Wikibooks has a book on the topic of: Proto-Turkic
Proto-Turkic is the linguistic reconstruction of the common ancestor of the Turkic languages that was spoken by the Proto-Turks before their divergence into the various Turkic peoples. Proto-Turkic separated into Oghur (western) and Common Turkic (eastern) branches. Candidates for the proto-Turkic homeland range from western Central Asia to Manchuria,[4] with most scholars agreeing that it lay in the eastern part of the Central Asian steppe,[5] while one author has postulated that Proto-Turkic originated 2,500 years ago in East Asia.[6]
The oldest records of a Turkic language, the Old TurkicOrkhon inscriptions of the 7th century Göktürkkhaganate, already shows characteristics of Eastern Common Turkic. For a long time, the reconstruction of Proto-Turkic relied on comparisons of Old Turkic with early sources of the Western Common Turkic branches, such as Oghuz and Kypchak, as well as the Western Oghur proper (Bulgar, Chuvash, Khazar). Because early attestation of these non-easternmost languages is much more sparse, reconstruction of Proto-Turkic still rests fundamentally on the easternmost Old Turkic of the Göktürks, however it now also includes a more comprehensive analysis of all written and spoken forms of the language.[7]
The Proto-Turkic language shows evidence of influence from several neighboring language groups, including Eastern Iranian, Tocharian, and Old Chinese.[8]
^Robbeets, Martine; Savelyev, Alexander (21 December 2017). Language Dispersal Beyond Farming. John Benjamins Publishing Company. p. 127. ISBN978-90-272-6464-0. "It is generally agreed among historians and linguists that the starting point of the Turkic migrations was located in the eastern part of the Central Asian steppe (see, e.g., Golden 1992, Kljastornyj & Suktanov 2009; Menges 1995:55). Turkologists use various definitions for describing the Proto-Turkic homeland, but most indicate more or less the same region. While Janhunen (1996:26, 2015:293) locates the Proto-Turkic homeland fairly precisely in Eastern Mongolia, Rona-Tas (1998:88), in a rather general manner, places the last habitat of the Turkic speakers before the disintegration of the family "in west and central Siberia and in the region south of it." The latter localization overlaps in large part with that proposed by Tenisev et al. (2006), who associate the Proto-Turkic urheimat with the vast area stretching from the Ordos Desert in Inner Mongolia to the foothils of the Sayan-Altai mountains in Southern Siberia."