How are reptiles alike?

traditionally, a reptile is any amniote who belongs to the reptilia. they're generally defined as being "a group of tetrapods with an ectothermic ('cold-blooded') metabolism and amniotic development". however, dinosaurs, and therefore birds, do not fit all of these requirements, and birds are currently excluded from the traditional classification of a reptile. birds are dinosaurs, and as such, cladistically (the type of classifying organisms based on evolutionary relationships), are reptiles. reptiles are members of the group sauropsida, which includes all reptiles and their closest (now extinct) non-reptilian relatives.