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.
[Illustration: 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.
After all of the bones are cleaned and cemented together the vertebral
column is laid out in its proper sequence on a sand table. Special care
is exercised to be sure that the vertebrae fit correctly with each
other. In this way the correct curvature of the vertebral column is
determined. The proper relationships of the hip bones and ribs to the
vertebrae, the shoulder blade to the ribs, and elements of the limb
bones to each other are determined in the same manner. All of this work
is necessary to correctly fashion the steel framework which will support
the skeleton when it is placed on exhibition. The results of this
careful work must be the framework of an animal which could, if living,
easily go through the normal activities of life such as securing food
and escaping enemies.
Now that the framework of an animal has been set up so that it could
move about if it had muscles, skin, and life, how do we know how large
the muscles were and where they were placed? It is necessary to have a
thorough knowledge of the muscles of a recent animal similar to the one
we are restoring so that we will know what we are looking for in the
fossil. The areas at which muscles are attached to bones are called
muscle scars and are identified by their rough surfaces. Often the
necessary information can be obtained from publications which usually
represent the work done by graduate students for advanced degrees. At
other times we must make our own investigation. Thus if we know what
muscle we are looking for and the size and shape of its muscle scar, we
can determine whether the muscle is a spindle-shaped mass or a broad
sheet.
After we have determined the size and position of the muscles which
operate the limbs, head, and neck, we have a reasonably accurate idea of
the external form of the animal, but we still know nothing of the nature
of the skin which covered the body. Since dinosaurs were reptiles, we
are obliged to assume that they were covered with a scaly skin in order
to preserve the body moisture. None of the modern reptiles possess sweat
glands in the skin. If they did not possess a waterproof covering of
scales they would die in a few hours as a result of the loss of body
moisture by evaporation through the skin. It is possible that some of
the marsh dwellers like _Apatosaurus_ had naked skin which was, as in
the elephant, nearly an inch thick. The elephant does not possess sweat
glands but the outer half of its skin is composed entirely of dead cells
which form a covering as waterproof as the scales of today’s reptiles.
There have been only a few lucky finds of mummified dinosaurs which show
the impressions of the scales. We know that all lizards do not possess
the same type of scales, and therefore, by analogy, we cannot assume
that the dinosaurs did. Eventually, we will probably find that the
dinosaurs exhibited as great a variety of scale-types as do today’s
lizards. As yet we have found nothing in the fossil record which
indicates the color of the dinosaurs. Again, we can only assume that
they exhibited as great a variety of colors as do our lizards. So also,
we assume their body functions were somewhat similar to the reptiles and
other related animals we know today.
[Illustration: DINOSAUR FOSSIL WITH SKIN AND LIGAMENTS PRESERVED.
(NOT FROM DINOSAUR QUARRY. COURTESY, AMERICAN MUSEUM OF NATURAL
HISTORY.)]
[Illustration: RARE FOSSIL OF DINOSAUR SKIN. (COURTESY, AMERICAN
MUSEUM OF NATURAL HISTORY.)]