Troodon (/ˈtroʊ.ədɒn/ TROH-ə-don; Troödon in older sources) is a genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Cretaceous period (about 77 mya), though possible additional species are known from later in the Campanian and also from the early (and probably late) Maastrichtian age. It includes at least one species, Troodon formosus, though many fossils, possibly representing several species have been classified in this genus. These species ranged widely, with fossil remains recovered from as far north as Alaska and as far south as Wyoming and even possibly Texas and New Mexico. Discovered in 1855, T. formosus was among the first dinosaurs found in North America.