Other mistake: Just after the valley floods, Manny is seen pushing a log to pry the rock out blocking Ellie's way out. You can notice that Manny is pushing it the wrong way. (01:08:40)
Other mistake: During Scrat's encounter with the rotating ice slab, he jumps three times in the middle of the slab and falls through. He should have jumped on either end of the slab. Also, he fell through the ice standing up, and in the next shot he is upside down, pushing up on the ice slab.
Other mistake: Watching the green fish monster closing up to Sid and Diego, viewing the monster from underneath it, it would have taken approximately only one second for it to have reached them in the rate it was displayed traveling at (considering as of the end of that shot). But it only reaches them about eleven seconds later. (00:31:05)
Other mistake: After the "boat" is released from the rock, it glides past the nest where Scrat was before, yet the waves created by the massive "boat" would capsize the nest. The "boat" moves by without creating any wave.
Answer: Cretaceous, the purplish creature, is an Ichthyosaur. Maelstrom, the greenish creature, is a Pliosaur.
Bishop73