Assign each student to a group. Direct groups to the Hall of Saurischian Dinosaurs and the Hall of Ornithischian Dinosaurs. In addition, groups should visit the Barosaurus displayed on the second floor in the rotunda. Suggest groups visit the other Fossil Halls if time permits. Use the following information along with the map of the Halls to guide your students through the exhibition. Museum Explainers are available throughout the Halls to answer your questions. A cart with touchable fossils can also be found in the Halls.

Only the animals displayed in the Halls of Saurischian and Ornithschian Dinosaurs are actually dinosaurs. Animals in the Hall of Vertebrate Origins, such as pterosaurs and mosasaurs, are not dinosaurs.

1. Column: Hole in the Hip Socket | All dinosaurs share the characteristic of a hole in the hip socket. This feature is related to an upright or erect posture. The legs of dinosaurs are directly beneath their hips. Other reptiles have legs that sprawl out to the sides. This upright stance may have allowed dinosaurs to move more quickly and with more endurance.

2. Excavation/Preparation | This exhibit takes visitors behind the scenes where they can examine how fossils are found, excavated, prepared, and displayed. This fascinating account will answer many of the questions students have about how dinosaurs are excavated and prepared and introduces them to Museum scientists.

3. Cladograms | The Halls feature the evolution of dinosaurs, the animals that dominated the Earth for over 150 million years. In them, you can see fossils of every major group of dinosaurs that has ever lived, including birds. The cladograms illustrate how dinosaurs are related.

The Hall of Saurischian Dinosaurs
The Saurischian dinosaurs, or lizard-hipped dinosaurs, share the feature of a grasping hand. Saurischian dinosaurs include the plant-eating sauropods and the carnivorous theropods.

Coelophysis, located in the case to the right as you enter the Hall, is one of the early meat-eating dinosaurs. Mass graves of these animals have been found, indicating they may have been victims of a sudden cataclysmic event, such as a flash flood. Bones of young Coelophysis have been found inside the body cavity of the larger animals. This indicates that Coelophysis was cannabalistic and fed on the young of its own species.

4. Column: Grasping Hand | Two hands are represented on this column. The lower one shows how hands looked before grasping hands evolved. Notice that the fingers are all about the same size. Now, look at the upper hand, which is the hand of a dinosaur called Plateosaurus. Here, the fingers are different lengths: the second finger is the longest, and there is a large, slightly offset "thumb." We call this feature a "grasping hand." It evolved in the first saurischian dinosaur. The feature was passed on to its descendants. It may be difficult for your students to imagine an Apatosaurus with a grasping hand. Ancestors of apatosaurs did have a grasping hand, but over millions of years that feature was transformed so that a heavy foot evolved.

5. Apatosaurus | Point out to students that Apatosaurus was once named Brontosaurus. With their gigantic bodies and long necks, apatosaurs are among the most familiar and easily recognized of all dinosaurs. They are the largest animals ever to walk on land. Their fossilized bones and those of their closest relatives have been found on every continent. Their roots are ancient, even for dinosaurs. Their remains have been found in rocks that are up to 225 million years old. All apatosaurs were plant eaters and must have consumed massive amounts of vegetation to maintain such huge bodies. The teeth of Apatosaurus and Diplodicus are found only at the front of the jaws. The teeth are shaped like pencil-sized cylinders. They may have been used for stripping leaves off branches.

6. Trackway | Behind the Apatosaurus is a trackway, footprints left by dinosaurs millions of years ago. Individual footprints from the Paluxy River trackway give us an idea of what the feet of some dinosaurs looked like. The front feet of one dinosaur (a relative of Apatosaurus) were large hoof-like pads. The hind feet were hoof-like as well, but the toes extended out, leaving separate imprints. Footprints of another dinosaur can also be seen — the three-toed foot of a theropod (a meat-eating dinosaur) that followed behind. Trackways are some of our most important clues to the ways dinosaurs lived. Because of trackways we can tell that some dinosaurs traveled in herds, can roughly estimate the speeds at which dinosaurs moved, and can understand something about the way they stood. This trackway tells us that the large dinosaur held its limbs directly below its body, like an elephant. Since there is no ridge between the footprints, the immense tail must have been carried completely off the ground.

7. The Carnosaurs: Allosaurus and Tyrannosaurus | The largest meat-eating animals ever to walk on land were the carnosaurs. With their huge heads, sharp claws, and knife-like teeth, they seemed to be ideally equipped for killing. The eyes of some carnosaurs may have faced forward, as our eyes do, rather than sideways, as in most dinosaurs. Forward-facing eyes provide an overlapping field of view (stereoscopic vision), which is important for judging distances and seeing accurately in low light. In addition, the carnosaur skull bones may have been able to move in relation to one another, like those of a snake. This would have allowed the animals to manipulate and swallow immense pieces of meat. Some scientists have suggested that carnosaurs did not hunt, but fed on rotting carcasses. We cannot be sure. All these ideas are based on scientists' interpretations of fossil bones that are often incomplete or have become distorted over millions of years. We may never have all the evidence needed to support these ideas.

Allosaurus | Re-creating the behavior of extinct animals is very difficult, and can only be done by accepting certain assumptions. These two skeletons are of animals that lived at about the same time and near each other. The Allosaurus may well have been a meat eater, as evidenced by its sharp teeth and large claws. Scratches and grooves on the tail of the Apatosaurus may have been made by an Allosaurus.

Tyrannosaurus rex | Tyrannosaurus rex was the largest and most fearsome carnivore of all time. Its pointed, knife-like teeth were ideal for slicing flesh. The lower jaw had a joint midway through its length that may have helped absorb the shock generated by struggling prey. Tyrannosaurus had very short arms that didn't even reach its mouth. Scientists have been unable to determine how Tyrannosaurus used its arms.

