Final answer:
Crocodiles are part of the archosaur group, which also includes alligators, birds, and various extinct reptiles such as dinosaurs and pterosaurs. They belong to the Crocodilia order and are closely related to birds, differing from lizards, snakes, and tuataras which are part of the Lepidosauromorpha group.
Step-by-step explanation:
The answer to the question of which one of the following is an archosaur group is a. Crocodiles. The diapsids diverged into two groups, the Archosauromorpha and the Lepidosauromorpha during the Mesozoic period. The archosaurs include modern crocodiles and alligators, and the extinct ichthyosaurs, pterosaurs, dinosaurs, and birds.
Specifically, crocodiles belong to the order Crocodilia, which makes them and alligators the closest living relatives of birds, and both are part of the archosaur group. This distinguishes them from lizards, snakes, and tuataras, which are part of the Lepidosauromorpha group, specifically the order Squamata.