A Timeline

1850s: Some scientists notice the connection between dinosaurs & birds and think birds might have evolved from dinosaurs, given similarity between Archaeopteryx and many dinosaurs, as well as between dinosaurs and living birds

1960s: Deinonychus is discovered. Scientists starting to realize birds did evolve from dinosaurs; other ideas become fringe hypotheses

1970s: More dinosaurs are discovered that point to dinosaur behavior being more like birds than reptiles

1980s: Scientists begin using evolutionary relationships (ie, cladistics) to classify life, rather than Linnean Taxonomy (Kingdom-Phylum-Class etc.), especially for extinct creatures, because it really doesn’t apply to extinct life like, at all. Coelophysis, an early dinosaur, is speculatively depicted with feathers. Some very bird-like dinosaurs are debated on whether they are birds or dinosaurs.

1993: Birds are straight-up called dinosaurs in the famous film “Jurassic Park,” which is one of the first pieces of media to depict dinosaurs as extremely birdlike; changes public perception of dinosaurs dramatically

1996: Sinosauropteryx, the first feathered non-avian dinosaur, is revealed to the public. Birds determined to have evolved from dinosaurs, full stop; BANDits (birds-are-not-dinosaurs scientists) now a backwards, on-par-with creationists group. Since we classify dinosaurs based on their evolutionary relationships, we start calling birds dinosaurs, because they evolved from dinosaurs.

1999: Sinornithosaurus, the first raptor (ie, cousin of Velociraptor) dinosaur found with feathers, is described. Many other feathered dinosaurs are described as well, from all over the group closely related to birds. The Walking With Dinosaurs landmark documentary series calls birds dinosaurs.

2000: Microraptor, a raptor dinosaur with full wings on its arms and legs, is described

2001: Velociraptor is given… “feathers” in Jurassic Park III. Velociraptor also portrayed as more bird-like than ever. When Dinosaurs Roamed America, another groundbreaking dinosaur documentary, shows all members of the group closely related to birds (except T. rex) with feathers, including Deinonychus, all over their bodies. Also calls birds dinosaurs.

2002: A specimen of Psittacosaurus, a dinosaur about as far away from birds as you can get, is described with quills on its tail very similar to feathers

2004: Dilong, a small relative of T. rex, is found with feathers and display structures like modern birds

2007: Many feathered dinosaurs are now known from the group most closely related to birds. A specimen of Velociraptor with feather attachment sites on the arms for wing feathers is now known. Velociraptor now known to be definitely, no question, feathered

2009: Tianyulong, another dinosaur from a group very far from birds, is found with fluffy quills covering all over its back

2012: Feathered dinosaurs now coming out many times a year. Yutyrannus, a large and closer relative to T. rex, found with shaggy feathers all over its body

2014: Kulindadromeus, another dinosaur from the group very far from birds, is named. It has fluffy covering like that of Sinosauropteryx all over its body, rather than quills. Feathers determined to be mostly likely ancestral to all dinosaurs and lost secondarily in larger species (especially if fluff known on closest relatives, pterosaurs, is also feathers - see below).

2015: Zhenyuanlong, a close relative of Velociraptor the same size as Velociraptor, is found with extremely large wings. Raptor dinosaurs inferred to have large wing feathers unless anatomy indicates otherwise (such as having short wings). Jurassic World comes out, making dinosaurs less bird-like than in the original Jurassic Park - with lizard-like tails and behavior, and no feathers at all. Essentially, a huge step backwards.

2018: Branched fluffy covering very similar to feathers described now on multiple pterosaurs, the group most closely related to dinosaurs (think Pterodactyls). Fluffy covering considered ancestral to all members of the Pterosaur-Dinosaur group, if not all animals more closely related to birds than to crocodilians.