Proto-Tocharian, also spelled Proto-Tokharian (/təˈkɛəriən/ or /təˈkɑːriən/), is the reconstructed proto-language of the extinct Tocharian branch of the Indo-European languages. Proto-Tocharian is the unattested reconstructed ancestor of an Indo-European eponymous extinct branch, known from manuscripts dating from the 5th to the 8th century AD, which were on the northern edge of the Tarim Basin and the Lop Desert. The discovery of this language family in the early 20th century contradicted the formerly prevalent idea of an east–west division of the Indo-European language family on the centum–satem isogloss, and prompted reinvigorated study of the family.