Rioja Lizard

©John Negan

Thanks once again to Jose Bonaparte, who is more and more like one of the past greats of paleontology of the northern hemisphere as the years go by, we have another Argentinian dinosaur to study. This time we have the prosauropod Riojasaurus incertus, whose name means Rioja lizard, after the La Rioja region of Argentina. One of two genera found within the family riojasauridae, Riojasaurus is a 33 foot (10 meter) long Late Triassic dinosaur that resembles Massaspondylus and other prosauropods in many ways. All prosauropods resemble their descendants the sauropods in many ways as well including the incorporation into their body structure of hollow vertebrae and massively built and strong limbs both fore and hind as well as a long neck and tail. Riojasaurus, and a close cousin Melanorosaurus, were more massively built than earlier prosauropods leading paleontologists to surmise that Riojasaurus, and Melanorosaurus, may have been the most direct links to the early sauropods from the prosauropods; Peter Galton and Paul Sereno are in the process of detailing an alternate theory to the rise of prosauropods and sauropods that involves a common ancestor. Other important anatomical features, such as the number of vertebrae and the structure of the teeth of Riojasaurus provide additional clues as to it's links to later dinosaurs.