Looking so different from chick to adult is a trait birds inherited from their ancestors, the non avian dinosaurs. Many dinosaurs that have been thought to be close relatives turned out to be the same species, but at a different age. So the number of species have now been cut down. Triceratops for example turned out to be a juvenile for of Torosaurus. Source: https://www.youtube.com/watch?v=kQa11RMCeSI
Looking so different from chick to adult is a trait birds inherited from their ancestors, the non avian dinosaurs. Many dinosaurs that have been thought to be close relatives turned out to be the same species, but at a different age. So the number of species have now been cut down. Triceratops for example turned out to be a juvenile for of Torosaurus. Source: https://www.youtube.com/watch?v=kQa11RMCeSI