Hall of Saurischian Dinosaurs
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Together, the Hall of Saurischian Dinosaurs and the Hall of Ornithischian Dinosaurs continue the story of vertebrate evolution with the single largest collection of real dinosaur fossils in the world. These halls draw on the latest scientific research to show how the understanding of these fascinating creatures has changed significantly in recent years. Visitors can review the latest scientific findings and determine their own answers to such hotly debated questions as: Did dinosaurs care for their young? Did they live in social groups? Were they intelligent or slow-witted? How did they evolve? What caused most of them to die out? Organized to reflect evolutionary relationships, the Hall of Saurischian Dinosaurs examines the branches of dinosaurs that possess the trait of a grasping hand. The Hall of Ornithischian Dinosaurs examines those that possess a backward-pointing pubis bone.

More than 100 specimens are featured in the two dinosaur halls, representing roughly 5 percent of the Museum's collection of 2,000 dinosaur fossils. Interactive computer stations combine video, animation, and illustrations to examine the evolutionary relationships between dinosaurs and their habitats in different time periods.

With the renovation of these halls, some of the Museum's most famous dinosaurs have been remounted to reflect changes in the scientific understanding of what these animals were like. Tyrannosaurus rex, previously displayed upright with its tail resting on the ground according to older scientific thinking, was completely disassembled, cleaned, conserved, and repositioned in a sleek, stalking pose with its tail poised in the air and its head looming just above visitors. Apatosaurus—previously referred to as Brontosaurus—has a new skull, additional neck bones, and a tail that has been raised off the ground and lengthened by almost 20 feet.

Hall of Ornithischian Dinosaurs
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Also on display is one of the first dinosaur nests ever discovered, collected in 1923 in the Gobi of Mongolia by the legendary dinosaur hunter Roy Chapman Andrews. For 70 years, the eggs in this nest were thought to belong to Protoceratops, a plant-eating, horned dinosaur that was common where the nests were found. In 1993, Museum scientists found a meat-eating oviraptorid dinosaur embryo preserved inside the same type of egg, providing a completely new identity for the eggs discovered in 1923. A cast of the dinosaur embryo is on view along with the original dinosaur nest. This exhibit provides a vivid example of the surprises generated by ongoing scientific research and the difficulties of studying animals that died millions of years ago. Other highlights of the dinosaur halls include:

• The first Velociraptor skull ever found and two recently discovered embryonic-sized dinosaur skulls that may be baby Velociraptors
• The predatory Allosaurus, shown feeding on the partial carcass of an Apatosaurus. The bones of the Apatosaurus are marked with grooves that may have been caused by the teeth or claws of the 140-million-year-old predator; Allosaurus teeth found nearby inspired the idea for the mount.
• The only real fossils (as opposed to casts) of Deinonychus on view anywhere in the world. Studies of this dinosaur sparked the theory that dinosaurs were active, relatively intelligent animals. These studies also supported the emergence of the idea that modern birds are a type of living dinosaur.
• Stegosaurus, a 140-million-year-old dinosaur with distinctive rows of plates down the center of its back and large spikes on the end of its tail. Also on view is a cast of the first juvenile Stegosaurus ever found.
• The 65-million-year-old horned dinosaur Triceratops. This animal has a large frill on the back of its skull, as well as two large horns over its eyes and a smaller horn on the end of its nose. On the left side of this specimen's skull is a partly healed injury, possibly inflicted by another Triceratops.

Hall of Primitive Mammals
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Completing the story of vertebrate evolution, the Lila Acheson Wallace Wing of Mammals and Their Extinct Relatives consists of the Hall of Primitive Mammals and the Paul and Irma Milstein Hall of Advanced Mammals. These halls tell a fascinating tale of great diversification, sudden extinctions, and the forces that determine the success or obliteration of life, serving as both warning and inspiration. Mammals evolved at nearly the same time as the first dinosaurs, and the roots of the mammalian line reach back almost 300 million years. Some of the very early relatives of mammals, creatures resembling enormous lizards with giant fins along their backs, actually lived millions of years before the dinosaurs. Because dinosaurs and mammals are differentiated by a number of physical characteristics and are members of two separate evolutionary lineages, they are exhibited separately.

The Lila Acheson Wallace Wing of Mammals and Their Extinct Relatives showcases approximately 250 fossils representing about 0.1 percent of the Museum's complete collection of 250,000 fossil mammal specimens. Included are mastodons, saber-toothed cats, and giant sloths, with such highlights as:

• The mummified remains of a baby mammoth that lived 25,000 years ago, whose head, trunk, and leg were found "freeze-dried" in the Alaskan tundra
• A 12-million-year-old early horse called Protohippus, which may have died while trying to give birth (parts of a foal's skeleton are still clearly visible tucked behind the mother's pelvis)
• An early burrow-dwelling relative of the modern beaver, Palaeocastor, shown as it was found: at the bottom of an elaborate eight-foot-long spiral burrow called a "devil's corkscrew"
• Andrewsarchus, the largest land-dwelling carnivorous mammal known, which is displayed in the whale alcove because some evolutionary studies suggest that it is closely related to the modern whale

Hall of Advanced Mammals
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Three giant murals commissioned by the Museum from the artist Charles R. Knight in 1911 have been restored and returned to view for the first time since 1966. Knight was one of the first artists to re-create animals and environments of past eras based on careful study of the fossil record. In addition, dozens of smaller paintings by Knight are displayed throughout the fossil mammal halls, serving as evocative illustrations of extinct creatures in their natural habitats.

Related Exhibits

Two exhibits are on display in the corridor between the Hall of Vertebrate Origins and the Hall of Saurischian Dinosaurs. The first explores the history of paleontology at the Museum and includes the first dinosaur specimen collected by Museum researchers: the pelvis of a Diplodocus discovered in 1897. Video footage and archival photographs show visitors the Museum's fossil expeditions, from the first, in 1891, to those of the present day.

To illustrate the work involved in discovering, excavating, preparing, and studying fossils, a series of exhibits follows the story of the discovery of an Oviraptor dinosaur specimen. A re-creation of a Gobi fossil site, a preparation lab, and a cast of the specimen are accompanied by videos explaining the procedures that take place in the field and in the Museum. The Oviraptor, found during the Museum's 1994 expedition to the Gobi, died while nesting on its eggs, providing the first direct evidence of nesting behavior in dinosaurs.