|
|
|
THE ORIGINS OF BIRDS
Introduction
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.
Top
Task
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?
Top
Resources
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.
Top
Time
2 class periods; a total of 60 minutes for Internet
research, 20 minutes to prepare table and answer
question
Top
Process
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 |
Age
(millions of
years)
|
Location |
Important Facts |
|
Longisquama |
220 |
Kyrgyzstan |
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 |
|
Archaeopteryx |
150 |
Germany |
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?
Top
Conclusion
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?
Top
| |
|
