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

The Lower Jurassic Ichthyosaurus bones shown in the picture were found on the beach in Somerset, England. A minor fault ran through the skeleton and the rest was never found.

Ichthyosaurus bones from the Lower Jurassic, found on a beach in Somerset