Riojasauridae is a family of large, heavily built sauropodomorphs from the Late Triassic of Argentina, roughly 221 to 205 million years ago, representing some of the biggest herbivores of their time. Members had a notably robust build compared to most other early sauropodomorphs, with dense, massive limb bones, a long neck and tail, and four sacral vertebrae rather than the three typical of earlier relatives -- a shift toward the heavier, more column-like limb architecture later seen in true sauropods. Body length in the type genus reached over 6.5 meters, substantial for the Triassic.
The type genus, Riojasaurus, was named for La Rioja Province, Argentina, where it was recovered from the Los Colorados Formation, and the family also includes the related genus Eucnemesaurus. Because of their size and heavily built limbs, Riojasaurus and its relatives -- including the somewhat similar Melanorosaurus -- have long been discussed as close relatives of the ancestral stock that gave rise to true sauropods, making Riojasauridae an important reference point for understanding the transition from bipedal early dinosaurs to the quadrupedal giants of the Jurassic.