Dinosaurs EXPLORE THEIR MYSTERIES

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1 Dinosaurs EXPLORE THEIR MYSTERIES Dinosaurs are among the most mysterious and captivating animals ever to live on Earth. Experience the ways our scientists have assembled answers to many fascinating questions about their lives and their world. What are dinosaurs? Large and small, ferocious and mild, lumbering and quick, dinosaurs first appeared more than 230 million years ago. These astonishing reptiles lived on land and would eventually conquer the air. How do we study dinosaurs? We ve learned most of what we know about dinosaurs from their fossils. Scientists use a wide range of techniques to find, collect, analyze, and interpret fossils. The results lead to new discoveries and an ever-clearer picture of what dinosaurs looked like and how and where they lived. The Museum s Dinosaur Institute is dedicated to advancing our understanding of dinosaurs.

2 What can we learn from fossils? Very few plants and animals leave fossils when they die. But under the right conditions, bones, teeth, eggs, skin impressions and footprints become fossils. These rocky remains give us the only direct evidence of dinosaurs and other ancient life. They tell us what dinosaurs ate, how they lived and what the world they lived in was like. Immense in size and bizarre in appearance, dinosaurs are wrapped in mystery and lost in time. We piece together clues we find in dinosaur fossils to bring these puzzling animals to life.

3 One Triceratops built from four Look at this skeleton. It may seem like the bones all came from one animal, but they didn t. We rarely find complete dinosaurs. Instead, we have to mix and match bones from several specimens to build a skeleton like this. So while you see one Triceratops here, it includes bones from four different animals collected by Museum scientists from several locations.

4 How diverse were dinosaurs? One mark of evolutionary success for all forms of life is how diverse and varied a group becomes. Studies of their fossils and their living relatives have shown that dinosaurs were and still are surprisingly diverse in size, diet, appearance, and lifestyle. That makes them one of the most successful groups of large animals ever to walk the Earth. Dinosaurs large and small Dinosaurs include the largest animals ever to walk the Earth. Some, like the Mamenchisaurus pictured above, grew more than 70 feet long and could weigh many tons. But not all were giants, Fruitadens, one of smallest known species, grew to just over 2 feet long and tipped the scales at less than 2 pounds.

5 Herbivores, carnivores, and omnivores Many dinosaurs, including Lambeosaurus, were herbivores that ate only plants. Others, like the infamous Tyrannosaurs, were carnivores that preyed on other animals. Still others were omnivores that ate a more varied diet. Scientists believe that Fruitadens, for example, ate plants as well as bugs and some small animals. Two legs or four? We once thought all dinosaurs plodded along on all fours. Some, like Brachiosaurus, did walk in that way. But we now know that others, like the Thescelosaurus, walked on two legs, a posture that allowed them to move more swiftly. And some likely switched between the two postures.

6 What was their world like? If you went back to the Age of Dinosaurs, you d find an unfamiliar scene. The climate was warmer, and the continents were locked together as one. You d see reptiles flying in the air and swimming in the seas. And on land, you d find dinosaurs in an incredible variety of shapes and sizes. What lived in the ancient oceans? While dinosaurs walked the land during the Mesozoic, the warm oceans teemed with a variety of other animals, including huge sharks, toothed birds, and the largest-ever bony fish and turtles. Some groups, including giant marine reptiles and ammonites, have gone extinct. But many others still live today.

7 Life in the Western Interior Seaway Around 85 million years ago, a large inland sea known as the Western Interior Seaway split what is now North America in two. How do we know that diverse prehistoric life inhabited these warm waters? Much like investigating Mesozoic life on land, we gather information from fossils in rocks laid down on the seafloor millions of years ago. Polycotylus latippinus Unlike dinosaurs, plesiosaurs gave birth to live young, which indicates that they lived entirely in the water, never venturing onto land. The specimen on the wall shows that plesiosaurs gave birth to a single large baby. If this baby has been born, it would have been close to 40 percent the size of its mother which is very unusual in reptiles.

8 What were they like? Today we know dinosaurs only from fossils. But these old bones and bits of skin once belonged to living, breathing animals. They hunted for food and fled from danger. They sought mates and cared for their young. They suffered diseases and injuries. They faced life s challenges just as we do today. Meet Thomas the T. rex Thomas, the largest T. rex on this platform, is one of the 10 most complete T. rex specimens ever found. Fewer than 50 partially complete skeletons have been discovered and four of them are right here at the Natural History Museum! So far, there is no way to tell if Thomas was male or female. So why Thomas? In 2003, high school teacher Robert Curry discovered T. rex fossils poking out of the ground in a remote part of Montana. He named the animal after his brother Thomas, who had shared his love for fossil-hunting ever since they were young boys.

9 Different species or different ages? This scene shows three T. rex individuals of different ages gathered around the partial carcass of a duck-billed dinosaur. Based on differences in the shape and proportions of their bones, some scientists once thought these were three separate species. It wasn t until we studied their bone tissue that we realized they were different life stages of probably just one species. Tyrannosaurus rex The largest specimen, nicknamed Thomas, is one of the most complete T. rex skeletons found so far. It was around 17 years old when it died, which means it wasn t yet fully grown. The smallest specimen, thought to be only 2 years old when it died, this is the youngest T. rex specimen found to date. We don t know for sure, but scientists think that Tyrannosaurus young may have been feathered. Remains of a juvenile T. rex are rate. This third specimen juvenile was around 14 years old when it died. It s unclear what size prey juveniles could kill; the answer depends in part on whether they hunted alone or in groups.

10 Changes over time Scientists divide the long history of the Earth into units based on changes in ancient life over time. Different groups of dinosaurs shared their world with many other reptiles in each of the three periods of the Mesozoic Era, also known as the Age of Dinosaurs. These were the Triassic (251 to 200 million years ago), the Jurassic (200 to 145 million years ago), and the Cretaceous (145 to 65 million years ago). Triassic Period (251 to 200 million years ago) The first dinosaurs evolved during the Triassic. These were mostly small meat eaters. They shared their world with a host of other reptiles, many of which were larger and more abundant. From this humble start, dinosaurs began to evolve diversify. Jurassic Period (200 to 145 million years ago) Dinosaurs flourished during the Jurassic, branching out into many new groups and species. Some of the largest dinosaurs evolved during this time. Among them were plant eaters such as the heavily armored Stegosaurus and predators such as Allosaurus. Cretaceous Period (145 to 65 million years ago) Dinosaurs continued to thrive during the Cretaceous. Duckbilled dinosaurs such as Edmontosaurus evolved during this time, as did Triceratops and many other horned dinosaurs. Near the end of the period, Tyrannosaurus rex hunted its prey in what s now western North America. But the end of the period brought the end of the remaining large dinosaurs.

11 What caused the extinction of large dinosaurs? Around 65 million years ago, nearly half of the plant and animal species including the last of the large dinosaurs became extinct. A giant asteroid hit the Earth at the end of the Age of Dinosaurs. But scientists still disagree whether this was the sole cause of the mass extinction that took place or if there were multiple causes. What happened to dinosaurs? Throughout the Age of Dinosaurs, hundreds of species of dinosaurs flourished and hundreds became extinct. Tyrannosaurus rex, among the last of the large dinosaurs, died out some 65 million years ago. But birds including the gulls and pigeons you see outside the Museum descended from relatives of the might T. rex!