What Car did this Seat Come out of?

73 and 74 Dart Swinger, Dart Sport, Scamp or Duster.

Notice the rounded front corners of the lower portion between the pleated and non pleated portions, the location of the back release and the shape of the hinge covers.

http://www.hamtramck-historical.com/images/dealerships/colorAndTrim/1973/73_Dart0009.jpg