Still, Spielberg insisted on using dramatic license when it came to some of his prehistoric stars’ appearances. Take, for example, those T. rex teeth. Bakker sent over diagrams of the chompers—which, in reality, were banana-shaped— but "the powers that be didn't like the real tooth shape," Bakker told Popular Mechanics. "The CGI rex and the robot had their fangs sharpened."
The most famous example is probably Spielberg's Velociraptor, which more closely resembles the Deinonychus. A major source for Crichton’s book was Gregory Paul’s Predatory Dinosaurs of the World, which labeled the Velociraptor as a Deinonychus subspecies; real Velociraptorsweighed less than 50 pounds and had feathers.
But in a bit of good fortune, a new, much bigger species called the Utahraptor was discovered during Jurassic Park’s production. In the forward of Raptor Red, Bakker wrote about a call from Dr. James Kirkland, who was part of the team that discovered Utahraptor:
"Jim!" I yelled. "You just found the giant raptor Spielberg made up for his movie." Jim thought I was daft. He didn't know about the other phone call I had gotten about giant raptors that morning. It was from one of the special effects artists in the Jurassic Park skunkworks ... the artists were suffering anxiety about what was to become the star of the movie—a raptor species that had never been documented by a real fossil. ... Just before Jim called, I'd listened to one artist complain that Spielberg had invented a raptor that didn't exist. ... He wanted hard facts, fossil data. "Yeah, a giant raptor's possible—theoretically. But you don't have any bones." But now Jim's Utahraptor gave him bones.
That dinosaur, discovered in January 1992, was almost exactly the same size as Jurassic Park's big female.