The Star Beast

"The Star Beast" was the working title of the script by Dan O'Bannon that would eventually become "Alien".  It went through a myriad of changes during development, particularly in the depiction of the xenomorph itself.  At one point Ron Cobb had a pseudo-quadruped concept for the adult form.
 

When H. R. Giger was brought on board his initial design for the chestburster drew on that depiction before his far more effective bipedal creature was finalized.

Sadly, the so-called "killer turkey" chestburster looked ridiculous due to the limitations of 70s puppetry technology, pushing the production to the iconic design we're all familiar with today.  Now, all these years later, Patrick Magee brings us this amazing recreation of the proto-chestburster based on Giger's artwork.