1 a) I thought I estsblished I already know about Pangaea
1) 10 degrees C? That translates to 50 degrees fahrenheit. I find that somewhat farfetch'd, but nevertheless, winter in antarctica would've been the reptilian equivalent of "rocks fall everybody dies"
2) First there was bacteria, then fish, then amphibians, then reptiles, then mammals/birds. There is an evolutionary order. It's just that fossil evidence links Dinosaurs to birds. There's even theories (which I believe in) that dinosaurs were warm-blooded.
edit: Hibernation eh? If everything was +50 degrees warmer than usual, that could work.