Welcome to Hell Creek in South Dakota. The temperature hovers between 43[degrees]C and 52[degrees]C (110[degrees]F and 125[degrees]F). There's no shade--or anything else for that matter, but dust and rocks. For six weeks in 1990, paleontologist Susan Hendrickson and a crew from the Black Hills Institute of Geological Research picked away at these badlands in search of dinosaur fossils.
On what was supposed to have been their last day in the field. August 12, 1990, Hendrickson hiked off alone toward an outcrop she had yet to explore. Five kilometers (three miles) out, at the base of a 15 meter (49 foot) cliff, she spied dark-brown fragments of fossilized bone amid gray mudstone (rock made of mud or silt) and yellowish sandstone (rock made of sand).
The fossils were three huge vertebrae, or bones that make up the spine, likely belonging to a Tyrannosaurus rex. "I knew immediately!" says Hendrickson. "The bones were big; and T rex was likely the only large carnivorous [flesh-eating] dinosaur that lived in the area in the late Cretaceous Period." Dinosaurs may once have roamed the entire Earth, but T rex lived only in what is now western North America.
The skeleton, named Sue in Hendrickson's honor, turned out to be the largest, most complete, and best-preserved T rex found to date. This year marks the 20th anniversary of Sue's discovery. Follow this famous dinosaur's story, from her life millions of years ago to her excavation and reconstruction.
PEEK AT THE PAST
Flash back to 67 million years ago. South Dakota looks nothing like it does today. Gone is the dry and desolate landscape: The area is lush and damp. Overhead, a giant reptile with a 12 m (39 ft) wingspan soars on an updraft. A group of three-horned dinos called triceratops lazily munch succulent ferns and flowering herbs. Nearby, a herd of hadrosaurs--hefty, duck-billed dinosaurs--wallow in a muddy river.
Suddenly, the ground rumbles. An earthquake? No! Plowing through the ferns--head down, tail straight out, legs pumping--comes a colossal T rex. The hadrosaurs scatter, but one's not fast enough. The T rex uses its short, two-clawed forelimbs (arms) to slam the duckbill into a cinnamon tree and chomps into its back. Dagger-like teeth cleave flesh and bone. It's just another eat-or-be-eaten day in the late Cretaceous Period.
Twenty years later, the same T rex is sick. Lumbering down a riverbank, it collapses and dies. The river floods and the torrent of water hurls the dinosaur's pelvis (bone to which the legs attach) onto its head. The current buries the twisted heap of rotting flesh and bone in fine sand and mud. As millions of years pass, layer after layer of sediment piles atop the bones. The weight pressing down forces water through tiny spaces in the T rex bones; minerals collect in the spaces. Eventually, the bones become the rock-hard fossilized remains of Sue.
WHO WAS SUE?
When Hendrickson unearthed Sue, she knew she was looking at a late Cretaceous fossil. "You can tell a fossil's age by the layer of earth in which it's deposited--give or take a million years," she says. Rock layers are windows into specific time periods (see Nuts & Bolts, above). Sue's fossilized bones not only tell a lot about when she lived, but also how the dinosaur lived and died.
Scientists still can only speculate on whether Sue is really a she. But some believe that female T rexes were bigger than males. Since Sue is the biggest T rex found to date, "she's probably a female," says Hendrickson. "And I really hope she stays that way!"
Amazingly, after all the time since Sue's death, it's still possible to see where muscles, tendons, and other tissue attached to her bones. Sue was 28 years old when she died, making her the oldest T rex ever discovered. Some vertebrae are fused together, a sign of arthritis (inflamed-joint disease). Some ribs broke and healed in her lifetime. Her diseased left fibula (lower leg bone) had a big pus pocket.
FEARSOME HUNTER
It's believed T rex scavenged some food, but the dinosaur was primarily built to hunt. Two thirds of each of T rex's 30.5 centimeter (12 inch)-long teeth is embedded in jawbone. These are teeth designed to tear into live flesh.
