CT SCANS OF STS 14 PROVIDE THE POTENTIAL FOR MANUFACTURING CASTS
Sts 14 is a partial skeleton of
Australopithecus africanus, discovered in 1947 at Sterkfontein by Broom
and Robinson.[1,2] It represents the South African counterpart to
'Lucy', a partial skeleton of Australopithecus afarensis. Although
casts have been made of the pelvic bones and sacrum of Sts 14, the
fragility of most of the vertebrae has prevented the manufacture of
moulds of the vertebral column. Here we report the results of a
feasibility study, using an industrial X-ray computed tomography (CT)
scanner to manufacture a cast of one vertebra (Sts 14e), which could be
used as one of many master positives for the mass production of casts
of Sts 14.
CT images of Sts 14e were generated using an
Actis+ industrial tomography system (Bio-Imaging Research Inc.,
Lincolnshire, Illinois), and a Philips 320 kV X-ray tube with a 0.8-mm
focal spot size. A linear array solid state detector was used, having
2048 detectors in a 50-mm length and an entrance slit approximately 0.2
mm wide, enabling high resolution images to be obtained. For the
examination of Sts 14, the source was operated at 250 kV, 2 mA, with a
1.8-mm copper filter in the beam. Images were taken at 0.5-mm intervals
with a slice thickness of 0.2 mm. Figures 1 and 2 show two images which
were used as part of the three-dimensional reconstruction of Sts 14e.
The use of dilute acetic acid during preparation has led to the partial
dissolution of lime in the centre of the vertebra. The fragility of
this vertebra is most noticeable in areas where calcite has been
dissolved. The master positive was produced using a Stratsys fused
deposition modeller (Fig. 3).
The production of casts of other elements of
Sts 14 (or indeed of other fragile and valuable fossils) by means of CT
scanning clearly is an advantage over conventional moulding techniques,
which require direct contact with the fossils. Readers interested in
obtaining such casts should contact J.F.T.
This work is supported by the CSIR, the Foundation for Research Development and the Transvaal Museum.
PHOTO (BLACK & WHITE): Fig. 1. (Left) CT
scan of Sts 14e, a vertebra of Australopithecus africanus, discovered
in 1947 by Robert Broom and John Robinson at Sterkfontein. Imaging with
a slice thickness of 0.2 mm has revealed detail of trabecular bone with
unprecedented high resolution. Fig. 2. (Right) Another CT scan of Sts
14e.
PHOTO (BLACK & WHITE): Fig. 3. The
original and cast of Sts 14c. The cast (on the right) was obtained by
means of high resolution CT scanning. Scale in centimetres.
- Broom R. and Robinson J.T. (1950). Notes on the pelves of fossil ape-man. Am. J. phys. Anthrop. 8, 489.
- Robinson J.T. (1972). Early Hominid Posture and Locomotion. University of Chicago Press, Chicago.
~~~~~~~~ By Anthony N. Kirkbride, Simon C. Yates and J. Francis Thackeray
Anthony N. Kirkbride and Simon C. Yates
are in the Division of Materials Science and Technology, CSIR, P.O. Box
395, Pretoria, 0001 South Africa; J.F. Thackeray is in the Department
of Palaeontology and Palaeoenvironmental Studies, Transvaal Museum,
P.O. Box 413, Pretoria, 0001 (e-mail: mrsples@global.co.za).
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