Early Triassic (215Ma) from southern Argentina [AC checking info with Ale]. Eggs and hatchlings were discovered in the 1970s, but adults were not described until 2013. There is now a good record of their growth series from babies (20cm long) to juveniles and adults (up to 6m long).
Large, robust and probably bipedal as adults, and herbivorous. Young Mussaurus may have been quadrupedal (arms and legs are similar sizes; unlike adults).
Mussaurus was a sauropodomorph, and like the later sauropods (e.g. Diplodocus) that it was a close cousin to, had a long neck and long tail. It thus should help reveal how sauropodomorphs began to become transform into the giant sauropods across the Triassic-Jurassic transition.