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1. The work of paleontologists begins by searching for the most appropriate place to carry out an excavation. Once the site is chosen, they begin to remove the soil, being very careful not to miss small fossils.

2. With chisels and hammers, the sedimentary rock that surrounds the fossil is removed. Great care must be taken; the bones are usually fractured into many pieces by the effects of geologic processes.

3. Enough rock and soil is removed to leave the bone in the open where it can be cleaned with brushes.

The bones are very heavy. Over millions of years the original material has been replaced by minerals of silica and calcium carbonate.

4. Once the fossil is exposed, it is first covered with wet paper to protect it from the subsequent layer of plaster.

5. The paleontologist covers the bone with fabric covered with wet plaster. When the plaster dries it forms a hard, protective jacket that keeps all the pieces together.

6. With the hard jacket in place, the bottom of the bone is still held by rock. The most difficult moment of the rescue is when separating the fossil bone from the last remaining rock for transport to the laboratory. Sometimes small fragments are lost.

7. Desert Museum collaborators Carlos René Delgado and Nacho Vallejo place the bone in the truck for transport to the Paleontology Laboratory in the museum.

8. In the laboratory, people like Bárbara Oyervides González, biology teacher in Saltillo and volunteer in the Paleontology Laboratory of the Desert Museum, continue cleaning the fossil bone.

9. Assembling the fragments of a single bone requires many hours of work. But assembling a complete skeleton, like these in the Desert Museum, requires many years of labor in the field and laboratory, and is usually accomplished with the bones of more than one animal.