Hostname: page-component-78c5997874-fbnjt Total loading time: 0 Render date: 2024-11-03T01:05:23.969Z Has data issue: false hasContentIssue false
  • English
  • Français

Digital reconstruction of calcified early metazoans, terminal Proterozoic Nama Group, Namibia

Published online by Cambridge University Press:  08 February 2016

Wesley A. Watters  and
John P. Grotzinger
Wesley A. Watters
Affiliation:
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. E-mail: [email protected]
John P. Grotzinger
Affiliation:
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

A method is presented for the digital reconstruction of weakly calcified fossils within the Nama Group, Namibia. These recently described fossils (Grotzinger et al. 2000) are preserved as calcitic void-fill in a calcite matrix, and individual specimens cannot be freed by conventional techniques. The technique presented here has several integrated steps: (1) the analysis of cross-sections of fossil specimens, (2) the construction of a three-dimensional “tomographic” model that is assembled from the cross-sections, (3) the development of an idealized mathematical model based upon geometric parameters measured from the tomographic model, and (4) the visualization of randomly oriented cross-sections through the mathematical model, which can be compared with fossil cross-sections in outcrop.

In this procedure, rocks containing the fossils are ground and digitally photographed at thickness intervals of 25 μm. A battery of image-processing techniques is used to obtain the contour outlines of the fossils in serial cross-sections. A Delaunay triangulation method is then used to reconstruct the morphology from tetrahedrons which connect the contours in adjacent layers. We found that most of the fossils represent a single morphology with some well-defined characters that vary slightly among individual specimens. This fossil morphology was described by Grotzinger et al. (2000) as Namacalathus hermanastes. A mathematical description of the morphology is used to obtain a database of randomly oriented synthetic cross-sections. This database reproduces the vast majority of cross-sections observed in outcrop.

Type
Articles
Information
Paleobiology , Volume 27 , Issue 1 , Winter 2001 , pp. 159 - 171
Copyright
Copyright © The Paleontological Society 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Literature Cited

Benson, R. H., Chapman, R. E., and Siegel, A. F. 1982. On the measurement of morphology and its change. Paleobiology 8:328–339.CrossRefGoogle Scholar
Chapman, R. E. 1989. Computer assembly of serial sections. Pp. 157–164in Feldmann, et al. 1989.Google Scholar
Fabbri, A. G. 1984. Image processing of geological data. Van Nostrand Reinhold, New York.Google Scholar
Feldmann, R. M., Chapman, R. E., and Hannibal, J. T. 1989. Paleotechniques. Paleontological Society Special Publication 4. Department of Geological Sciences, University of Tennessee, Knoxville.Google Scholar
Foote, M. 1989. Perimeter-based Fourier analysis: a new morphometric method applied to the trilobite cranidium. Journal of Paleontology 63:880–885.CrossRefGoogle Scholar
Gonzales, R. C. 1993. Digital image processing. Addison-Wesley, Reading, Mass.Google Scholar
Grant, R. E. 1989. Extraction of fossils from carbonates by acid. Pp. 237–243in Feldmann, et al. 1989.Google Scholar
Grotzinger, J. P., Watters, W. A., and Knoll, A. H. 2000. Calcified metazoans in thrombolite-stromatolite reefs of the terminal Proterozoic Nama Group, Namibia. Paleobiology 26:334–359.2.0.CO;2>CrossRefGoogle Scholar
Hofmann, H. J. 1990. Computer simulation of trace fossils with random patterns, and the use of goniograms. Ichnos 1:15–22.CrossRefGoogle Scholar
Hofmann, H. J. 1976. Stromatoid morphometrics. Pp. 45–54in Walter, M., ed. Stromatolites. Elsevier, Amsterdam.CrossRefGoogle Scholar
Palmer, A. R. 1989. Techniques for mechanical preparation of smaller fossils. Pp. 208–212in Feldmann, et al. 1989.Google Scholar
Sandy, M. R. 1989. Preparation of serial sections. Pp. 146–156in Feldmann, et al. 1989.Google Scholar
Schmidtling, R. C. II. 1995. Three-dimensional reconstruction of the hydrospires of Pentremites rusticus (Echinodermata: Blastoidea). . University of California, Los Angeles.Google Scholar
Seilacher, A. 1989. Vendozoa: organismic constructions in the Proterozoic biosphere. Lethaia 22:229–239.CrossRefGoogle Scholar
Thompson, D'A. W. 1942. On growth and form, new ed. Reprint, 1963. Cambridge University Press, Cambridge.Google Scholar
Watters, W. A. 2000. Digital reconstructions of fossil morphologies, Nama Group, Namibia. . Massachusetts Institute of Technology, Cambridge.Google Scholar