Plateosauridae

The Plateosaurids or Prosauropods were a group of early herbivorous dinosaurs that lived during the later Triassic and early Jurassic periods. 
They were the largest herbivores in their environment, and quickly reached (6 to 10 meters long). All prosauropods had a long neck and small head, forelimbs shorter than the hindlimbs, and a very large thumb claw for defense. They were originally thought to be the ancestors of the sauropods, but are now considered by some as a parallel lineage.