Joel Sartore is a modern-day Noah, building a portrait collection of endangered and at risk animals instead of an ark. The goal of the Photo Ark is to document biodiversity, show what's at stake, and to get people to care while there's still time. More than 3,000 species have been photographed to date, with more to come. Endangered: Photo Ark features our editor's favorite photographs from Sartores captivating collection.