Rhynchosaurs were a group of reptiles that lived about 220 million years ago during the Triassic period. They're not considered dinosaurs, although neither are pterodactyls nor dimetrodons, although popular culture considers them to be such.
My readings recently in a book about dinosaurs has often mentioned the other non-dinosaurs with whom they lived, which is pretty cool to me.
These triassic reptiles are considered to be archosauromorphs, a group ancestral to both crocodilians and dinosaurs. The archosaurs and archosauromorphs are generally crocodile-like, although some such as the rhynchosaurs were plant-eaters.
In this case, the rhynchosaurs are at least "distant cousins" to the dinosaurs. Other prehistoric fauna, such as giant amphibians and therapsids (mammal-like lizards who ruled the Earth before dinosaurs), are not really part of the extended dinosaur relations.
Doing a casual search on Google, I discovered a rather unexpected connection with Dungens and Dragons.