ProtoSiva Seals of Harappa and Mohenjo-daro . The Harappan Civilization is said to have flourished c. 2500-1900 BC Deciphering the Indus Script
Of course others argue that the seals don't represent Shiva or Yogi's at all but rather represent ...'plant people'.
Here's the representation again, this time on a tablet from Harappa
Not one of those postures that I've spent much time working on, below is the only picture I have attempting it, notice how high I am how low, settled and... comfortable Krishnamacharya looks in his above.
Having practiced/attempted it a few times, I'm going with the argument that this is a posture you need to work at and work towards via a lot of other hip opening asana, and over an extended period of time, suggesting that there was a postural practice going on all those thousands of years ago and in the service of meditation.
Looking at the seals and that wonderful picture of K. tempts me to work on the posture again, wonderful pranayama posture. To do so I'll probably go for more daily practice of as well as extended stays in janushirsasana, mahamudra, viracyasana B, badha konasana,....
Going to get me one of Fred's lodge hats too
see too perhaps this alternative view http://www.triyoga.co.uk/blog-yogas-metamorphisis/