca I. Wiley Liss, New York.

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Kniprath, E. 1980. Ontogenetic plate and plate field development in two chitons, Middendorffia and Ischnochiton. Rouxs Archives of Developmental Biology 189:97–106.

Pojeta, J. Jr., D. J. Eernisse, R. D. Hoare, and M. D. Henderson. 2003. Echitonichiton dufoei: a new spiny Ordovician chiton. Journal of Paleontology 77:646–654.

Runnegar, B., J. Pojeta, M. E. Taylor, and D. Collins. 1979. New species of the Cambrian and Ordovician chitons Matthevia and Chelodes from Wisconsin and Queensland: evidence for the early history of polyplacophoran mollusks. Journal of Paleontology 53:1374–1394.

Scheltema, A. H., and D. L. Ivanov. 2002. An aplacophoran postlarva with iterated dorsal groups of spicules and skeletal similarities to Paleozoic fossils. Invertebrate Biology 121:1–10.

Sutton, M. D., Briggs, D. E. G., David J. Siveter, and Derek J. Siveter. 2001. An exceptionally preserved vermiform mollusc from the Silurian of England. Nature 410:461–463.

Sutton, M. D., D. E. G. Briggs, David J. Siveter, and Derek J. Siveter. in press. Computer reconstruction and analysis of the vermiform mollusc Acaenoplax hayae from the Herefordshire Lagerstätte (Silurian, England), and implications for molluscan phylogeny. Palaeontology.

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Van Name, W. G. 1925. The supposed Paleozoic barnacle Protobalanus and its bearing on the origin and phylogeny of the barnacles. American Museum Novitates 197:1–8.

Van Name, W. G. 1926. A new specimen of Protobalanus, supposed Paleozoic barnacle. American Museum Novitates 227:1–6.

Vendrasco, M. J., T. E. Wood, and B. N. Runnegar. 2004. Articulated Palaeozoic fossil with 17 plates greatly expands disparity of early chitons. Nature 429:288-291.

Williams, A., and L. E. Holmer. 2002. Shell structure and inferred growth functions and affinities of the sclerites of the problematic Micrina. Palaeontology 45:845–873.

Withers, T. H. 1915. Some Palaeozoic fossils referred to the Cirripedia. Geological Magazine 6:112–123.

Literature
& Links

Click on the thumbnail below to see an animation of the fossil chiton spinning as the matrix fades (1mb):

Front page image:

Additional
Imagery

To cite this page: Dr. Michael J. Vendrasco, Troy E. Wood, Bruce N. Runnegar, 2004, "Polysacos vickersianum" (On-line), Digital Morphology. Accessed November 26, 2014 at http://digimorph.org/specimens/Polysacos_vickersianum/.

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