The constituent parts of Riojasaurus are interesting. As a prosauropod, if we agree that prosauropods were a building block in sauropod evolution and not a convergently evolving group of animals, it makes sense that the body of Riojasaurus, being a later Triassic prosauropod, would be bulking up as it evolved traits more often found in its later descendants the sauropods. These of course included the traits easily visible from afar such as a long neck and a long tail. They also include rather thick strong bones in the legs as well as other parts of the body such as the ribs which made the living animal a massive, heavily built, and strong dinosaur. Another trait found in both Riojasaurus and later sauropods is that their vertebrae were pocked by hollow cavities which lightened the bones. This makes sense for a number of reasons.
One reason of course would be to lighten the neck and tail as well as the back itself so that the weight of the animal was not too much for the legs to handle; the heavily built legs more than likely could have withstood the additional weight of solid bones regardless. The second reason that this makes sense is that had it been able to rear up, current speculations say that this was not possible on account of an extra sacral (pelvic) vertebrae and the near identical length of fore and hind limbs as well as the solidity of their makeup, this would have lightened the pressure on the hips and balancing tail, should that have ever met the ground in the process. There is also the possibility, of course, that nerves and blood vessels inhabited the cavities and helped relay messages and nutrients along the length of the body in a more protected manner, given that they were in the bone for some of their journey.
The skull shows serrated leaf shaped teeth with 5 aligned in the front and 24 behind them in a short mouth that ends under the eyes. Additionally, the eyes possessed sclerotic rings, the small bones that are found around the actual eye ball in a lot of animals, mammals and crocodiles being notable exceptions. The sclerotic rings of Riojasaurus show evidence that this dinosaur was rather sloth-like in its daily activities, taking long breaks from activity and being active at short intervals in daylight.