any of the group of extinct reptiles, usually large in size, that lived during the Mesozoic Era, roughly 250 to 65 million years ago, or more broadly, any of the reptiles or birds that lived during that era;
e.g. The book had a picture of a dinosaur on the cover.
(noun)
someone or something that has become outdated and obsolete due to not adapting to changes in the times and circumstances;
e.g. The original model of a typewriter may be considered a dinosaur compared to modern computers.