Before I get any farther, I wanted to voice my many current thoughts, theories, and questions.
I was super excited to get into this book and figure out the mystery of it, so I have been locked in on picking up every clue and fitting them all together. Is the "prehistoric killer" an actual, physical dinosaur, or something more paranormal? Was there Jurassic World levels of mutating and experimentation, or just a thought-to-be-extinct species not really being gone?
My first and most solid idea for what the heck is going on with the museum at this point in the book is ghosts. Based on the few strange encounters Simon has had, both in the museum and with other characters, that has become my forefront theory. The museum's wealthy benefactor Evie mentions that she speaks to spirits and that the museum is haunted, which could be a misdirect and her just being old and crazy, but with that conversation happening only a chapter after Simon's encounter with the "zombie" triceratops that doesn't exist (but who's extensive damage to the museum's insect and animal exhibit does), I like to think the book is deliberately planting those clues. But, I also feel like just explaining it as "ghosts" isn't the entire truth. The physical world is affected, even small things like the atmosphere emulating a prehistoric one by gaining hot, humid temperatures and an excess of oxygen. This makes me think the "hauntings" are more like memories, definitely still supernatural, but more like the past is imprinting on the present. Although, that sounds really metaphorical and complicated, so I guess they're just poltergeist dinosaurs, I don't know.
And all that is not even mentioning that I still have no idea what the deal with Morgan's disappearance is! All I have is that it's not just connected to the museum like I already knew from the blurb, but probably to the "ghost dinosaurs" too, seeing as Simon's mom mentions "evil, nasty lizards" as the ones who took Morgan and who are waiting to feast on Simon too. I find it interesting she seems to be haunted by similar things to Simon, and as far back as right after Morgan disappeared. I definitely think this situation is bigger than I know, involving Morgan and a lot more shady business from the many, maybe even the very first, executive director of the museum, but I can't say anything for certain.
Watch me speculate all this and then it turns out Simon was just genuinely going crazy. I still have so much of this book left, and I'm excited to find out if I'll be validated or completely blindsided by the truth.