According to the tradition initiated by Adi Shankara, this matha is in charge of the Atharvaveda.
Ushanas is the name of a Vedic rishi with the patronymic Kāvya (descendant of Kavi, AVŚ 4.29.6), who was later identified as Ushanas Shukra.
He gives 150 BCE (Patañjali) as a terminus ante quem for all Vedic Sanskrit literature, and 1200 BCE (the early Iron Age) as terminus post quem for the Atharvaveda.