''Riojasaurus'' (meaning "lizard from

La Rioja La Rioja () is an autonomous communities in Spain, autonomous community and provinces of Spain, province in Spain, in the north of the Iberian Peninsula. Its capital is Logroño. Other List of municipalities in La Rioja, cities and towns in the ...

") was a

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...

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

named after La Rioja Province in

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

where it was found in the Los Colorados Formation in the Ischigualasto-Villa Unión Basin by

José Bonaparte José Fernando Bonaparte (14 June 1928–18 February 2020) was an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists. He has been described by paleontologist ...

. It lived during the

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

(

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

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.

Discovery and naming

''Riojasaurus incertus'' was named by Bonaparte (1969) and was based on the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen, PVL 3808, which was discovered in 1966 and consists of a postcranial skeleton which lacks the skull and mandibles, but preserves 6 presacral vertebrae, diverse caudals, both scapulae, the ischia, and the bones of the hand. In total, at least twenty specimens have been assigned to ''R. incertus'', and the first cranial material of ''R. incertus'' was discovered in 1987 and described in 1995. In 1994, 56 caudal vertebrae from one specimen, and a cast of the skull of ''Riojasaurus incertus'', along with several other specimens, were stolen from the National University of La Rioja in Argentina.Hultz, Thomas R. "Missing La Rioja Specimens." Missing La Rioja Specimens. N.p., 1994. Web. 05 Mar. 2017. . As of 2023, the whereabouts of the stolen fossils are unknown.

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 Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...

estimated its length at and its weight at . Large individuals were estimated to have reached long and weighed . By contrast, its vertebrae were lightened by hollow cavities, and unlike most early sauropodomorphs, ''Riojasaurus'' had four

sacral vertebrae The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

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 Quadrupedalism is a form of Animal locomotion, locomotion in which animals have four legs that are used to weight-bearing, bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four l ...

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 rings of ''Riojasaurus'' and modern birds and reptiles suggest that it may have been

cathemeral Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ...

, active throughout the day at short intervals.

Classification

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

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

period. However, studies at

Bristol University The University of Bristol is a public research university in Bristol, England. It received its royal charter in 1909, although it can trace its roots to a Merchant Venturers' school founded in 1595 and University College, Bristol, which had ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

, 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 Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

References

External links

{{Portal bar, Dinosaurs Massopoda Dinosaur genera Norian dinosaurs Los Colorados Formation Taxa named by José Bonaparte Fossil taxa described in 1969 Dinosaurs of Argentina