Claws for climbing
That Archaeopteryx almost definitely used its claws on the front wings to climb is clearly paralleled by the Hoatzin (Opisthocomus) a heavily built bird occurring in South America and belonging to the cuckoo family. Its young possess conspicuous claws on the digits of the wings with which it is able to climb away from possible predators. These claws are usually considered to be a secondary development, however, their resemblance to the claws of the Archaeopteryx is remarkable. When the Hoatzin chicks grow up they lose these claws, but the adult birds are nevertheless poor fliers.
Species: Opisthocomus hoazin