“For example, the three groups of animals at the top caecillians, salamanders and frogs all belong to the group amphibia, and all the groups of animals from junction [B] onwards are grouped as amniota.
The construction of such a diagram depends on the common ancestors that groups of animals share. For example, junction [A] represents the common ancestor between us and an echidna. Humans are part of eutheria and echidnas are monotremes. All animals sharing this common ancestor are labelled as mammals. Also, in evolutionary terms, we would say that two species that share a common ancestor at junction [A] would be more closely related than those species sharing a common ancestor at junction [B].
All pretty straightforward – but, this is where the reptile label runs into a problem.
I have circled the group of animals we normally refer to as reptiles. If you trace their paths back, you will arrive at junction [C], the last common ancestor of those groups. So, if we are to consider all animals from junction [C] onwards as reptiles, then we must also label birds as reptiles. We could do this I guess, but it would be redundant. The group of animals from junction [C] onwards are already referred to as sauropsida.
Hence, reptile is dead. I suspect Nietzsche will still be quoted more.”

via There’s No Such Thing As Reptiles Any More – And Here’s Why | IFLScience.