- A
- B
- C
Listen to a lecture in a biology class, take detailed notes while listening.
controversial – causing lots of disagreement
hollow – to be empty inside; not solid
scale – stiff plate covering reptiles instead of skin
skeletal – relating to the skeleton or the bone structure of an organism
tissue – material formed from plant or animal cells
Fill in the following diagram.
Theory
1.
Support
A 2.
B 3.
C 4.
Now answer the questions using your notes.
Origin of Birds
Which evidence does the professor mention to support the theory that birds are descendants of dinosaurs? Place a check mark in the correct box.
Summarize the text using your notes and diagram.
- 1: Birds are direct descendants of coelurosaurian dinosaurs.
- 2: Both have hollow bones.
- 3: Both have feathers and scales.
- 4: Both have similar skeletal structures.
Listen again:
W1: Today, we'll talk about the origin of birds. This is a discussion of one popular, but controversial theory. And, uh, that theory states that birds are direct descendants from dinosaurs, specifically one group of bird-like dinosaurs called coelurosaurian dinosaurs. If this theory is correct, then birds are living relatives of dinosaurs.
M: Wait, you're saying birds, like pigeons, are related to dinosaurs?
W1: That is correct.
W2: Seems strange to me too.
W1: Okay, then let's take a closer look at the evidence. Then you can make up your mind. Now, have you ever broken open a chicken bone? What does it look like?
M: It's hollow inside.
W1: That's correct. Um, so, bird bones are hollow. Well, actually, they are filled with air sacs–but the point is they are unlike mammal bones, which are solid. Because bird bones are hollow, this helps reduce their weight, which, you know, is important for flight. Well, remember that group of dinosaurs, coelurosaurian dinosaurs? Take a guess what their bones were like.
W2: Hollow?
W1: Exactly–um, place them side by side W1th a bird bone, and they would look very similar. Now, how can you tell birds apart from other animals?
W2: That's easy–they fly. Well most of them do, anyway.
W1: Okay. How do they fly?
M: They have wings and, uh, feathers.
W1: Feathers–good. You might be surprised to know that recently discovered fossils provide evidence that some coelurosaurian dinosaurs also had feathers, or coverings that looked very similar to feathers. When you usually think of dinosaurs, you don't think of feathers. You think of scales. But the interesting thing is, scales grow from tissues that are similar to those that produce feathers. Also, remember, birds sort of do have types of scales ... on their feet! The third thing is, there are dozens of structural skeletal features that are very similar between modern birds and coelurosaurian dinosaurs. To name a few: long curved necks, wrists, shoulder blades, and many others. The point here is that if you compare the features of bird and coelurosaurian dinosaur skeletons, you find many structural similarities and features that set them apart from reptiles, land-based descendants of dinosaurs.
