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Egg Biology
Objectives:
1. To learn the unique adaptations present in the egg
2. To learn the structure of the egg
3. To learn internal parts of the egg
Materials needed:
1. one uncooked egg
2. bowl
3. pencil
Introduction:
Dinosaurs laid eggs like modern birds and reptiles, and fossil dinosaur eggs have been
found for the past 90 plus years. Oviraptor eggs have been found in China, hadrosaur
eggs have been found in Montana, and sauropod eggs have been found in France. Eggs
have been described as marvels of evolutionary engineering and the purpose of this
laboratory is to introduce you to the wonders of the shelled amniote egg.
Below is a photograph of the surface of a dinosaur egg.
1. How would you describe the surface of a dinosaur egg?
A. It is smooth and shiny.
B. It is furrowed.
C. It is covered with large knobs.
D. It is covered with small bumps
Lets compare the dinosaur egg with a chicken egg. Obtain an uncooked chicken egg.
Take a pencil and mark the egg as if you were doing a pencil rubbing. Describe the
surface of the egg.
2. How would you describe the surface of the chicken egg?
A. It is smooth and shiny.
B. It is furrowed.
C. It is covered with large knobs.
D. It is covered with small bumps
3. How does the chicken egg compare to the dinosaur egg?
A. They are both covered by small bumps.
B. The dinosaur egg is covered by little bumps and the chicken egg is smooth and shiny.
C. Both eggs are smooth and shiny.
D. The chicken egg is covered with large knobs
Not all bird eggs have the same shape and color. Eggs from ledge nesting birds are
narrower at one end than the other so that a rolling egg does not roll off the ledge but
rolls in a circle. Many birds have eggs are a mottled color to help them to blend in with
their surroundings. Below are examples of the varieties of bird eggs.
As the illustration documents there is considerable variation in the size, color and shape
of bird eggs. It should also be noted that not all bird eggs have the same surface features
as a chicken egg. For example, duck eggs are oily and waterproof, Tinamou eggs are
shiny, Cassowary eggs are covered with pits, and cormorant eggs are rough.
Unfortunately, dinosaur egg fossils do not indicate if they were colored or not, but
dinosaur eggs do come in a variety of shapes depending on the type of dinosaur that laid
the eggs. Theropod eggs were long ovals, ceratopsian eggs were more pointed at one end
than the other, and ornithopod eggs were nearly spherical. Below are two photographs of
dinosaur eggs. Based on their shapes, what kind of dinosaurs laid these eggs?
4. The eggs below were laid by a(n)
A. ornithopod
B. theropod
C. ceratopsian
5. The eggs below were laid by a(n)
A. ornithopod
B. theropod
C. ceratopsian
Note that the chicken egg has a blunt end. This end is where an air space is located.
Place the egg in a pan of water that has been brought to a boil and then removed from the
heat.
6. What happens to the egg?
A. It forms bubbles on the surface.
B. It changes color.
C. Nothing happens.
7. What does this mean regarding how solid or porous the eggshell is?
A. the egg is porous.
B. the egg is solid and not porous.
The shelled reptilian egg protects the developing embryo from physical damage and
drying out. It represents a major evolutionary advance over the amphibians, such as frogs
and salamanders, in that it permitted the reptiles to live on land without being tied to
water for reproduction.
Carefully crack open the egg into a bowl without breaking the yolk and examine the
pieces of the shell. The shell is composed of calcium carbonate of which calcium is the
major component. If you have a magnifying glass or hand lens, then you can see that the
shell has three layers. Calcium carbonate is laid down in the egg in crystals that are
arranged at 90-degree angles to the egg surface, which gives the shell its strength.
Examine the internal contents of the egg. The yolk is a single cell surrounded by a thin
cell membrane. The bulk of the yolk is composed of yolk fat spheres floating in a sea of
yolk protein. The yolk is yellow because it contains the same pigments found in carrots.
These pigments, called carotenoids, are used to make vitamin A. The primary function of
the yolk is to nourish the developing embryo.
Examine the clear egg white or albumin. Note that the albumin has regions of different
thickness giving it the appearance of layers. The albumin is mostly water and provides
the embryo with its water needs. Other components of the albumin include proteins that
provide antibacterial and antiviral protection. The different layers of the albumin along
with the white thick string like structures keep the yolk properly oriented with the embryo
facing the top of the egg. When the egg is moved, these strings rotate the yolk.
Look at the yolk in the bowl in relation to the egg white. Does the yolk float or sink? Do
you see a small drop of fluid on the top of the yolk? This is the blastodisc, which
contains the egg nucleus waiting to be fertilized.
8. Does the egg yolk sink or float on the egg white?
A. It floats
B. It sinks
9. What protective action would this (your answer to 8) provide the embryo?
A. By floating, it protects the yolk and developing egg from damage caused by the egg
being moved.
B. By sinking, the yolk would always be on the bottom edge of the egg, and be insulated
from the elements.
C. There is no protective action by either floating or sinking.
Dinosaurs also laid their eggs in patterns that indicates some of them were nest builders.
These nests were often circular such as the nest shown in the photograph below.
These nests are interpreted as evidence that dinosaurs, like birds, exhibited some degree
of parental care.
In the Scientific American readings on sauropods, the authors’ described the egg nests of
sauropods. They laid 20 – 40 eggs per clutch in circular depressions.
10. The sauropods’ eggs were
A. elongated
B. about the size and shape of grapefruits
C. pointed at one end
D. brightly colored