Eodromaeus or Dawn Runner, is the ancestor of the predatory dinosaurs, including T-Rex. He is also the precursor ancestor to the birds.
“...On page 206 of this week’s issue of Science, a team working in Argentina reports the discovery of a very early dinosaur—possibly a distant ancestor of Tyrannosaurus rex—that lived about 230 million years ago, during what paleontologists call the dawn of the dinosaurs. The researchers say the new finds—two specimens that together make up a nearly complete skeleton of a diminutive, 1-meter-long dinosaur—and neighboring fossils show that dinosaurs didn’t outcompete other reptiles, but rather gradually replaced them as their predecessors died out for other reasons. More controversially, the team says the fossils show that one of the most well-known early dinosaurs, Eoraptor, long considered an ancestor of meat eaters like T. rex, was actually an ancestor of gigantic plant-eating dinosaurs like Apatosaurus….”