According to the Russian linguist M.S. Andronov, Proto-Dravidian gave rise to 21 Dravidian Languages. They can be broadly classified into three groups: Northern group, Central group, and Southern group of Dravidian languages.
The Northern group consists of three languages. The central group consists ten langauages. Out of these ten, only telugu became a civilized language and the rest of the nine languages remained tribal languages. The southern group consists of languages which includes Kannada, Tamil, Malayalam, Tulu and others.
Telugu split from Proto-Dravidian between 1500-1000 BC. So, Telugu became a distinct language by the time any literary activity began to appear in the Tamil land.
Kannada split from Proto-Dravidian around 0 BC. Note that the current similarity in scripts between Kannada and Telugu has a lot more with Chalukyas rule of Andhra than the similarity between the languages. Admittedly, Kannada is Telugu's closest cousin. In India the history of scripts has been almost independent of the history of languages.
Proto-Dravidian gave rise to totally 21 Dravidian languages. They are
* Northern Group
* Central Group
* Southern Group
The other languages in the Central group provide invaluble information in deducing the prehistory of Telugu.
Gonds and Koyas(speaking Konda language) are closely related tribes. Gonds have an interesting story about the origin of their tribe. It also matches the story Koyas have to say about their origin. Once upon a time there were 1600 crores of Koyas at Dhavalagiri. They were very dirty and never used to take bath. Mahadeva got disgusted at their dirtiness and jailed them in a cave. However Parvati was very fond of them. She did penance and got a son called Lingo. Linga prayed Mahadeva that Koyas should be released. Shiva would release them on the condition that Lingo performs all the adventures that Shiva asks. Once Lingo performed all of them successfully, Shiva had to release them.
Lingo went away on a journey with all 1600 crores of them. On the way they crossed a river. Lingo gave them rice and "Jonna Pindi". There Koyas stole ghee of Aryan deities. By then there were already four groups among them called Taekam, Maarkam, Poosam, and telingam. Lingo built a town for them and divided them into castes.
There is a possibility that the words 'telingam' and telugu come from the same source.