Really the best way to understand anything about dinosaurs is by looking at living animals. You look at birds and then look at the closest living anc… - Mark Norell

If you look at crocodiles today, they aren’t really representative of what the lineage of crocodiles look like. Crocodiles are represented by about 23 species, plus or minus a couple. Along that lineage the more primitive members weren’t aquatic. A lot of them were bipedal, a lot of them looked like little dinosaurs. Some were armored, others had no teeth. They were all fully terrestrial. So this is just the last vestige of that radiation that we’re seeing. And the ancestor of both dinosaurs and crocodiles would have, to the untrained eye, looked much more like a dinosaur.

If you saw a baby tyrannosaur you would probably think it was a weird looking bird. A full grown one might have had feathers too, maybe not on its whole body though, maybe more of an ornamental display sort of feathers. So traits in the theropod dinosaurs were more birdlike than say, crocodiles.

A couple things that we do know about theropods—the ones that most closely related to birds—is that they brooded their nests. If you go deeper in the tree, what you see is that for sauropods, we have no direct evidence that they returned to the nest after the eggs were laid. Most of the evidence for that comes from an excavation in Argentina called Auca Mahuevo. What’s thought with sauropods is that they’d just lay a bunch of eggs and leave them alone—the turtle model. Few of those would ever reach adulthood.