|Riojasaurus skull cast|
Riojasaurus (meaning "Rioja lizard") was a herbivorous sauropodomorph dinosaur named after La Rioja Province in Argentina where it was found by José Bonaparte. It lived during the Late Triassic and grew to about 10 metres (33 ft) long. Riojasaurus is the only known riojasaurid to live in South America.
Riojasaurus had a heavy body, bulky legs, and a long neck and tail. Its leg bones were dense and massive for an early sauropodomorph. By contrast, its vertebrae were lightened by hollow cavities, and unlike most early sauropodomorphs, Riojasaurus had four sacral vertebrae instead of three. It has been thought it probably moved slowly on all fours and was unable to rear up on its back legs. The nearly equal length of the fore and hindlimbs has also been interpreted as suggestive of an obligatorily quadrupedal gait. However, in 2016, Scott Hartman found the hand anatomy, relatively straight back and largely immobile shoulder girdle of Riojasaurus supported it being a biped.
No skull was found with the first skeleton of Riojasaurus, although a well-preserved skull attributed to Riojasaurus was found later. The teeth of Riojasaurus were leaf shaped and serrated. The upper jaw contained 5 teeth at the front, with 24 more behind them in a row that ended under the eyes.
Many scientists think that Riojasaurus was closely related to Melanorosaurus, known from the Triassic-Early Jurassic period. However, studies at Bristol University, England, suggest that it is unique in some key ways, such as the longer bones in its neck. It is certainly quite different from other sauropodomorphs found in the Los Colorados Formation of Argentina.
- "Riojasaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 41. ISBN 0-7853-0443-6.
- Van Heerden, J. and Galton, P.M. (1997). "The affinities of Melanorosaurus a Late Triassic prosauropod dinosaur from South Africa". Neues Jahrbuch für Geologie und Paläontologie Monatshefte. (1):39-55
- Hartman, Scott. "La Rioja's ponderous biped".
- Bonaparte, J.F. (1967). Dos nuevas "faunas" de reptiles triásicos de Argentina. Ameghiniana 10(1): 89-102.
- Bonaparte, J.F. & Pumares, J.A. (1995). Notas sobre el primer craneo de Riojasaurus incertus (Dinosauria, Prosauropoda, Melanorosauridae) del Triasico Superios de La Rioja, Argentina. Ameghiniana 32(4): 341-349.
- Schmitz, L.; Motani, R. (2011). "Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology". Science. 332 (6030): 705–8. Bibcode:2011Sci...332..705S. doi:10.1126/science.1200043. PMID 21493820.
- Moody, Richard. Dinofile. pg 20. Octopus Publishing Group Ltd., 2006
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