The second clip comes to us from Paleoworld, another PBS documentary, and is not as descriptive of the entire world around Herrerasaurus as the other documentary. Enjoy both videos, then move down to talk about the hand and feet.
Video has been taken down
Now, on to those hands and feet. The hand of Herrerasaurus was elongated after emanating from a short forearm. The first three digits of the hand (including the thumb) are clawed and curved, ideal for grasping prey. The fourth and fifth digits are very small, clawless, and basically not visible in the hand itself when fleshed out. This template for hand molding would continue in the theropods until they reached their pinnacle, in this form, as the claws of Allosaurus which were both strong and sharpened into deadly claws. After Allosaurus the skulls of large theropods became longer and larger and the claws and hands became less important. The other animals to continue to build off of this basal manus are the dromaeosaurs, which retained a grasping hand able to accurately and agilely grab at their prey as they attacked and ate. If Herrerasaurus is indeed a template for the sauropodomorphs of later times, these distant descendants radically changed the manus, retaining more digits than large theropods and changing the overall function of the manus.
The feet and legs of Herrerasaurus are what set it apart from previous reptiles. The hips are no longer splayed and are built strongly enough and openly enough, to support, with the tail, the front of the body without relying upon the arms and manus for support. A fully bipedal animal has many, many advantages in locomotion over its prey and rival predators when they are all fully quadrupedal or partially bipedal. This does not only include movement speed, but the height advantage allows for a larger field of vision in all directions than does being stuck with your head in the bushes or below the bushes. Speed was, however, an advantage that Herrerasaurus did also possess over its rivals and prey. The short thigh, strong legs, and long feet indicate a quick animal (the strong, long tail also indicated being built for speed). On the pes itself digit three was the longest with two and four splayed out to help bear the weight of the animal on these three digits. Digit one was held much like the dew claw of dogs or the rear facing claw of birds with a small claw while digit five was nothing more than a nub of bone.