Dinosaur comes from the Greek terms dienos (terrible) and sauros (lizard). Dinosaurs are their own category of animal, most closely related to birds and crocodiles. They come from a group of reptiles called Archosauromorphs. Lizards come from a distantly related reptile group called Lepidosauromorphs.
![Dinosaur comes from the Greek terms dienos (terrible) and sauros (lizard). Dinosaurs are their own Dinosaur comes from the Greek terms dienos (terrible) and sauros (lizard). Dinosaurs are their own](https://media.proprofs.com/images/discuss/user_images/153336/80319108223.jpg)
Dinosaurs (including birds) are, however, related to crocodiles. Now, lizards, dinosaurs, and crocodiles are all reptiles. (Yes, that does mean that, in terms of phylogenetics, birds are reptiles - no question about it). Reptiles (diapsids) split from mammals (synapsids) before dinosaurs and mammals proper even evolved.
There are two major groups of archosaurs; the bird line archosaurs, and the crocodile line archosaurs. Bird line includes birds, their extinct relatives and ancestors, dinosaurs, the closest relatives of those animals, silesaurs, and a related group, pterosaurs.