ContentsFlying Beasts The Age of Archosaurs A Different Earth Adapting to Change Bird Fossils Revealing Evidence Ornithologists Bird Groups Birds Closeup Life Cycle of Birds Disappearing Act Digging for Birds Further Research Quiz Glossary Index 4 6 8 9 10 12 13 14 16 18 22 26 28 30 31 32
Feeding Habits of Birds . . . . 20 Prehistoric Birds Onscreen . . 24
Ancient Activity . . . . . . . . . . 29
Flying Beastsirds have lived on Earth for a long time. When dinosaurs roamed the world, prehistoric birds also filled the skies. Scientists think the first birds appeared on Earth about 150 million years ago, during the Late Jurassic Period. There were many types of prehistoric birds. They ranged in size from very small to very large. Many died out along with the dinosaurs at the end of the Cretaceous Period, about 6^ million years ago. Even though many birds disappeared, others continued to live and are still living today.
Pterosaurs were flying reptiles, not birds. They had wings, but no feathers. A leather membrane covered their wings. Their wings ranged in size from a few inches to more than 40 feet (12 m).4 FLYING BEASTS
Albertosaurus\N3S a theropod, which means "beast footed." Most theropod dinosaurs walked on two legs.
Today, many paleontologists believe that birds actually evolved from a type of dinosaur called a theropod. Theropods were meat-eating dinosaurs that shared many features with modern birds.
FACTS ABOUT FLYING ANIMALSThe largest known flying animal was Quetzacoatlus, a member of the pterosaur family, it had a wingspan of 40 feet (12 m) or more. Quetzacoatlus \N3sf'\[s\ discovered in Big Bend National Park, Texas, in 1971. Some scientists are not sure if the Archaeopteryx, the first known bird, used its feathers to keep its body temperature normal or if it used its feathers for flight.
The Age of Archosaursor more than 3.5 billion years, living things have grown and developed on Earth. Scientists have divided Earths history into blocks of time called eras. The eras are divided into periods. The dinosaurs lived during the Mesozoic Era, often called the "Age of Dinosaurs."
PALEOZOIC ERA545 Million to 250 Million Years Ago
^ Paleozoic means "ancient life." During this era, more complex life forms appeared on Earth, including fish, insects, land plants, and reptiles.Algae fossils
4.6 Billion to 545 Million Years Ago
During the Precambrian Era, simple life forms first appeared in the seas.
Trilobite fossils6 THE AGE OF ARCHOSAURS
Some scientists think the Mesozoic Era should be called the "Age of Archosaurs." The archosaurs were a large group of animals that included birds, dinosaurs, and pterosaurs, or flying reptiles. The first known bird was the Archaeopteryx. It is thought to have appeared at the end of the Jurassic Period about 150 million years iigo. The Archaeopteryx shared features with the birds that are alive today and dinosaurs. It had bird-like features, such as feathers, wings, a wishbone, and light, hollow bones. It also had dinosaur-like features, such as a full set of teeth, a long tailbone, and three claws on each wing.
CENOZOIC ERA65Million Years Ago to the Present Cenozoic means "recent life." All types of mammals began to appear on Earth during the Cenozoic Era.
250 Million to 65 Million Years Ago Mesozoic means "middle life." Dinosaursand birds appeared during the Mesozoic Era. By the end of this era, many of these animals became extinct.
Oldest-known hat fossil
A Different Earthuring the Mesozoic Era, when birds first appeared, Earth was much warmer than it is today. In the Triassic Period, the land on Earth formed one large continent called Panguea. The climate was warm, the sea level was high, and there was no ice at the North Pole or South Pole. During the Jurassic Period, Pangaea began to divide into separate continents. The climate grew moist, and forests became thicker. In the Cretaceous Period, the land continued to shift and change. The climate was warm, and there were wet and dry seasons. By the end ofthe Cretaceous Period, the continents looked much like they do today.
THE CHANGING CONTINENTS
Triassic Period One continent called Pangaea
Jurassic Period Pangaea begins to break apart
Cretaceous Period Modern continents begin to form
A DIFFERENT EARTH
Adapting to ChangeThe Dodo's hooked beak may have been used to catch fish. The Dodo lacked the strong chest muscles needed for flight.
