University of Kansas, Lawrence, KS 66045
This is a single face of
showing the curved membranes which made up the algae. Ca. 75mm on a
The same cube was CT (CAT) scanned with a
Electric 9800 Advantage. The scans were 1.5 mm thick and taken each 1.5
mm. The .tif CT image files were copied onto 3.5 inch floppies and
into an IBM compatible microcomputer with 64 mb of RAM and 4 mb of RAM
on the video card. The CPU was a 233MHz AMD K6. The files were
with JASC's Paint Shop Pro to an 8 bit uncompressed format that could
read by Fortner Software's 3-D imaging program, T3D, known formerly as
This figure shows a
scale CT scan slice about midway through the rock. The light colored
and swirls are the algal fossil membranes. Note the black hole toward
middle of the rock. X1.5
T3D reads the numerical sequence of 46 image files to build a data volume saved in .hdf format of about 3.2 mb in size. The volumes were then modified so that only the algal membranes were visible. Interesting views were saved as .svw files about 12.4 kb in size.
A typical view shows how very numerous the algae
in the rock but also raises questions about their form. It is apparent
that the algae were commonly fused together suggesting budding as a
of asexual reproduction. Apparent sexual
reproduction in a different species of Ivanovia from
the Yukon has been noted.
A view of the deep
interior of the
specimen that shows the detail revealed by the CT scans. A detailed
of many such views shows that these are branches of dichotomously
utricles. Ca. 250 X
A view of utricular casts, as seen below,
cavities that are presumed vacuoles.
A highly magnified view of
of the utricular casts showing at right center a dichotomous pair of
casts. Ca. 500 X
animation is of 19 (out of 92) Z-axis, high resolution CT sections of
being stacked one at a time to illustrate and to study utricular
The frame with the most white background is frame number 1. Ca.
Although this work has now been published (J. Paleontology, 73:154-158, 1999), it has raised many questions about earlier concepts of the form of the alga. Indeed, features can be studied that would have been obscured by traditional serial sectioning or other destructive methods. The project also demonstrates that CT scanning can be used as a powerful, but nondestructive method for studying fossils and that the data can be processed on readily available desktop computers with reasonably priced software.
The next step in this project was to explore the possibility of making a 3-dimensional model or replica of the algal thallus using rapid prototyping or stereolithography, a process that reconstructs the thallus from the CT slices. A report on that effort is just a click away.
Thanks to Don Toomey who collected the rock in Tunisia, to Linda Lucas who helped with the initial medical CT scans, to Richard A. Ketcham who took the high resolution scans at the University of Texas-Austin, and to Cathrin DeNooyer who helped with the computer imaging.
For a brief CV of the author, click here.
This page was last updated on 27 Oct 06.
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