When dinosaurs dominated: ancient creatures arrive from China: A new exhibition "tells the story of how the planet changed while dinosaurs ruled the Earth--and how this affected the evolution of dinosaurs and other life.

• Position: The World Yesterday

"DINOSAUR DYNASTY: Discoveries from China" introduces North American dinosaur enthusiasts to the prehistoric creatures that ruled large tracts of Asia for 165,000,000 years. The exhibition features fossils and life-size cast reproductions from all three periods of the Mesozoic era: Triassic, Jurassic, and Cretaceous. On display are dinosaur eggs and nests, as well as a variety of plants and animals that lived in the shadow of these giants. Visitors will meet Mamenchisaurus, a huge plant-eater with the longest neck of any animal in history; the unicorn-like duck-billed Tsintaosaurus; and a miniature ceratopsian called Psittacosaurus, or parrot lizard; Sinosauropteryx and Caudipteryx, two of the feathered dinosaurs that have electrified the world of paleontology--and who can resist the sight of a Monolophosaurus locked in mortal combat with a Tuojiangosaurus?

It is no accident that China is where some of the best preserved, most abundant, and diverse dinosaurs are located. "To get good preservation, you need an area where sediments are being deposited at a reasonably high rate, to give material a good chance of fossilizing," explains Peter Makovicky, dinosaur curator at The Field Museum, Chicago. "China had several episodes of tectonic shifting throughout the Mesozoic era, forming mountains separated by basins and creating a lot of fossil-bearing sediment." Although dinosaur fossils are found on every continent, including Antarctica, the best conditions in the past--and the best dinosaur finds today--are in China, western North America, Argentina, and Saharan Africa.

What is important about good preservation, points out Makovicky, is what researchers can learn from the minute details it reveals. For example, scientists were very excited to discover the clear impressions of primitive, filament-like feathers growing from the skin of the Sinosauropteryx. They could see that these were not true flight feathers, but simpler structures--similar to the insulating down feathers of modern birds--that could have evolved into feathers. Because Sinosauropteryx is not as closely related to birds as some other dinosaurs are (Velociraptor, for example), the presence of these downy structures told them that feathers began to evolve in dinosaurs long before the origin of birds.

"Dynasty" also tells the story of how the planet changed while dinosaurs ruled the Earth--and how this affected the evolution of dinosaurs and other life. "We begin in the Triassic period, when Earth had just one super-continent, Pangaea," says exhibition project manager Cheryl Bardoe. "The diverse reptiles of this period gave rise to tortoises, crocodiles ... and the earliest dinosaurs." The exhibition continues through the Jurassic period, when dinosaurs truly dominated the land. During this time, Pangaea began to fracture, seas opened up and, in a geographically isolated area that now is China, dinosaurs took their own evolutionary path. Around the world, they developed new features adapted to their habitats: spoon-shaped teeth for chomping tougher leaves, strong leg and tail muscles for standing to graze on higher branches, and serrated teeth for ripping into prey.

"Adaptation is why we see Chinese dinosaurs that are similar to--but not exactly the same as--those we find in North America," Makovicky notes. "Mamenchisaurus instead of Diplodocus, for example, or Monolophosaurus instead of Allosaurus."

In the Cretaceous period, the continents began to split apart and the climate cooled. Dinosaurs, in China and elsewhere, became even more diverse, including bird-like dinosaurs and dinosaur-like birds. They now shared the land with small mammals and flowering plants. When a disaster--like a meteor crash...