Dissecting Dinosaurs: An exercise in bird anatomy and evolution
What: Students will participate in a dissection of a variety of birds of different species and ages. We will study internal and external anatomy of the birds, and learn about what characteristics they share with other dinosaurs. Students will also participate directly in the scientiﬁc process by collecting data (e.g., molt, stomach contents, reproductive condition) to aid in a doctoral dissertation research project.
Where: This activity will be schedule to take place in on the University of California, Berkeley campus in the Valley Life Sciences Building.
Who: Local East Bay high school students will be led in the exercise by UC Berkeley graduate and undergraduate students.
We provide: Materials to prepare for the activity, specimens and tools for the dissection, safety gear, and follow-up materials for later use in the classroom.
Where do the birds come from? All of the birds for this research project have been donated by wildlife hospitals (such as the Lindsay Wildlife Museum in Walnut Creek). They are all little guys who simply did not make it, or had to be anesthetized.
Safety concerns: None of the birds have passed away from a serious contagious disease, and most have been anesthetized. Additionally, all specimens have been kept frozen for many weeks, which would kill any bacteria. And, of course, all participating students will wear appropriate safety gear; only tweezers and scissors will be used for the dissection (no scalpel blades).
For any questions, please contact: Jessie Atterholt ([email protected]) Dissecting Dinosaurs Outline 1) Major themes a) Birds are living dinosaurs i) How do we know this? (we’ll be looking at several aspects of anatomy that birds share with extinct dinosaurs throughout the dissection) ii) Show cast of Archaeopteryx(?) b) Birds also have most of the same bones as we do, just in different shapes and sizes 2) Molt a) Feathers are one major feature that birds and extinct dinosaurs share i) Show different feather types on samples skin (if available) ii) Distinguish and count primaries & secondaries (1) How many is this taxon supposed to have? Does it have the same # on the right and the left? iii) Examine the tail feathers for molt iv) Mention that we’ll assess body molt later(?) 3) Skull a) Do birds have teeth? b) Identify cere and/or external ear opening? 4) Students cut the bird open from vent to throat, and carefully peel back the skin 5) Throat/neck region a) Identify larynx and crop b) Examine trachea/syrinx (possibly sample syrinx) 6) Wings a) Students cut a slit up the skin of both wings b) Identify the 3 remaining digits i) Notice alula on digit I ii) How does a bird form its wing? Long humerus, very elongate radius+ulna, long digit II—these are all the same bones we have, just with some fused up (in the wrist/hand) and some lost (2 digits) iii) Skin the wings, being very careful not to lose digits I and III 7) Legs a) Students cut a slit up the skin of both legs b) Partially remove one of the legs from the body (disarticulate the femur) to see the perforated acetabulum, another dinosaurian characteristic c) Notice how the feet are the only scaly parts of the bird, indicating their reptilian heritage d) Identify major bones of the leg; how are they the same as what we have? How are they different? i) They also are morphologically very similar to the foot of a theropod dinosaur (show a picture/bring in a cast) e) Skin the legs, ignoring skin on the feet if it’s too hard to get off 8) Students peel the skin off the back and head, removing it completely 9) Flight apparatus a) Compare muscle mass on the chest with that on the back. Which is bigger? Why? b) Examine pectoral muscles, and supracoracoideus (?); identify triosseal foramen, if possible c) Identify furcula; the “wishbone” is another feature birds share with non- avian dinosaurs 10) Viscera a) Identify and remove the liver b) Identify and remove the stomach + intestines i) If possible, examine the differentiated ventriculus and proventriculus ii) Take notes on stomach contents, possibly collect samples iii) Examine length of intestines, identify cecae c) Identify kidneys d) Identify gonads (if possible) e) Find and remove heart f) Collect HLMK tissue sampless Dissecting Your Dinosaur
What kind of bird is it?
Examine the beak. What do you think it is adapted for?
Examine the feet. What do you think they were used for?
Step 1: Identifying Molt
Birds lose their feathers periodically throughout their lives. When a bird loses feathers and is growing new ones, this is called molting.
1. Gently spread the wings of your bird. Do you see any signs of molt (feathers growing it)?
2. Gently spread the tail feathers of your bird. Do you see any signs of molt here?
Secondaries attach to Primaries attach to the ______the ______
Primary flight feathers
Secondary flight feathers
Step 2: Make the First Cut
1. Cutting into the skin: push aside the feathers on the breast and stomach area until you see the skin. Lift the skin on the breast with your fingers or the forceps and cut a hole with your scissors.
