Fossils of dinosaurs, mammoths, and saber-toothed cats on display on the Museum's fourth floor are impressive and imposing specimens of animals that once roamed the Earth, then vanished during mass extinctions at the end of the Cretaceous and Pleistocene eras. Elsewhere in the Museum, visitors can see species whose more recent extinctions were caused by human activity, from the Dodo in the Hall of Biodiversity to the Passenger Pigeon, one of North America's most plentiful birds until the early 1900s, featured in the Hall of New York City Birds.

In the not-too-distant future, scientists expect that technological breakthroughs—and availability of genetic data from specimens of extinct species—will provide ways to revive vanished species. In this video, Museum Curator Ross MacPhee discusses the science and ethical considerations of "de-extinction."