Evolution..Traits never appear, disappear and then reappear. WHY?

My professor had this interesting discussion.. what is your opinion?   


Current evolutionary theory holds that the most recent ancestor of birds are dinosuars. This result completely changes the way we think about dinosaurs.

Dinosaurs are not extinct. They are in the trees! The fact that birds have feathers and most dinosaurs do not is trivial. Why do we bother with this? The fact that birds exhibit a great deal of parental care may imply that dinosaurs did the same - a very unreptile characteristic.

Crocodiles also exhibit a good deal of parental care, and they are behind the dinosaurs who are in front of the birds. Since crocodiles and birds exhibit parental care for their young, it follows that dinosaurs probably did too.

In evolution, traits appear and then disappear, but they never appear, disappear and then reappear. Explain why that is reasonable or unreasonable to you! Is it important for us?