Dinosaurs are relatives to birds.
Archosaurs are a group of diapsid amniotes whose living representatives consist of birds and crocodilians . Dinosaur . Throughout the remainder of this article , the term `` dinosaur '' is sometimes used generically to refer to the combined group of avian dinosaurs ( birds ) and non-avian dinosaurs ; at other times it is used to refer to the non-avian dinosaurs specifically , while the avian dinosaurs are sometimes simply referred to as `` birds '' . Dinosaurs are represented on every continent by both extant species ( birds ) and fossil remains . While the dinosaurs ' modern-day surviving avian lineage ( birds ) are generally small due to the constraints of flight , many prehistoric dinosaurs ( non-avian and avian ) were large-bodied -- the largest sauropod dinosaurs are estimated to have reached lengths of 39.7 m and heights of 18 m and were the largest land animals of all time .