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Tyrannosaurus Rex
Photograph © The Field Museum, #GN89860_3c
Tyrannosaurus rex arose during the Cretaceous period about 85 million years ago and thrived as a top land predator until the dinosaurs went extinct 20 million years later. This skeleton, on display in Chicago's Field Museum, is a cast of perhaps the world's most famous fossil: "Sue," a 67-million-year-old T. rex discovered in 1990 in South Dakota by field paleontologist Sue Hendrickson. It is the most complete, best preserved, and, at 42 feet (12.8 meters), the largest T. rex specimen ever found.
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Triceratops Movement
Image by Smithsonian Institution/Photo Researchers, Inc.
Computer models show how a massive Triceratops likely walked. The sequence, which used digital scans of an actual fossil skeleton, was part of a 2001 million-dollar project by the Smithsonian National Museum of Natural History to accurately remount its nearly 100-year-old Triceratops specimen.
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Dinosaur Models
Photograph by Jonathan Blair/Corbis
Awaiting renovations, dinosaur models of differing scales crowd a warehouse at Dinamation headquarters in Irvine, California. Some of these specimens would have seen their heyday during the Cretaceous period, including the familiar Tyrannosaurus and Triceratops, the Parasaurolophus (front right), and the flying pterosaur (top left). Others, like the stegosaurids (front center), were already extinct when the Cretaceous began.
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Cretaceous Collection
Artwork by Publiphoto/Photo Researchers, Inc.
This rendering of Cretaceous life shows the diverse range of dinosaurs that lived between 145 and 65 million years ago, including maiasaurs (front left); tarbosaurs (top right), and pterosaurs (top center). In the foreground are depicted the first flowering plants and one of the earliest mammal relatives, both of which developed during this period and went on to survive the dinosaur extinction at the end of the Cretaceous.
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Chalk Cliffs
Photograph by Norbert Rosing
The chalk cliffs on Germany's Rügen Island rise 330 feet (100 meters) or more over the Baltic Sea. These ancient structures are made nearly entirely of the skeletons of calcite-covered plankton called coccolithophores, deposited by the trillions during the Cretaceous period. Sediments like these actually give the Cretaceous its name: Creta means "chalk" in Latin.
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Madagascar Fossil
Photograph by Maria Stenzel
A paleontologist brushes dirt from a bit of fossilized bone in Madagascar. Madagascar is awash in fossils from the Cretaceous period, when the island broke off from Africa and later split in two. Part of the landmass stayed close to Africa and became Madagascar. The other moved northeast, eventually colliding with Asia and forming the Indian subcontinent.
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Cocosphere
Photograph by Andrew Syred/Science Photo Library
This scanning electron microscope image reveals the intricate patterning of ancient coccolithophores, microscopic plankton abundant in shallow seas during the Cretaceous period. As these organisms died, their skeletons, called cocospheres, fell by the trillions to the seafloor, forming layer upon layer of calcium carbonate. Millions of years of pressure and heat turned these layers into the chalk we use today in our everyday lives and helped preserved countless fossils from the Cretaceous.
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Flying Pterosaurs
Artwork by Mauricio Anton/Science Photo Library
Pterosaurs, like these depicted gliding near an ancient sea, first arose during the Triassic period about 215 million years ago. They endured for 150 million years, colonizing every continent and evolving into more than 120 species. They died out along with the dinosaurs at the end of the Cretaceous.
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Sapeornis Chaoyangensis
Photograph by O. Louis Mazzatenta
This Sapeornis chaoyangensis fossil, housed in a Beijing museum, offers clues about the feeding habits of the Earth's early birds. The presence of gastroliths—stones ingested by animals to grind food in the gut—indicates that this species was a plant-eater. Other significant features include exceptionally long forelimbs, suggesting that Sapeornis, the largest known bird from the early Cretaceous, might have been able to soar.
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Pterosaur Fossil
Photograph by Jonathan Blair
Like their cousins the dinosaurs, pterosaurs stand out as one of evolution's great success stories. They first appeared during the Triassic period, 215 million years ago, and thrived for 150 million years before going extinct at the end of the Cretaceous period. Uncontested in the air, pterosaurs colonized all continents and evolved a vast array of shapes and sizes. This specimen, found in Italy, is Eudimorphodon ranzii, with a wingspan of about three feet (one meter) and 114 tiny teeth packed into its jaws.
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