Question

in older classification schemes, the group called reptilia was defined as consisting of lizards, turtles, and snakes. birds were separated into the group called aves. why is aves not a clade?
lizards and birds are more closely related than are turtles and birds.
it does not include the reptiles.
birds are warm blooded, and snakes are cold blooded.
some extinct reptiles could fly

Explanation:

A clade is a monophyletic group that includes a common ancestor and all its descendants. In older classifications, Aves (birds) is separated from Reptilia, but birds share a more recent common ancestor with lizards, turtles, and snakes than these reptiles do with each other. Excluding the reptile group (the closest relatives of birds) means Aves does not include all descendants of its common ancestor, so it is not a clade.

Answer:

It does not include the reptiles.