1) They came up with the paNN - the ancestor of the rAgA, and mentioned plenty of them way before the word 'rAgA' appeared in any Sanskrit text. Many of them are still around. Some of the names are still in use. They seem to have had 103 paNNs at one point.
2) They used graha bhedam on their paNNs. The big 6 rAgAs (shankarAbharaNam, tODi, kalyANi, naTabhairavi (i.e. bhairavi) and harikAmbhOji (i.e. kAmbhoji) all came from this effort. And probably so did mOhanam and probably its graha bhedams - the big 5 of mOhanam, madhyamAvati, hindOlam, shuddha sAvEri and shuddha dhanyAsi. The pentatonic scales came first - and so mOhanam is probably the oldest rAgA of them all (after the Rig Veda and the unnamed rEvati of course).
3) They must have found the 22 srutis in their own way as it seems to be mentioned in one article and it is a natural consequence of graha bhEdam. This needs confirmation. But as I already discussed this many times in Technical Discussions, it arises naturally from the math, and Dr. Oke simply rediscovered it. Long after the original concept of a shruti was forgotten, the idea still persisted in the relative pitches of notes and phrases (and still does even now).
This part goes all the way back to the Sumerians. I mean every civilization at one point figured this out, but no one except the Indians put it all together like this.
4) But they were the first to figure out that the swaras could be reduced to 12 semi tones in an octave that we use now. Again this is a global phenomenon, because that's what will happen when you start from first principles.
5) Music aside, tamizh compositions are the oldest we have in Carnatic Music apart from the Vedas and Puranas.
6) Other stuff, probably the name Carnatic itself has Sanskrit-Tamizh origins (kara-naadam anyone? That's another word for AUM)
A layman's glance seems to suggest to me that they were closer to the nATyashAstra tradition than I thought and preserved it for much longer, especially as North India became prone to invasions and empire changes. The South was comparatively much more stable. Probably a very uniform tradition of music ruled all over this land at one point.
Actually the tamizh pann isai is possibly even older than the Sanskrit works out there if the dates are right and combined with the Vedic traditions, could have been the basis for the classical music tradition across the whole country at one point.
Found these elaborate articles on paNNs :
https://en.wikipedia.org/wiki/Pann
https://tamizisai.weebly.com/about-pans.html
https://venkataramaniblog.wordpress.com ... /pannisai/
The point is, the next rAgA in the list is gambhira nATa - and yup, it's older than we all think, even if its current name and form is much more recent. So this was a prelude to gambhira nATa.
Hope others will share more info.