As their name implies, the Pterodactyls are a breed of prehistoric reptile with expansive leathery wings and a sharp elongated beak. Although distantly related to dinosaurs, pterodactyls are actually part of a different group, the pterosaurs.
They are mentioned by Kristen Connolly - the actress who plays Dana Polk - during an interview. She revealed that two of them appear in a deleted scene where they chased her character through the Facility during the Purge.
Pterodactyls were a species of flying reptiles within the group Pterosauria that lived during the Mesozoic Era, becoming extinct 65 million years ago. Many fables depict large reptiles that surviving this extinction event. Such fictions are typically based on interpretations of regional folklore, alleged eyewitness sightings, legends, unverified and/or fabricated physical evidence (like footprints), and works of traditional art that supposedly depict extinct creatures. Famous examples are Journey to the Center of the Earth and Pterodactyl.