Does the death of the dinosaurs line up with God's cursing them to crawl on their bellies at the Garden of Eden? Science is sometimes incorrect on timing and nobody actually knows when the world started but God himself. The Aramaic Bible online says in GEN 1:21 that he made them and we know they were here.
I'm not sure that I have ever heard the theory that the "serpent" in Genesis 3 was a dinosaur. The Hebrew word is the same one that is used in Exodus 4 and 7 for the beast which Moses' rod turned into. There is no reason to believe it was some sort of dinosaur rather than a snake.
What exactly happened to the dinosaurs we don't know. The Bible doesn't say. Presumably the land based ones had died out by the time of the flood; otherwise Noah would have preserved them on the ark. But at what point or why they became extinct, if indeed they did, is not said. Two theories that I have heard are that they never existed, but God just put the fossils in the rocks at creation to see if man would still acknowledge him in the face of that "evidence." The other is that dinosaurs, like lizards today, continued to grow all their lives. Just as man's life was shortened after the flood, so was theirs, and so we now have their descendants in smaller forms. Both of these theories have some serious problems, but are credible on their face. The Bible just doesn't say what happened to the dinosaurs.
Gen 1:21 may not mention the dinosaurs at all, other than that some of them could be included with the flying things and the beasts of the water.