| Riojasaurids | |
|---|---|
 | |
| Riojasaurus skull cast | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Massopoda |
| Clade: | †Riojasauridae Yates, 2007 |
| Genera | |
Riojasauridae is an extinctfamily ofsauropodomorphdinosaurs from theLate Triassic Period (lateCarnian toNorian Ages). It contains thegeneraRiojasaurus andEucnemesaurus. The Riojasauridae is considered astem taxon, and is defined as "the most inclusive clade containingRiojasaurus incertus but notPlateosaurus engelhardti,Massospondylus carinatus, orAnchisaurus polyzelus".[1]Geologic formations containing riojasaurid fossils include the LowerElliot Formation ofOrange Free State,South Africa (where fossils ofEucnemesaurus have been found), and theLos Colorados Formation, inLa Rioja Province,Argentina (where fossils ofRiojasaurus have been recovered).[1]
The Riojasauridae are considered to be sauropodomorphs, but not sauropods themselves. This means that they were generally much smaller than the Sauropods of theJurassic andCretaceous Periods, and members of this family may not have beenobligatequadrupeds, the way more derived Sauropods were. The relationships of this family within other sauropodomorphs has been considered by studies in 2007[1] and 2020[2] with slightly different results.
Thecladogram below shows basal sauropodomorph relationships simplified after Yates, 2007. In this analysis, Riojasauridae was recovered as the earliest-diverging lineage of the cladeMassopoda, and represents asister group to the node formed byMassospondylidae, the genusJingshanosaurus and theAnchisauria.[1]
The following cladogram is from a phylogenetic analysis by Peyre de Fabrègueset al., 2020. Here, Riojasauridae was placed in a more derived position, lying closer toSauropoda than toMassospondylidae, and appearing as theout group to the clade formed by the genusSeitaad and the Sauropodiformes.[2] The Massospondylidae and the taxa considered to be related to the family by Yates, are shown to be represent more primitive lineages.[2]
