subdivision between Pre-Proto-Basque and Old Proto-Basque.

According to linguist José Ignacio Hualde, since Aquitanian was spoken over a vast area (some names of Aquitanian origin have been found as far south as Soria in Castile), it likely featured several dialects. He suggests that Basque may have evolved from one of these dialects, though it remains unclear which Aquitanian names belong to Basque's direct ancestor and which come from a related sister