Personally, I think the first one had much more of an interesting and fun storyline than the second one. The second seemed rather, well, EMPTY.
And indeed, what IS a dinosaur doing in a movie (even a CG movie) about the latter half of the Pleistocene ice age?

Dinosaurs were
long-since extinct by then.
(Unless they're gonna play on some "frozen T-Rex thawed out by the warming trend seen in Ice Age 2" type thing. lol)
Was thinking this too.
It's just a movie for fun though. I'm a dino kinda girl and love Ice Age so regardless of how unaccurate this might be,I wanna see it. Maybe the t-rex was in a ice block and it melted or something. I dunno. We shall find out,huh?