Velociraptors were human-sized, highly intelligent predators.

Michael Crichton met with John Ostrom several times while writing Jurassic Park. Ostrom, the Yale paleontologist who had described Deinonychus antirrhopus in his landmark 1969 monograph, was at the time one of the most celebrated figures in American paleontology, credited with helping launch the Dinosaur Renaissance through his demonstration that certain dinosaurs had been active animals with bird-like metabolisms. The creature he had described from Montana was a revelation: a bipedal predator roughly the size of a wolf, with a sickle-shaped retractile claw on its second toe that Ostrom argued was used to pin and disembowel prey. It was, in every sense Crichton needed, terrifying.

The novel was published in 1990. In it, Crichton called his predators Velociraptors. He later told Ostrom, with some embarrassment, that the name change was deliberate, Velociraptor simply sounded better, more dramatic, more threatening than Deinonychus. Crichton acknowledged that the fictional creatures were based on Deinonychus in almost every anatomical detail, and that only the name had been changed. When Steven Spielberg's film adaptation reached theaters in 1993, it reached audiences of tens of millions, cementing the Velociraptor as the defining predator of popular prehistory: intelligent, coordinated, roughly human-sized, capable of operating door handles.

The real Velociraptor mongoliensis was a different animal. Its actual size was approximately two feet tall at the hip and five to six feet long, roughly the dimensions of a large turkey, weighing somewhere between 15 and 30 kilograms. Its skull was long, low, and narrow. It was feathered, as quill knobs preserved on specimens from Mongolia's Djadochta Formation have confirmed. It was certainly fast and probably dangerous to small prey, but it was not capable of terrorizing a resort island. The creature that audiences saw in the film was closer in size to Utahraptor ostrommaysorum, a North American dromaeosaurid described the same year the film was released, which reached lengths of seventeen feet.

The actual Velociraptor mongoliensis was formally named from Mongolian desert material discovered by the American Museum of Natural History's Central Asiatic Expeditions. Henry Fairfield Osborn named it in 1924 from skulls and claws recovered in the Gobi Desert. For decades it remained a relatively obscure genus in the technical literature, distinguishable from North American dromaeosaurids by its flatter skull and certain differences in limb proportions. It was not famous outside specialist circles before Crichton's novel.

Ostrom, asked about the substitution in later interviews, expressed philosophical acceptance. He recognized that Crichton had used his Deinonychus research as the basis for the novel's predators and that the name change was a creative rather than scientific decision. He noted that the anatomical details most prominently borrowed, the sickle claw, the bipedal stance, the apparent agility, had all come from his 1969 monograph describing Deinonychus, an animal Crichton had chosen not to name.

The Jurassic Park Velociraptor became, in the years after the film's release, probably the most recognizable non-avian dinosaur after Tyrannosaurus rex. Museum gift shops sold toys in the film's dimensions. Children learned the name, the silhouette, and the associated mythology of intelligence and pack coordination. The real Velociraptor mongoliensis, turkey-sized, feathered, from the deserts of Mongolia, existed in technical papers and in the footnotes of popular articles patiently explaining what the film had gotten wrong. Thirty years on, those footnotes have not dislodged the image.