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CAT svans

>      As I have heard it, there are two main reasons for thinking
>_Nanotyrannus_ is a juvenile.  The first is that CAT scans are not always
>terribly reliable when used on fossils.  They work well on materials of
>much different density, but in the case of fossils, the fossil bone and
>the matrix are so close to the same density that the CAT scanner has
>trouble telling them apart.  This is why so many CAT scans of dinosaur
>eggs end in failure, not neccesarily because the eggs do not contain
>embryos, but because the CAT scanner has too much difficulty telling bone
>from matrix.

We have been mucking arounf CAT scanning various fossils, including
dinosaur eggs, crocodile skulls and Messel fish and the difference in
density is the least of our worries. The problem is not picking up the
difference in densities between fossil and matrix, on the contrary, these
are usually more than adequate, but the real problem is that the matrix and
fossil is so dence that the CAT scans have problems penetrating any block
much larger than a shoe box. Add to this the problem of most CAT scanners
only have a hole big enough to accommodate a human in cross section and you
realise that the biggest specimen you can accommodate with standard
equipment is not particularly large (particularly for dinosaur specimens).

Cheers, Paul

Dr Paul M.A. Willis
Consulting Vertebrate Palaeontologist
Quinkana Pty Ltd