Which of the following characteristics are typical of reptiles?

Reptiles are characterized by having keratinized, waterproof scales, which enable them to conserve water in terrestrial environments. These scales are an adaptation that protects them from desiccation (drying out) and allows them to thrive in various habitats, including deserts and dry forests. The presence of keratin, a tough protein, helps provide a barrier against physical injury and environmental factors.

Other characteristics that do not apply to reptiles include the presence of feathers, which are specific to birds and indicate a different evolutionary lineage. Moist skin is more commonly found in amphibians, which rely on their skin for moisture absorption and cutaneous respiration. Gills are typical of aquatic organisms, such as fish, and are not found in reptiles, which breathe using lungs. Thus, keratinized, waterproof scales uniquely define the reptilian class among these options.