1.NounThose animals of the clade Dinosauria that existed during the Triassic, Jurassic and Cretaceous periods and are now extinct; that is, any member of the clade Dinosauria other than birds. .mw-parser-output .defdate{font-size:smaller}
"Despite what some cartoons portray, no humans were around when dinosaurs roamed the Earth."
2.NounAny of the animals belonging to the clade Dinosauria, including all non-avian dinosaurs (all extinct) and all birds (extant or extinct).
"Many people love their backyard birds, but some of us may not realize that those feathery friends are also literally dinosaurs, in a biologically accurate sense of that word."
3.NounAny extinct reptile, not necessarily belonging to Dinosauria, that existed between about 230 million and 65 million years ago, as well as the stem-mammal Dimetrodon.
"Pterosaurs, plesiosaurs, icthyosaurs — I don't know, they're all dinosaurs to me!"
4.NounSomeone or something that is very old or old-fashioned, especially someone who is not willing to change and adapt.
"She may be a tough old bird, but it's a mistake to write her off as a dinosaur; you do so at your own risk."
5.NounAnything no longer in common use or practice.
"I couldn't believe it when I saw the equipment that they were still using. Those machines were all dinosaurs, but they were busily cranking out production."