I am trying to find the title of a book where siblings have two halves of this pyramid thingy, put them together, and get stuck in a pocket out of time with dinosaurs and a few thousand people who are stuck there too. I listened to the book a few years ago when I was 6-7 and it scared me a lot so my mom got rid of it. I now think it would be worth a read. Any ideas? I may have gotten a few bits of it wrong.
Could it be Footprints of Thunder by James F. David?
The summary mentions time displacement, but no "pyramid thingy".
When the boundaries between past and present dissolve, flooding the earth with dinosaurs and turning cities into primeval forests, an increasingly unstable American president searches desperately for a solution to the imminent apocalypse.
A quick dive into the Google Books excerpts shows that two of the main characters are Chris and Rosa, a pair of stepsiblings from a blended family.
I don't know if this is the book you read but I pretty sure it's the one I read, especially after seeing the alternate cover.