Dr. Marty Gutierrez is an American biologist who lives in Costa Rica. He plays an expository role in both novels. In the first novel, he identifies an unknown lizard that attacks a little girl as "Basiliscus amoratus". He is initially unhappy with this identification because the lizard was more venomous than expected and had three toes. He searches the beach where she was attacked and finds the corpse of a similar lizard in the mouth of a howler monkey, which he promptly sends for laboratory analysis. He also appears at the end of the novel, when the survivors are being held back for questioning by the Costa Rican government. He tells Dr. Grant that the survivors, with the exception of the children, will not be leaving any time soon.