Vertebrates: Reptiles

The term ‘reptile’, like ‘fish’, can be usefully applied to groups of animals today even if the way these words have been used has changed over time (see Vertebrates: Fish).

Living reptiles encompass a huge range of biodiversity which includes turtles, tuatara, lizards, snakes and crocodiles. These are all ectothermic animals (‘cold-blooded’) with skin covered in scales. Reptile biodiversity becomes even broader when we include extinct marine reptiles such as mosasaurs, plesiosaurs and ichthyosaurs. Living and extinct, these reptile groups are each the descendant of an ancestor with skin containing scales made from keratin (the material our hair and nails is constructed from), having hatched from an egg with a protective outer shell, and possessing a skull with two open spaces on both the left and right sides used for muscle attachment. The challenge here is that dinosaurs are descendants of that same ancestor, and birds are descendants of dinosaurs. The term ‘reptile’ becomes less useful for describing a scaly ectotherm when we need to also include birds in that same definition. This section features the diapsid and anapsid amniotes that are not dinosaurs: here we refer to those animals as ‘reptiles’, and save birds for their own section.