X-rays of Sue's skull reveal that her olfactory bulbs (odor-detecting regions of the brain) were as big as her football-size brain. "Sense of smell is critical for hunting, and T rex smelled its way through life," says Bill Simpson, who manages the fossil collection at the Field Museum of Natural History in Chicago.
Between her neck and rib cage, Sue also has an enormous forked wishbone, or furcula, similar to those found in birds. It's the first intact furcula found in a Trex--key evidence linking the evolution of birds to carnivorous dinosaurs. Details like these help scientists reconstruct how Sue might have looked and moved.
DINO JIGSAW PUZZLE
It took three weeks for Hendrickson's team to uncover Sue's bones and wrap them in cloth and plaster casts. As they moved the massive but fragile bones still encased in matrix (rock that surrounds fossils) into trailers for transport, the number of bones stunned them. With more than 250 bones, 90 percent of Sue's skeleton is accounted for.
In 2000, all 6,350 kilograms (14,000 pounds) of Sue's cleaned, fossilized bones were assembled and put on display at Chicago's Field Museum of Natural History. "I worried Sue wouldn't live up to expectations," Hendrickson says. "But she didn't let us down. I still get chills when I see her." The 16 million visitors who've come to marvel at Sue over the last decade would undoubtedly agree.
T. REX TOOTH: This is the actual size of one of Sue's teeth. It's designed to tear into flesh.
nuts & bolts
GEOLOGICAL TIME
Geologists know about ancient life from fossilized remains of organisms buried in layer upon layer of rock or sediment. This geological time chart reveals the layers and the sequence of fossil history.
PRECAMBRIAN ERA: Earth formed. The first single-celled life-forms appeared 3.6 billion years ago (bya). Continents took shape about 3 bya.
PALEOZOIC ERA: Algae and other boneless life-forms filled the oceans. Crustaceans and fishlike animals appeared. Simple plants grew on land, then giant ferns, and later vast conifer forests. By 290 million years ago (mya), reptiles evolved.
MESOZOIC ERA: In the Jurasic Period, dinosaurs and the first birds evolved. By the Cretaceous Period, small mammals appeared, and T. rex ruled North America. Dinosaurs died out at the end of the Mesozoic Era.
CENOZOIC ERA: Mammals diversified, and birds flourished. Continents took on their present forms. Modern humans appeared late in the Quaternary Period.
video extra
For a time-lapse video of Sue's skeleton being assembled, visit: www.scholastic.com/sciencworld
EARTH: Fossils
T. rex Brought to Life
PRE-READING PRDMPTS:
* What are fossils? How do they form?
* How long ago was the Cretaceous period? Can you name three dinosaurs that roamed the earth during this era?
* Why do scientists think birds may be related to carnivorous dinosaurs?
DID YOU KNOW?
* Paleontologist Richard Owen coined the term dinosaur in 1842. It means "terrible, powerful, wondrous lizard" in Greek. The name Tyrannosaurus rex means "tyrant lizard king" in Greek.
* Dinosaur eggs came in all shapes and sizes. Some were as small as tennis balls; others were as large as footballs.
* In addition to eating the flesh of its prey, the T rex probably also ate the prey's bones. Paleontologists have found bone fragments in fossils of T rex dung.
CRITICAL THINKING:
* Paleontologists in North Dakota recently made a rare discovery: a 66 million-year-old hadrosaur skeleton with fossilized skin still attached. How do you think the dinosaur came to be so well-preserved? What do you think scientists can learn by studying this unique find?
PROJECT-BASED LEARNING:
HISTORY/ART: Pick one of tile geological eras in the diagram on pp. 8-9 of the Student Edition. Research the plants and animals that thrived during this time period. Then draw or paint a scene depicting these creatures in their natural habitat. Take it further by displaying the scenes on the bulletin board in chronological order to see how Earth has changed over time.
Source Citation
Masibay, Kim. "T. rex brought to life: step back in time and meet Sue, one of the largest beasts ever to walk Earth." Science World 8 Nov. 2010: 6+. General OneFile. Web. 27 Nov. 2010.
Document URL
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