Riojasaurus

Taxobox
name = "Riojasaurus"


image_width = 240px
fossil_range = Late Triassic
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Sauropodomorpha
infraordo = Prosauropoda
familia = Riojasauridae
genus = "Riojasaurus"
genus_authority=Bonaparte, 1969
subdivision_ranks=Species
subdivision=
*"R. incertus" Bonaparte, 1969 (type)

"Riojasaurus" (meaning "Rioja lizard") was a herbivorous prosauropod 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 long (33 ft)."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.] "Riojasaurus" is the only known Riojasaurid to live in South America.

Description

"Riojasaurus" had a heavy body, bulky legs, and a long neck and tail. Its leg bones were dense and massive for a prosauropod. By contrast, its vertebrae were lightened by hollow cavities, and unlike most prosauropods, "Riojasaurus" had four sacral vertebrae instead of three. It probably moved slowly on all fours and was unable to rear up on its back legs.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] The nearly equal length of the fore and hindlimbs is also suggestive of an obligatorily quadrupedal gait.

No skull was found with the first skeleton of "Riojasaurus",Fact|date=July 2008 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.

Classification

Many scientists think that "Riojasaurus" was closely related to "Melanorosaurus", the largest prosauropod known from the Triassic-Early Jurassic era. 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 prosauropods found in the Los Colorados Formation of Argentina. [Moody, Richard. Dinofile. pg 20. Octopus Publishing Group Ltd., 2006]

Due to their size and limb anatomy "Riojasaurus" and the possibly related "Melanorosaurus" have been considered close relatives of the earliest sauropods. However, if the hypothesis proposed by Peter Galton and Paul Sereno is correct, namely that prosauropods and true sauropods share a common ancestor rather than the former giving rise to the latter, than commonalities shared by "Riojasaurus" and true sauropods are likely due to convergent evolution.

References