Believed to be the largest and one of the most complete Stegosaurus fossils ever discovered, the 150-million-year-old fossil known as Apex will be showcased at the American Museum of Natural History beginning Sunday, December 8. This remarkable specimen, standing 11.5 feet tall and measuring 27 feet long, is nearly 80 percent intact and will welcome visitors just inside the entrance to the Richard Gilder Center for Science, Education, and Innovation.