8. Maniraptors | Maniraptors are especially interesting because they include the relatives of dinosaurs that are living today — the birds. It was in the maniraptors that feathers originated from reptilian scales, and that flight evolved. Direct your students to find the specimens of Archaeopteryx, the oviraptorid egg with embryo, and the model of a Velociraptor. Also have them locate the modern-day birds on display (overhead).

The Hall of Ornithischian Dinosaurs
The Ornithischian dinosaurs share the feature of a backward-pointing pubic bone. The Ornithischian dinosaurs include the armored dinosaurs, the duck-billed dinosaurs and their relatives, and the horned and dome-headed dinosaurs. The Ornithischians were all plant eaters. Many had complex and often bizarre adaptations for defense, display, feeding, and locomotion.

9. Column: Backward-Pointing Pubis Bone | The feature Ornithischian dinosaurs share is the bottom-most bone in the group of three pelvic bones. This bone is the long one that extends way out to the left — which would be toward the rear of the dinosaur — and is called the pubis. It resembles the hip arrangement of birds, which is why these dinosaurs are called Ornithischians, which means "bird-hipped." After they were given this name, paleontologists concluded that birds, in fact, are related to the Saurischians (lizard-hipped dinosarus). So "bird-hipped" has proved to be a confusing misnomer.

10. Stegosaurus | Stegosaurs had elongated skulls and toothless snouts with inset tooth rows that formed cheeks farther back in their jaws. Stegosaurs walked on all four legs. Their name, which means "roofed reptile," refers to the prominent rows of plates and spines along the back. Scientists long assumed that the plates were to defend against attackers. The surfaces of the plates, however, are crisscrossed with grooves for blood vessels, indicating that they were covered with skin when the animal was alive. Some people speculate that the plates may have been used to control the animal's body temperature — cooling the blood when the animal was in the shade and warming it when in the sunlight. When Stegosaurus was first described in the 1890s, paleontologists placed emphasis on the animal's small brain cavity and the expansion of the spinal column in the pelvis. This gave rise to the completely incorrect idea that dinosaurs were so unintelligent that they needed a second "brain" to control the movements of their hind limbs, back, and tail.

11. Column: Uneven Tooth Enamel | Cerapods include duck-billed, horned, and dome-headed dinosaurs. The feature they all share is an uneven covering of the enamel on the teeth. It is thicker on the outside of the upper teeth, and on the inside of the lower teeth. As a result, when the animal chewed, the teeth wore down unevenly and developed sharp ridges. This allowed the dinosaurs to break down tough vegetation. Both the duck-bills and the horned dinosaurs independently evolved complex grinding or slicing surfaces called dental batteries that were composed of a thousand or more teeth. As old teeth wore down, new teeth grew to replace them. Direct your students to the skulls of these dinosaurs situated on the platform. There they can examine in detail how these dental batteries functioned.

12. Edmontosaurus | What we know about most extinct vertebrates comes solely from fossilized bones and teeth. This remarkable specimen is called a "mummy" because it also left impressions of skin and other soft tissues in the surrounding rock. It is mounted as it was found, lying on its back with the knees drawn up. The head and neck twisted backward as the tendons dried out. The discovery of the Edmontosaurus mummy, a duck-billed dinosaur, was more than a rare and exciting find. By studying the specimen, scientists learned that the skin was covered with tiny bumps, and not overlapping scales as in a snake's skin. In its stomach, scientists found the animal's last meal - pine needles, bark, and cones. Before this discovery, scientists believed that duck-billed dinosaurs lived near swamps and lakes and ate soft water plants. The mummy proved them wrong.

13. Anatotitan | Anatotitan was a duck-billed dinosaur. The duckbills were among the most widespread dinosaur groups. During the Late Cretaceous, about 70 million years ago, duckbills lived in North and South America, Europe, and Asia. Their habitats varied from forests in inland river valleys to swamps in coastal floodplains. In Montana, fossil deposits of a single species extend for miles and contain thousands of individuals, suggesting that hadrosaurs were very abundant in their habitats. Because of their duck-like beak and the webbing on the feet, duckbills were first thought to be aquatic, feeding on tender, lush vegetation. Duckbills, however, have powerful jaws with hundreds of teeth that were ideal for grinding fibrous land plants. This suggests that duckbills may have been more adapted to living on land.

14. Triceratops | This animal inhabited North America about 65 million years ago. Many paleontologists speculate that Triceratops traveled in herds and followed a seasonal route through the plains. Triceratops had a parrot-like beak, three horns, and a large bony shelf at the back of the skull, called a frill. The frill may have been used for defense or in mating displays.

15. Extinction | This exhibit examines the possible causes of extinction among large dinosaurs and many other plants and animals about 65 million years ago. Have your students examine the exhibit and decide which theory they support and why. There is abundant geologic evidence that at the end of the Age of Dinosaurs, a major episode of volcanic activity spewed out lava across a huge region of India. There is also evidence that a large asteroid or comet struck the Earth near the Yucatán, Mexico, around the same time. Either event could have increased pollutants in the air, altered temperatures, reduced sunlight, generated acid rain, adversely affected plant life, and eventually killed off the non-avian (non-bird) dinosaurs. The effects of the asteroid impact are thought to have lasted over a period of a few months. The effects of the volcanic eruptions could have lasted as long as millions of years. Scientists cannot pinpoint events that occurred in that period on a year-to-year basis, so they are unable to determine whether it was the asteroid impact or the volcanic activity, or both, that killed off the dinosaurs.