''Riojasaurus'' (meaning "Rioja lizard") was a herbivorous sauropodomorph

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

named after La Rioja Province in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...

where it was found in the Los Colorados Formation in the

Ischigualasto-Villa Unión Basin The Ischigualasto-Villa Unión Basin ( es, Cuenca de Ischigualasto-Villa Unión) is a small sedimentary basin located in the Argentine Northwest, Argentina. It is located in the southwestern part of La Rioja Province, Argentina, La Rioja Province a ...

by José Bonaparte. It lived during the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...

( Norian stage) and grew to about long."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. . ''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 an early sauropodomorph. In 2010 Gregory S. Paul estimated its length at and its weight at . 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.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 has also been interpreted as suggestive of an obligatorily quadrupedal gait, and the relative robustness of the forelimbs and hindlimbs is in the range of quadrupedal animals. However, the morphology of the hand and shoulder girdle has been interpreted as inconsistent with a quadrupedal gait. No skull was found with the first skeleton of ''Riojasaurus'',Bonaparte, J.F. (1969). Dos nuevas "faunas" de reptiles triásicos de Argentina. ''Ameghiniana'' 10(1): 89-102. although a well-preserved skull attributed to ''Riojasaurus'' was found later.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. 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. Comparisons between the

scleral ring Sclerotic rings are rings of bone found in the eyes of many animals in several groups of vertebrates, except for mammals and crocodilians. They can be made up of single bones or multiple segments and take their name from the sclera. They are beli ...

s of ''Riojasaurus'' and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals.

Classification

Many scientists think that ''Riojasaurus'' was closely related to '' Melanorosaurus'', known from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

- Early Jurassic period. However, studies at Bristol University,

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

, 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

.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.

References

External links

{{Portal bar, Dinosaurs Sauropodomorphs Dinosaur genera Norian life Late Triassic dinosaurs of South America Triassic Argentina Fossils of Argentina Los Colorados Formation Fossil taxa described in 1969 Taxa named by José Bonaparte