The Doc/o did not need to fly, so it developed small, weak wings.
s Earth changed, animals adapted to fit into their environment. Paleontologists agree that the first bird was the Archaeopteryx, but after that, they disagree about the history of birds. Some scientists think that birds evolved from meat-eating dinosaurs called theropods. Today's birds share many features with ancient theropods, including light, hollow bones. Other scientists believe that birds evolved from early reptiles called thecodonts. Crocodiles, dinosaurs, and pterosaurs all evolved from archosaurs.BIRDS 9
rehistoric birds lived on Earth a long time ago. It is not possible to go back in time to see them. It is possible to learn about them by looking at their fossils. Fossils are the rocklike remains of ancient animals and plants. Some fossils are bones and shells, and other fossils are impressions of feathers, leaves, and skin. Feather impressions found in ancient rocks have helped scientists identify prehistoric birds such diS Archaeopteryx.
Hardened tree sap, also called amber, can preserve items so well that even the individual fibers of a feather are visible.10 BIRD FOSSILS
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Sedimentary rock, where many fossils are found, is made of strata, or layers. Exposed sedimentary rock often can be found on cliffs and riverbanks or in desert badlands.
HOW FOSSILS ARE FORMEDPaleontologists have found the fossils of many different prehistoric animals. A fossil is created when layers of mud and sand cover the bones of an animal that has died. As time passes, layers of mud build up. The weight of the upper layers of mud pushes down on the lower layers to form solid rock. Bones or plant materials become fossils. Bird fossils afe not as common as dinosaur fossils. Birds had light, hollow bones that did not always last long enough to become fossils After a bird died, it sometimes rotted away or was eaten by other animals before its bones could get trapped in mud.
Revealing Evidencevery new fossil helps paleontologists understand what life was like on Earth long ago. By looking at fossils, scientists can get a better idea of how large an animal was, when it lived, whether it walked on the ground or flew through the air, and if it lived alone or in a herd. Paleontologists are much like detectives. They try to learn as much as they can from the evidence, or clues, they find. In order to identify a bird fossil, paleontologists look for special features, such as impressions of feathers, a wishbone, or bird-like hips. These are the features that prehistoric birds such zs Archaeopteryx had in common with modern birds.Scientists think that Archaeopteryxy^3s a weak flier. It probably was best at gliding, leaping, and running.
Ornithologistsn ornithologist studies birds. They may study the behavior of birds, where birds live, and how birds interact with their environment. Ornithologists may also be involved in saving birds that are in danger of becoming extinct. Ornithologists can work for government agencies or other organizations. They may work with wild birds, in a laboratory, or on their computer. Some study a particular bird group, while others are interested in all birds. Ornithologists perform many different types of jobs, and they use a variety of tools. If they work in the field, they may use binoculars, telescopes, and nets or traps. If they work in a laboratory, they may use microscopes, test tubes, cages, and computers. To become an ornithologist, you need to do well in science and math classes. You should also develop the language skills necessary for writing reports.
Ornithologists sometimes catch and tag birds in order to track their migration patterns.BIRDS 13
irds can be divided into two major groups: the advanced fliers and the flightless birds. Scientists believe that the type of dinosaur most closely related to birds is a group of dinosaurs called theropods, a group of bipedal dinosaurs. Theropods share so many features with today's birds that some scientists believe that birds actually are theropod dinosaurs. One very bird-like dinosaur was the Deinonychus. This dinosaur did not have feathers and could not By, but its distinctive hipbone is similar to the hipbone of a modern bird. This has led scientists to believe that modern birds evolved fromDeinonychus, or a dinosaur
very much like it.
The hipbone of theropods allowed them to stand and walk upright. Modern birds have the same type of hipbone.14 BIRD GRDUPS
ADVANCED FLIERS: NEOGNATHOUS BIRDSMost modern birds belong to the neognathous, or advanced fliers, group. Many scientists believe that all birds developed features for flight Birds needed to be very light to get off the ground and stay off the ground, so they developed hollow bones. They also needed to stay in the air once they were in the air. That is why birds developed wings and feathers. How Deinonychusr]\qhX have developed into an animal that c