Vertebrate Paleontology at the American Museum of Natural History
For the last 131 years paleontologists from the American Museum of Natural History have scoured the globe in search of fossils. In the late 1890s, Barnum Brown, the Museum's foremost dinosaur collector, searched Western North America and brought home many of the dinosaurs on display: Apatosaurus, Tyrannosaurus, Triceratops, Saurolophus, and Ankylosaurus. In the 1920s, Roy Chapman Andrews led expeditions to the Gobi Desert of Mongolia, where incredible fossils, both of dinosaurs and early mammals, were unearthed. Today, the tradition of fieldwork continues. In the last ten years, expeditions from the Department of Vertebrate Paleontology have traveled to every continent in search of dinosaurs and other fossils. They have returned to the Flaming Cliffs of the Gobi Desert to continue where Roy Chapman Andrews left off almost 70 years ago. These yearly expeditions have uncovered extraordinary fossils, including an oviraptor sitting on a nest of eggs and a dinosaur embryo nestled in its egg. These important finds are among the 600 specimens on view in the Museum's Fossil Halls on the fourth floor. Two of the Halls house the Museum's dinosaur collection. These dinosaurs are more than just specimens. They are invaluable not only because of their rarity, aesthetic quality, and number, but because of the historical link between these fossils and our understanding of vertebrate history.

The Evolution of Dinosaurs
Dinosaurs are part of an evolutionary chain that stretches back more than 500 million years to the origin of vertebrates — the first animals with backbones and braincases. About 380 million years ago, the first tetrapods, or four-footed vertebrates, ventured out of the water on newly evolved stout limbs with distinct ankles, wrists, fingers, and toes. Not until 310 million years ago did the watertight egg evolve in vertebrates. These vertebrates are called amniotes. The watertight egg keeps the embryo from drying out and dying when eggs are laid on land.

About 10 million years later, two distinct lineages evolved: one led toward synapsids (mammals), the other to sauropsids (reptiles), which include turtles, lizards, snakes, crocodiles, pterosaurs, birds, and dinosaurs. The feature that sets dinosaurs apart from other sauropsids is a hole in the hip socket. The hole in the hip socket allowed dinosaurs to stand with their legs directly beneath their bodies. Because of their upright stance, dinosaurs may have been able to run more efficiently and with more stamina. This may have given them the advantage of outlasting prey in a chase or outmaneuvering predators. More primitive sauropsids, such as crocodiles and lizards, have legs that sprawl out to the sides. When "sprawled-out" animals run, they have a side-to-side motion, like a waddle. Dinosaurs dominated the land until about 65 million years ago when an episode of extinction eliminated the dinosaurs (except for modern-day birds) as well as many other plants and animals, both on land and in the sea.

The Museum Experience
As you and your students tour the two Dinosaur Halls, you will be following the evolutionary development of two distinct groups of dinosaurs, the Saurischians and Ornithischians. A black path on the floor of each Hall will guide you through the evolution of the particular group. Along the path are columns that highlight each new feature that evolved, such as a grasping hand or an uneven covering of enamel on the teeth. At each column you can walk off the main path to explore in more depth the development of the feature and the group of closely related animals that share it.

During their museum experience your students will enhance their overall understanding of dinosaurs; examine certain features of dinosaurs in order to draw conclusions about what they ate, how they moved, and how they cared for their young; and explore the various theories as to how these animals (except for modern birds) became extinct.