This is a fossil ammonite (~3cm in diameter) from the Upper Jurassic, about 160-145 million years old. I haven't seen the movie yet, but I'm hoping against hope it features some ammonites. Though not dinosaurs, they are an important extinct group of cephalopods (the living nautilus is in a separate family of cephalopods) that went out with the dinosaurs at the Cretaceous/Tertiary extinction event. This ammonite has a nice pearly shell.
John Christensen