Rodrigues (2007) considers the Proto-Tupian
linguistic homeland to be somewhere between the
Guaporé and
Aripuanã rivers, in the
Madeira River basin. Much of this area corresponds to the modern-day state of
Rondônia, Brazil. Five of the ten Tupian branches are found in this area, as well as some
Tupi–Guarani languages (especially
Kagwahiva), making it the probable linguistic homeland of these languages and maybe of the peoples that traditionally speak them. Rodrigues believes that Proto-Tupian dates back to around 5000
BP. O'Hagan (2014) proposes that Proto-Tupi-Guarani was spoken in the region of the lower
Tocantins and
Xingu Rivers. Proto-Omagua-Kokama then expanded up the
Amazon River, Proto-Tupinamba expanded south along the Atlantic coast, and the Southern branch expanded up along the Tocantins/
Araguaia River towards the
Paraná River basin. ==Phonology==