I read a theory that all the dinosaurs were carried on the ark, with all the other animals, when they were young, and thus small in size, allowing them to fit inside. But the fact that all, except possibly the crocodile, are now extinct, means this is unlikely (a disease that only effects dinosaurs? Maybe, but unlikely).
The other theory I’ve heard, is yours – that they were genetically changed animals produced by the Nephilim, when they inhabited the Earth.
I’ve come across a few issues. In Job 40:15-24 God tells Job that He created the behemoth, a dinosaur, which sounds like an Apatosaurus. In Job 41 God tells him about the Leviathan, which in Psalm 104:26 is also said to be created by God.
These verses say God created at least one type of dinosaur, and one, as yet unseen, sea monster. How do you think this fits? Did God create the dinosaurs, and then wipe them out exclusively? Did the Nephilm tamper with a few of them? Or is there a third answer?
I also reject the notion that because of their size, God told Noah to put only baby dinosaurs on the Ark. It’s pure speculation. But we’re not told specifically about the dinosaurs so anything we say is speculation.
The word behemoth in Job 40:15 comes from a root meaning beast. Scholars are far from united as to what Job meant. Speculation ranges all the way from dinosaur to mammoth to hippopotamus.
Leviathan (Job 41:1) is the same. It means “large aquatic animal” and has been translated as sea monster. None of these references require a dinosaur to fit the context of the passage. If we weren’t already looking for dinosaurs, I don’t believe we would have seen them in these passages.
I’ll stick with my view that dinosaurs were the product of genetic tinkering by Satan and the Nephilim in the pre-flood era and were destroyed along with the rest of creation in the flood.