Mamenchisaurus is a genus of sauropod dinosaur known for their remarkably long necks which made up nearly half the total body length. Their shoulders were somewhat higher than the hips. The different species vary in length, from around 15 m to at least 26 m, and maybe up to 35 m. The species differ in overall size and specific features of the skull and skeleton, but share typical sauropod traits, like quadrupedalism, large bodies, small heads, and long tails.

Dryptosaurus is a genus of tyrannosauroid that lived approximately 67 million years ago during the late Cretaceous period in what is now New Jersey. Dryptosaurus was a large, bipedal, ground-dwelling carnivore, that grow up to 7.5 m long and weigh up to 1.5 t. Dryptosaurus seems to have had relatively long arms when compared with more derived tyrannosaurs. Its hands, which are also relatively large were believed to have had three fingers.

Nearly all dinosaurs discovered share certain modifications to the ancestral archosaurian skeleton, or are clearly descendants of older dinosaurs showing these modifications. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical for Dinosauria. The earliest dinosaurs had them and passed them on to their descendants.

One such notable trait shared by almost all dinosaurs is that the radius, a lower arm bone, is shorter than 80% of humerus length.

Dinosaurs are still alive today in the form of modern birds.

The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. The Archaeopteryx has famously been known as the first example of a bird for over a century, and this concept has been fine-tuned as better understanding of evolution has developed in recent decades.

Four distinct lineages of bird survived the Cretaceous–Paleogene extinction event 66 million years ago, giving rise to ostriches and relatives (Paleognathae), ducks and relatives (Anseriformes), ground-living fowl (Galliformes), and "modern birds" (Neoaves).

Phylogenetically, Aves is usually defined as all descendants of the most recent common ancestor of a specific modern bird species (such as the house sparrow, Passer domesticus), and either Archaeopteryx, or some prehistoric species closer to Neornithes. If the latter classification is used then the larger group is termed Avialae. Currently, the relationship between dinosaurs, Archaeopteryx, and modern birds is still under debate.

To differentiate, the dinosaurs that lived through the Mesozoic and ultimately went extinct during the Cretaceous–Paleogene extinction event 66 million years ago are now commonly known as "non-avian dinosaurs."