Hi and welcome back to With Michelle! The Jurassic Park and Jurassic World franchise, is entirely fictional, so you don’t have to worry that dinosaurs are coming to get you. However, the story was in fact inspired by important changes in the scientific world. Over the course of the franchise, everything might not have been accurate, but the filmmakers have incorporated some expert advice on how to make the dinosaurs as realistic as possible.

Here’s how scientific discoveries really inspired the franchise. When Michael Crichton wrote the 1990 sci-fi novel that inspired the first Jurassic Park movie in 1993, he was inspired by paleontologist Jack Horner’s 1988 book Digging Dinosaurs, on dinosaur behavior and the discoveries made in the prior decades. “He bases the character of Dr. Alan Grant on a guy digging up baby dinosaurs in Montana at a place called Egg Hill.

What Jurassic Park Gets Right About Dinosaurs: Carrano gave Jurassic Park high marks for the basics of the dinosaurs that show up in the franchise. “The franchise gets one very important thing right: Dinosaurs were once active, living things that were as successful on land as any animal before or since,” he added.

What Jurassic Park Gets Wrong About Dinosaurs: Now while the franchise has helped spread the word on some truths about dinosaurs, it has also introduced new misconceptions. In particular, one question that paleontologists didn’t often have to field before Jurassic Park is whether dinosaur DNA exists and if dinosaurs can be cloned. “The oldest DNA that has been recovered from fossil record is well under a million years old, and these non-bird dinosaurs all died out 65 million years ago. Because [DNA] is a fragile molecule, it’s not thought to have survived as far back as the Jurassic period.” (Horner explains that, in 1993, when the first movie was made, scientists didn’t yet know that they wouldn’t be able to find dinosaur DNA, adding that he and a grad student tried.) The films tend to be off on the sizes of some dinosaurs, and filmmakers have invented new functions for some of their physical attributes.

The Velociraptor is one of the dinosaurs that the movie depicts as larger than it would have been in real life. (Carrano says it should be just about three feet tall.). Ankylosaurus is shown as having a club on it’s tail for self-defense, but that was probably for getting the female dinosaurs attention, says Horner, and the Mosasaurus in Jurassic World (2015) is depicted as about the size of a whale when it would have been half that length, according to Barta. The opposite is the case with the Dilophosaurus, “which would have been larger than it was portrayed in the movie. This depiction is the most inaccurate dinosaur in the movies,” says Barta. “We wouldn’t be able to have fossilized evidence of a poison gland or a bony structure near the throat for the support of anything like a frill. We have no evidence for either of those things in actual fossils.”

Those who find the Tyrannosaurus (or the T-Rex) terrifying will be relieved to know that it wouldn’t have able to run because it didn’t have large enough muscles, and that the dinosaurs probably sounded less scary as well. Scientists believe they grunted and hissed but probably didn’t really roar.