The Earliest Known Dino?

sciencehabit writes "A team of paleontologists thinks it may have identified the earliest known dinosaur — a creature no bigger than a Labrador retriever that lived about 243 million years ago. That's at least 10 million years earlier than the oldest known dinos and could change researchers' views of how they evolved. But some scientists, including the study's authors, caution that the fossils could instead represent a close dino relative."

Re:Birds and dinosaurs

[Sique]

"Reptiles" is a paraphyletic group, and is no longer used. The classification "reptile" has some serious problems, as for instance turtles branched early from the other reptiles, later the mammal-like reptiles, and then the other branches of reptiles radiated. So reptiles would cover a very incomplete tree where one early branch is missing (mammals) and one very late one (birds). Instead we are talking "amniotes", meaning animals whose early development involves the growing of an amnios, a pouch in which the embryo develops. The amniotes then branch into Anapsides (including turtles), Synapsides (mammals and their predecessors) and Diapsides (all other reptile-like animals including the birds).

Re:Birds and dinosaurs

[Sique]

Upon reading a little about those groups, I noticed that molecular analysis does suggest that even though turtles have no additional holes in their skulls (which would morphologically put them into the anapsid group), it seems that they are closer related to some diapsid groups, especially lepidosauridae (lizards, snakes etc.pp.). So the point in time when the last common ancestor of turtles and other reptiles lived, is still debated.
So the question for this reconstructed animal is not so much if it fits a morphological definition of a dinosaur, but rather if the last common ancestor of this animal and a bird was living later than the last common ancestor of birds and crocodiles. If yes, then it would put it definitely into dinosaur territory, being either an early dinosaur or a member of one of the sister groups of early dinosaurs. If no, it might still be an archosaur, closer related to recent birds and crocodiles than to other lizards and snakes.