You wanna know one of the biggest reason that mammals are special? We chew.
More on this here.
In fact, only mammals chew. (Pretty much. It's hard to make absolute statements in biology.)
The gist: We mammals have evolved warm bloodedness because it helps us move quickly and with sustained energy (reptiles have to bask in the sun, etc. to get warm). Hot bodies are costly, though--they burn something like 10 times more energy than being cold blooded. Not only do warm blooded animals have to eat way more (big snakes can go months without eating--try that sometime!), but we have to get every possible calorie out of the food we eat--and fast! Thus, we chew. So, what does it take to chew? Proper teeth, of course. And...the ability to breath and chew. Not choking to death is nice, too.
Therefore, the palate was born. The palate is the bone/flesh separating you nasal passage from your mouth. I never would have realized this, other than through reading about evolution, but other critters like birds and most reptiles (with the exception of crocodilians who hold their food underwater to drown it without, hopefully, drowning themselves) don't have palates. They breath through their mouth.
Birdy mouth nasal passages entering mouth (it's the thin slits in the middle of the roof of the mouth):
|Dinos were mostly mouth breathers.|
http://faculty.plattsburgh.edu/thomas.wolosz/turbinates.htm (And images below.)
|Not Mouth Breather|
|Also Not (they're exceptions to the rule)|