Marty Guitierrez was a field biologist from Yale. He was sent samples from the bites Tina Bowman sustained from an unknown lizard species. Originally, he believed they were caused by a species of Basilisk lizard. Even though he had seen her drawing, Guitierrez identified the animal as such because he believed her depiction to have been exaggerated.
However, he later believed it may be a new species after talking with Tina and learning of the peculiar gait of this ‘lizard’. He promptly checked a medical database and could find no records of hospitalization for Lizard bites. However, he found that the same lizards were biting infants in Costa Rican villages. This led him to believe that it may be a newly discovered species, whose behavior was being changed artificially through loss of its habitat. He feared that this habitat loss had changed the behavior of the ‘lizard’. Most specifically, he was concerned about disease transmission from lizards to humans, because lizards were known vectors for Central Saurian Encephalitis, which caused sleeping sickness in humans and horses.
He was able to find a specimen of this lizard, taking it from a howler monkey. The specimen turned out to be a Procompsognathus. Later he talked to Alan Grant, after the Nublar incident, to inform him of Grant’s current situation and inform him of a rumor of unknown animals migrating through Costa Rica. Years later, he took Richard Levine to a deserted beach to show him a washed up specimen of reptile. The specimen was destroyed, much to Levine’s dismay, and Guitierrez informed Levine of the fear of disease with the appearance of dead specimens of unknown animals.