2. Cut open up to the throat of the bird and down to the cloaca. IT IS VERY IMPORTANT TO MAKE SURE YOU ARE JUST CUTTING THE SKIN AND NOT THE SKELETON OF THE ABDOMINAL WALL OF THE BIRD. The skin will be a thin, slightly see‐through layer that covers above the muscle on the breast muscle and down the abdomen. When you are cutting, if you encounter anything that is hard or crunchy, STOP, because that’s probably bone. The same is true if you see intestines or “guts.”
3. Don’t hesitate to ask for help if you’re having trouble finding the skin layer.
These are the organs and structures you will see when you first cut open your bird. The heart and lungs will be covered by the large, bony sternum (breast bone). Do not remove the sternum. You will reach into the chest cavity later to remove the heart. Step 3: Identifying the Gonads (testes and ovaries)
1. Opening the abdominal wall: cut open the thin abdominal wall of the bird to expose the intestines and stomach.
2. Gently push the stomach and intestines aside to the left. Look for gonads first on the right (the birds left).
3. Look for the gonads, on top of the kidneys, against the body wall.
4. Testes: male birds will have two testes.
5. Ovaries: most female birds (except for some hawks) have only one ovary, on the left hand side.
6. Gonads vary greatly in size, color, and general appearance. They can be very small, and very tricky to find, so look carefully. You may need to look under a microscope.
7. Ask Zach or Jessie for help if you need it, or to verify that you have found the gonads.
8. Have Zach or Jessie take pictures of the gonads (or area where they should be).
After you’ve removed the internal organs that were on top to take tissue samples and check stomach contents, your bird will look something like this. Now we can clearly see the kidneys, and possibly the gonads (testes or ovaries). Step 4: Collecting Tissue Samples
1. Label a paper towel: lay out a paper towel, and write on it “H L M K” with the letters widely spaced apart. These stand for heart, liver, muscle, kidney, the four tissues you’ll be collecting samples of.
2. Find the pectoral muscle: locate the big flight muscles (breast muscles) on the sternum of the bird. Using your scissors and tweezers, cut a chunk of muscle tissue and place it above the “M” on your labeled paper towel.
3. Find and set aside the stomach and intestines: the guts will be sitting on top of the other viscera, and were probably the most prominent thing when you cut your bird open. Cut open the stomach. Do you see any interesting contents? What are they, or what do they look like?
4. Locate the liver: the liver consists of several large lobes, or pieces, also located prominently on top of everything else, slightly above the stomach. Cut a chunk of liver and place it on your labeled paper towel above “L.” Remove the liver and set it aside.
5. Locate the heart: The heart will be far up in the chest cavity, easily reachable after the liver is removed. Pull it out, cut a chunk of tissue, and place it above the “H” on your labeled paper towel.
6. Find the kidneys: the kidneys are difficult to spot, but they are located against the back of the body wall, near where we looked for gonads. They are much large than the gonads, and will appear elongate and lobed. Once located, cut a tissue sample and place it above “K” on the labeled paper towel.
7. Put the tissue samples in the tissue vial: each group has been given a small tissue vial. Place the tissues inside of this vial in the following order: hear (bottom), liver, muscle, kidney (top). You want samples large enough to fill most of the vial.
Step 5: The Bird Wing
1. While the bird is on its back, pull out one of the wings.
2. Push aside any feathers, and cut a slit up the skin of the wing. Just like when you cut the body open, the skin here is very thin and may be a little difficult to find. It will be the very thin, slightly see‐through layer that you can pinch with tweezers.
3. Gently peel back the skin to expose muscles and bones.
4. Identify the major bones of the bird wing. How does a bird wing differ from the wing of other flying vertebrates (pterosaurs and bats)?
Step 6: The Bird Leg
1. While the bird is on its back, pull out one of the legs.
2. Push aside any feathers, and cut a slit up the skin of the leg. Just like when you cut the body open, the skin here is very thin and may be a little difficult to find. It will be the very thin, slightly see‐through layer that you can pinch with tweezers. However the skin will become very thick and scaly around the foot this will be very difficult to cut through, and don’t struggle with it if it is too hard.
3. Gently peel back the skin to expose muscles and bones.
4. Identify the major bones of the bird leg. How is it similar to the leg of a dinosaur like T. rex? How is it different?