Nagas are taurs: A proof.

Snakes are not all tail. They are all torso with a little bit of tail.

A snake's tail starts where the cloaca is located, typically a few to a few ten cm from the tail tip depending on snake length. All the organs are packed into the rest of the body between the neck and cloaca.

Therefore, the serpentine mass below a naga's hips is not their tail, but rather a second torso.

Nagas have a humanoid torso and a non-humanoid torso.

Therefore, nagas are taurs.

Q.E.D.