DK Science: In The Field
In the past, dinosaur digs were very different from what they are today. Fragile fossils were broken by crude digging methods, and even more were shaken to pieces on their way to museums. Records were rarely kept of fossil sites. As a result, valuable specimens and information have been lost for ever. Modern excavation involves studying both the skeleton and its surroundings. Like detectives, palaeontologists examine the site for clues about the dinosaur’s life. Then the fossils are carefully removed and prepared for transportation.
When a dinosaur skeleton is discovered, the first thing to do is remove the rock and soil above the layer in which the specimen lies, known as overburden, until only a thin layer is left over the skeleton.
The rock that the fossil is embedded in is called the matrix. This is removed with great care, usually by hand, using fine chisels, brushes, and dental tools. Sometimes the fossilized bones are quite hard and the matrix is loose, crumbly, and easy to clear away. But often the fossil bones and rock have equal hardness, which makes the job more difficult.
The next task is to record exactly where each specimen lies. To do this accurately, a grid of wire or strings is placed over the site to divide it into smaller areas. Everything is photographed, as well as drawn. The mapping covers not only the skeleton, but all the other fossils that lie in the same bed of rock. These might provide useful details about the behaviour of the dinosaur, or how it died.
A map of the site is drawn up showing the position of all the bones. Every piece is catalogued and numbered so it can be identified later when the skeleton is studied in the laboratory. Anything else of interest, such as other fossils or sedimentary structures, is also marked on the map.
Many fossils are very fragile and, before they can be removed and transported, they need to be carefully prepared. First, the fossil is sprayed or painted with a glue or resin that seeps into it and solidifies. This makes the fossil harder. Next it is covered in a protective layer of paper or foil, and wrapped in bandages.
The top of the bone is then covered with runny plaster. When this has set hard, the underside of the fossil can be dug out. It is then turned over and covered in bandages and plaster, so that the whole thing is enclosed in a solid plaster jacket. The fossil is now ready to be packed in a crate and taken to a laboratory.
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