| 1 - Start By Cleaning
the Bones |
Fossil
technicians in Paul Sereno’s
Working Dinosaur Lab at the University
of Chicago use a variety of tools,
including brushes, dental tools, tweezers,
eye droppers, pin vices, tiny air-powered
jack hammers and even microscopes
to clean rock away from fossil bones |
 |
| 2
- Study and Repair the Original Fossils |
From
left to right: Rajasaurus tailbone, backbone, neckbone, braincase,
and the tools used to clean and repair
them. |
 |
| Once
the matrix has been taken off, the fossil
is taken upstairs to the “Clean
Room.” The “Clean Room”
is where broken bones are reconstructed,
usually with clay. |
| 3
- Make a Mold |
Tyler
Keillor, a technician in Dr. Sereno’s
lab, puts silicone rubber over the braincase
as he prepares a new mold.
|
|
How
are molds made?
After a fossil is cleaned and repaired,
a mold can be made. A kind of “moat”
is built up with clay around the edges
of the fossil to be cast. Molds are
made by layering silicone rubber and cheesecloth,
then fiberglass directly on the cleaned
fossil.
Once one side is done, the fossil
is turned over and the process is
repeated. The two sides are screwed
together and plastic is poured inside
to make an exact replica of the original
fossil. |
| 4
- And Then Make a Cast |
 |
 |
| The mold is complete
and now copies (“casts”)
can be made and a skull can be reconstructed. |
First plastic (epoxy)
copy, or cast, of the braincase. |
Why
make casts of fossils? Why not just
use the real bones?
The number one reason is to protect the original bones - fossils are heavy and fragile. Casts
are lighter and easier to move around
and because they are exact replicas,
casts can be used for scientific study
and to build life-sized dinosaurs (or
crocodiles!). |
| 5
- Use the Casts to Build a Complete
Skull |
|
 |
| The cast bones are assembled
into a skull model. Green plasticene
clay is used to bridge the gaps and
to sculpt missing bones. |
A mold is made of the
complete skull model so that a replica
of the complete skull can be made. |
| Fossil reconstructions,
like the skull of Rajasaurus, are complicated
and often require three- or multi-part
molds. |
| 6
- Paint the Casts to Match the Original
Fossils |
The
final plastic cast of the skull –
composed of the cranium and two mandibles,
is painted to closely resemble the
original fossil material. Tyler is
painting the mandible (lower jaw)
of the cast presented to the National
Museum of Natural History in Mumbai
during the scientific announcement
on August 13, 2003. |
|
| See
more photos of Dr. Sereno's Lab |
