New and interesting dinosaurs were present among the flesh-eaters. Horned forms, somewhat similar to the rhinoceros but much larger, were common. Also common were the turtle-like ankylosaurs. Perhaps the oddest and most interesting dinosaurs of the Cretaceous were the two-footed hadrosaurs. These excellent swimmers had weird head shapes with complicated skull passages and openings. They were a very successful group and at least 15 different kinds are known from the Cretaceous rocks of North America.
WHAT THEY LOOKED LIKE
Ideas about the external appearances of dinosaurs have been developed after many years of work and study. They are a combination of the ideas of several people who had studied different specimens of a single species. Let us review briefly the materials and work necessary to arrive at a reasonably accurate picture of the body form and external appearance of these strange reptiles.
The first requirement for arriving at a good idea of the build and physical attitude of an animal is a nearly entire skeleton. We cannot have too much of the animal’s skeleton missing or we may make a serious error. But if the left hind leg is missing and we have the right, we are not seriously handicapped. However, if both hind legs are missing we must restore them according to a similar animal whose hind legs are known.
After the nearly entire skeleton has been found it must be collected with great care. This is a rather involved process and, for some of the large dinosaurs, 2 or 3 months work may be required. The specimen is first uncovered and the fossil bone is treated with a preservative such as gum arabic, shellac, or one of the plastics. An accurate diagram of the specimen as it lies in the rock is made on cross-ruled paper. A trench 2 or 3 feet wide is then dug around the specimen. The depth of the trench is determined by the width of the specimen and the nature of the rock.
PUTTING PLASTER CAST ON A FOSSIL BEFORE REMOVING IT FROM THE QUARRY.
If the specimen is too large to take out in one piece, as most dinosaurs are, it is divided into sections which are numbered serially as they are taken out. Each section is bandaged in strips of burlap dipped in plaster of Paris. After the plaster has set, the section is turned over and the bottom is sealed with burlap and plaster. The section is labeled with the appropriate number and the section and number are shown on the diagram.
When all of the sections have been bandaged and numbered they are packed in strong wooden boxes and shipped to the laboratory.
The work in the laboratory is more involved than that in the field, and extreme care must be exercised to be sure that the bones will be undamaged. In most cases the bones have been broken by natural causes as they lay in the rock before discovery. All the pieces of each bone must be thoroughly cleaned and securely cemented together. This is a very time-consuming task and for a large dinosaur like Apatosaurus it requires 3 men 4 or 5 years to complete the task.