Reptiles, which include dinosaurs in some classifications, have undifferentiated teeth and a different bone structure from mammals. They are cold blooded and usually lay eggs. The first reptiles appear in the Carboniferous period.

Crocodiles and similar reptiles are protected by hard, horny scales called scutes The picture shows the scutes on a fossilised section of crocodile skin. Crocodile scutes (or more precisely scutum singular, or scuta plural) are occasionally found in the Eocene London Clay strata of Kent, England.