One of the premier attractions in New York City is the Museum's series of fossil halls, including its two famed dinosaur halls. The Museum is home to the world's largest collection of vertebrate fossils, totaling nearly one million specimens. More than 600 of these specimens, nearly 85 percent of which are real fossils as opposed to casts, are on view. Completely renovated between 1994 and 1996, the fossil halls now stand as a continuous loop on the fourth floor, telling the story of vertebrate evolution. Unlike most fossil exhibits, which are arranged in chronological order, the Museum's fossil halls display the specimens according to evolutionary relationships, dramatically illustrating the complex branches of the tree of life, in which animals are grouped according to their shared physical characteristics. Such relationships are determined through a method of scientific analysis called cladistics, which the Museum helped pioneer. The halls' renovation also allowed for new scientific interpretations of favorite displays, as well as the restoration of the fourth floor to its original architectural grandeur.