J Bor writes that it has already been described by Somanatha .
It is probably this musicologist :
" Raga-vibodha of Somanatha (1610 CE ) is an important text in many ways. It is also an interesting link between the Karnataka Sangita of the South and Hindustani Music of the North. " (
https://sreenivasaraos.com/ )
So , that would make Chhayanat relatively old .
Btw , looking for old jod-ragas I found that Gaud Malhar has already been mentioned in1575 .
Often sung :
_ " Eri Malaniya Gundh Lao Ri " - High Sa is among the first notes .
_ "Jhanana jhanana jhana .... baaje biChuvaa "
https://www.youtube.com/watch?v=JuG7NLLCmos
Some rhythmic displacements by Pt Shubhada Paradkar
https://www.youtube.com/watch?v=OQnI_SWwHak
Ud Rashid Khan - also some layakari
https://www.youtube.com/watch?v=jjLe9RI2NKM
Pt Jasraj - some syncopations
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