This was an early concept for the transformation of the Griggs character in the helicopter scene.
Alec Gillis suggested a slow distortion of the face, with a deep split running up from his throat which would disgorge the unpleasant protuberances depicted here.
It was felt that the extended legs were too reminiscent of a fantasy creature, so they were reverted to normal human proportions in the maquette.
I based the withered, bent back upper body on Joel Peter Witkin's portrait of "The Goddess Bunny."
Some background info on the unused Pilot Alien.
Basically the spaceship would have been originally crewed by an alien race which, as it was relayed to me, would have been on a planet to planet zoological expedition, collecting different creatures and storing them in these containment pods.
One of those creatures just happened to be The Thing in disguise, and the rest is history.