Patanjali Yogsutras were given 4500 years ago and do not give description of any asana. There is only one line - 'sthir sukham asanam'. That is, a posture in which you are still and at peace. So any posture that can be maintained for long hours without movement or discomfort is an asana. Sage Patanjali is called the Fountainhead of Yoga.
The purpose of asana is cleansing the body – nadis (etheric channels) and chakras (energy centres). 4500 years ago, there was no requirement for this cleansing, the thought, actions and environment were relatively pure and conducive to the practice of Yoga. Therefore, no mention of asanas in Patanjali Ashtanga Yoga.
With passage of time, the bodies and minds started becoming polluted as did the environment, therefore various forms of Yoga came in, and around 500 years back, Hatha Yoga was formulated by yogis like Matsyendranath and Gorakhanath which de…