Chuvash language
Later Turkic peoples in Mongolia all spoke forms of Common Turkic (z-Turkic) as opposed to Oghur (Bulgharic) Turkic, which withdrew to the west in the 4th century. The Chuvash language, spoken by 1 million people in European Russia, is the only living representative of Oghur Turkic which split from Proto Turkic around the 1st century AD.