Riojasaurus
"La Rioja lizard"
- Lived
- 227 to 206 million years ago, Late Triassic
- Length
- about 5.2 m (17 ft)
- Group
- Early sauropodomorphs, Riojasauridae
- Found in
- Argentina
- Named by
- Bonaparte 1969
Size comparison
To scale
Scale in metersOutline: typical early sauropodomorph shape
Where its fossils were found
The evidence
Today
220 million years ago
Habitat
The Los Colorados Formation records river channels and floodplains with seasonal dry conditions in Argentina. Coloradisaurus, Lessemsaurus and Zupaysaurus lived in this landscape.
Field notes
About Riojasaurus
What it was like
Riojasaurus was a large plant eater with a long neck, a small head and a heavy body. It was one of the biggest land animals of its time. It was about 5 meters (17 feet) long. It probably walked on all fours.
Its world
It lived in the Late Triassic, in what is now Argentina. It comes from the Los Colorados Formation, where it shared the land with the plant eaters Coloradisaurus and Lessemsaurus and the predator Zupaysaurus.
How it was found
Bonaparte named Riojasaurus in 1969. Many skeletons have been found, making it one of the best known Triassic dinosaurs from South America.
Field gallery
More views of Riojasaurus
Scenes reconstructed from the available fossil evidence.
Lived alongside
Found in the same rock formations
A rock formation can hold fossils laid down millions of years apart, so not every animal here met Riojasaurus.
The evidence
The science behind Riojasaurus
Which parts of the picture come from its own bones, and which come from its relatives.
From its own fossils
- Many skeletons preserve its long neck, heavy body and strong limbs.
- An almost complete skull and lower jaws show rather cone-shaped teeth.
- Growth marks in thigh bones record pauses in growth.
Borrowed from relatives
- Almost the whole body is known from its own bones, so its basic outline needs little borrowing from relatives.
Still unknown
- Its skin texture and color.
- Exactly which plants it ate.
- Whether it lived in herds or cared for its young.
Discovery timeline
- 1969Named itBonaparte
- 2004Its worldArcucci, Marsicano & Caselli
- 2007Family treeYates
- 2017Growing upCerda et al.
Key papers
The research behind what we know of Riojasaurus
Named it
Named Riojasaurus among the reptiles of the Late Triassic in Argentina.
Dos nuevas "faunas" de reptiles triasicos de Argentina [Two new reptilian "faunas" of the Argentine Triassic]. Gondwana Stratigraphy (IUGS Symposium, Buenos Aires) 2: 283-306
No link available
Its world
Examined the animals and depositional setting of the Los Colorados Formation, placing its land fauna in the Late Triassic.
Tetrapod association and palaeoenvironment of the Los Colorados Formation (Argentina): a significant sample from Western Gondwana at the end of the Triassic. Geobios 37: 557-568
Read the paper : Tetrapod association and palaeoenvironment of the Los Colorados Formation (Argentina): a significant sample from Western Gondwana at the end of the Triassic (opens in a new tab)Family tree
Linked Eucnemesaurus with Riojasaurus through shared thigh-bone features and established a family for them.
Solving a dinosaurian puzzle: the identity ofAliwalia rexGalton. Historical Biology 19: 93-123
Read the paper : Solving a dinosaurian puzzle: the identity ofAliwalia rexGalton (opens in a new tab)Growing up
Studied thigh-bone tissue and found that Riojasaurus grew in cycles, with a smaller specimen more mature than a larger one.
Novel insight into the origin of the growth dynamics of sauropod dinosaurs. PLOS ONE 12: e0179707
Read the paper : Novel insight into the origin of the growth dynamics of sauropod dinosaurs (opens in a new tab)
Close relatives
Other members of Riojasauridae
Sources: Wikidata