I can't remember where, but I know this got covered somewhere. If I remember right, you won't have a round to react unless you're falling from a height greater than over 600 feet, or something along those lines?
In any case, you might want to consider a Snapleaf, in order to get Feather Fall off as an immediate action.
That little item has saved two of my PC's lives at different times.
Ring of feather falling might be useful in this situation.
Or boots of the cat for cheaper and a less contested slot.
I think snap leaf is a one time use. A ring of feather fall is probably your best bet, and it's crazy cheap.
Ummm...unless I'm missing something you're a 7th level character and the DC to stay in the saddle of your mount is a flat 5, near as I can tell by the ride skill description.
You're probably wearing a breastplate that has a -4 armor check penalty. If you purchase a military saddle for your pteranodon you get a +2 to stay in the saddle. If you also have 7 ranks in ride and at least not a dex penalty you'll have a +5 ride check. Meaning you can't fail.
Though the ride check can be easily beaten, falling unconscious can turn into a death sentence without some falling backup. I'd recommend protections that don't require actions on your part.