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

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

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 lon ...

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 second-largest country in South America after Brazil, th ...

where it was found in the

Los Colorados Formation The Los Colorados Formation is a sedimentary rock formation of the Ischigualasto-Villa Unión Basin, found in the provinces of San Juan and La Rioja in Argentina. The formation dates back to the Norian age of the Late Triassic. The up to thick f ...

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 and the northeastern part of ...

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 . One of the best-known Argentine paleo ...

. 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 ...

(

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

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 Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

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 The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, 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 ...

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 locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...

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 bel ...

s 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 ar ...

, active throughout the day at short intervals.

Classification

Many scientists think that ''Riojasaurus'' was closely related to ''

Melanorosaurus ''Melanorosaurus'' (meaning "Black Mountain Lizard", from the Greek ''melas/'', "black", ''oros/'', "mountain" + ''/'', "lizard") is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period. A herbivore from South Af ...

'', 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 period ...

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-J ...

period. However, studies at

Bristol University , mottoeng = earningpromotes one's innate power (from Horace, ''Ode 4.4'') , established = 1595 – Merchant Venturers School1876 – University College, Bristol1909 – received royal charter , type ...

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 b ...

, 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

.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 bo ...

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