Biology: The Dynamics of Life, North Carolina Edition
THE ORIGINS OF BIRDS
Have you ever really looked at a bird’s feet? Most birds have clawed toes and scales covering their feet. Birds also lay eggs in nests. These three traits are found in reptiles as well. However, birds have many other traits, such as feathers and warm-bloodedness,
that are not found in modern reptiles. One of the most famous fossils ever found is Archaeopteryx, a small animal with clawed toes, scaly legs, teeth, and feathered wings. Archaeopteryx was found in rocks dating from the Jurassic Period, 150 million years ago. Many scientists classify Archaeopteryx as a bird. Other scientists point out that, if you took away the feathers, this fossil would look just like Deinonychus, a small theropod dinosaur. Scientists agree that Archaeopteryx wasn’t able to fly, partly because it had a flat sternum (breastbone). Birds have a keeled sternum to which flight muscles are attached. Yet Archaeopteryx clearly had feathers. Was this fossil a dinosaur or a bird? This is only one of the many questions paleontologists struggle with when they study the evolution of birds.
One of the first people to make a connection between dinosaurs and birds was Thomas Huxley, a contemporary of Charles Darwin in the 1800s. In 1916, a Danish doctor named Heilmann wrote a book titled The Origin of Birds, in which he listed the similarities between the skeletons of theropod dinosaurs and modern birds. Later fossil discoveries made these similarities more striking. In the 1960s, an American named John Ostrom found 22 features in theropods and birds that could not be found in any other animal groups. However, new fossils of birds and birdlike dinosaurs are being discovered every year. Some of these fossils are changing perceptions of the origins of birds. Did birds evolve from theropods or another group of dinosaurs? Or did birds and dinosaurs evolve from a common ancestor much earlier in geologic time? Is Archaeopteryx the first bird? When did feathers evolve and how? Which came first, feathers or flight? These are some of the questions you will explore in this WebQuest.
Your job in this WebQuest is to form an opinion as to the origins of birds. You will have to find out what evidence supports the theory that birds descended from theropod dinosaurs. You will have to identify the similarities among birds and other groups of animals. You will also learn about new fossils that provide additional information about the evolution of birds. You will prepare a table in which you compare and contrast several fossils that may, or may not, be links in the evolutionary history of birds. Finally, you will use the information from your Internet research and the table you have prepared to answer the following question: are birds really dinosaurs?
Look at the web sites given here to find the information that will enable you to make an informed decision about the origin of birds.
- Archaeopteryx: An Early Bird.Visit this site to learn about fossils of Archaeopteryx, a 150-million-year-old fossil from Germany. You can find out why fossils of Archaeopteryx provide strong phylogenetic links between birds and reptiles.
- Aves: Fossil Record.Visit this site by the Museum of Paleontology, University of California, Berkeley to learn about the fossil record of birds. At this site you can find out about a new bird fossil found in China and how it compares to Archaeopteryx, a fossil of nearly the same age.
- It’s a Bird, It’s a …Dinosaur?Go to this Scientific American magazine online site to read an article about fossil birds. The article discusses evidence for, and against, the theory that birds are dinosaurs.
- Are Birds Really Dinosaurs?At this DinoBuzz site you can learn about the evidence that supports the theory that birds are theropod dinosaurs. You can read about why most scientists accept the idea that birds and dinosaurs are related, based on phylogeny and cladistics.
- Dinosaurs and Birds: The Story.Visit this excellent site for an interesting description of systematics, the science of evolutionary relationships. This site discusses how scientists identify evolutionary relationships among groups of organisms such as dinosaurs and birds. The site includes a good history of thoughts on bird evolution, and some evidence that shows that birds are not descended from dinosaurs.
- Evidence Supports Dinosaur-Bird Evolution.At this site you can learn about another piece of evidence that links birds to dinosaurs. Tiny vessels in bones called canaliculi form patterns in bones. Only modern birds and coelurosaur dinosaurs share circuitous patterns of canaliculi.
- New Questions About Bird Evolution.Go to this site to read about the newest find that challenges thoughts about the evolution of birds. The fossil is called Longisquama. It is an archosaur, a member of a reptile group that gave rise to dinosaurs, crocodiles, and birds.
- Feathers, scutes, and the origin of birds.Visit this site to read an interesting article about the relationships among dinosaurs and birds. The author discusses new findings that show how scutes, a type of scale seen in crocodiles and on bird feet, can develop into feathers.
2 class periods; a total of 60 minutes for Internet research, 20 minutes to prepare table and answer question
Now that you have completed your research on the Internet, prepare a table that lists the bird and/or birdlike dinosaur fossils that provide some evidence of the origins of birds. In the left column, write the genus names of the fossils you have studied. At the top of the rows, write in the age of the fossil, where it was found, and why it is important to the study of bird evolution. The table is started for you below.
Table 1. Origins of Birds
Name of Fossil
(millions of years)
|was an archosaur, a type of reptile; was neither a bird nor a dinosaur; had complex set of feathers and a furcula (wishbone) - both bird characteristics
|has clawed toes, scaly feet, wings, feathers (bird characteristics); has teeth, flat sternum (reptile characteristics)|
| || || || |
Once you have completed the table with information gathered from the Internet, you should be able to answer the question: are birds really dinosaurs?
In the process of completing this WebQuest, you’ve become informed about the evidence linking birds with dinosaurs, and about new fossil discoveries that challenge the theory that birds evolved from theropods. You have developed critical thinking skills and you have explored the many different facts that relate to the question of the origins of birds. You have read information to complete a table about bird and birdlike fossils, and formed an educated opinion as to the origins of birds. Are birds really dinosaurs?