Callovosaurus was a small, primitive iguanodontid (or, as some research suggests, possibly a dryosaurid) dinosaur that lived in Europe during the Late Jurassic period, around 145 million years ago. Callovosaurus, due to its long face, might have been the first ancestor of the iguanodontids.
More real-life information: Callovosaurus at Wikipedia.
Jurassic Park (novel)
Callovosaurus' name accidentally replaced that of Microceratops in some editions of the Jurassic Park novel. So, Callovosaurus does not canonically appear in the Jurassic Park universe, not in the novels nor the films.