They're all dead.
Sure, there was that mass extinction 66 million years ago when a giant asteroid hit the earth, but not everything died. So, which dinosaurs are still alive? Birds! That’s right: birds are dinosaurs. One of several physical characteristics that help to classify a creature as a dinosaur is a hole at the hip socket (versus just a depression). Birds have this hole and a lineage that stretches all the way back to the Mesozoic Era. In fact, studies have revealed that Tyrannosaurus rex and birds are more closely related than either is to the alligator. Bone features tell us birds evolved from meat-eating dinosaurs (called theropods) such as the T. rex, and this has been confirmed from fossil protein sequences. Definitely dinosaurs!
If it ends in "-saurus," it's a dino.
“Saurus” comes from ancient Greek and means “lizard” (not dino). So, although Tyrannosaurus means “terrible lizard” and is a dinosaur, “phytosaur” means “plant lizard,” and it wasn’t a dinosaur or a crocodile (which it looked like) and didn’t even eat plants! A phytosaur is a reptile, which is the point in the family tree it shares with dinosaurs. Here’s what the lineage looks like:
Animalia → Vertebrata → Tetrapoda → Amniota → Reptila → Archosauria → Dinosauria
Each of these groups are nested within each other (think Russian dolls), so a dinosaur is also an archosaur, an archosaur is also a reptile, and so on. Therefore, dinosaurs are really a sub-grouping of reptiles. But that doesn’t mean they look like today’s typical reptile, which brings us to…
All dinosaurs had scales.
Actually, paleontologists now think that many dinosaurs had some form of feathery covering! Skin impressions of dinosaurs and carbonized remains of feathers have shed much more light on what their external coverings looked like, and they were more feathered or downy than we first thought. We now know that most meat-eating dinosaurs, and at least some herbivores, were adorned in this way.
All dinosaurs were big.
While some were the largest animals ever to have lived on land—we’re talking about you, long-necked, plant-eating sauropods—some were smaller than a housecat. And then there are the tiny living dinosaurs of today, such as hummingbirds. Dinosaurs came in all sizes.
Dinosaurs swam in the oceans and flew in the sky.
Nope. Dinosaurs from prehistoric times all lived predominantly on land, although the ones that evolved flight became birds. But when we think of the big pterosaurs (“pterodactyls”) flying during the Age of Dinosaurs, these were not dinosaurs but a different archosaurian reptile. Likewise, ichthyosaurs, plesiosaurs, mosasaurs, and marine reptiles of that age were not dinosaurs, either. So in other words, not all prehistoric animals were dinosaurs.
—Randy Irmis, Ph.D., is the paleontology curator and Michael Mozdy MA’99 is a digital science writer for the Natural History Museum of Utah.