# 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 600 metres (2,000 ft) thick formation comprises sandstones, siltstones, mudstones and conglomerates with gypsum layers deposited in a fluvial to lacustrine environment. The formation is the uppermost stratigraphic unit of the Agua de la Peña Group, overlying the Lagerstätte of the Ischigualasto Formation. Los Colorados Formation is partly covered by the Cretaceous Cerro Rajado Formation, separated by an unconformity.
The formation is known for its fossils of early dinosaurs, including the coelophysoid Zupaysaurus and the "prosauropods" Coloradisaurus, Lessemsaurus, and Riojasaurus. Magnetostratigraphic analysis suggests that the Los Colorados Formation was deposited between 227 and 213 million years ago.

## Description

Los Colorados Formation is a unit with an approximate thickness of 600 metres (2,000 ft) of the Agua de la Peña Group in the Ischigualasto-Villa Unión Basin, where it is exposed in the Ischigualasto Provincial Park, a World Heritage Site in Argentina. The formation gradually overlies the Ischigualasto Formation and is unconformably overlain by the Cretaceous Cerro Rajado Formation. The formation comprises red-colored, fine- to medium-grain–size sandstones together with siltstones and ancillary floodplain mudstones with early calcisol development. The formation was deposited in a fluvial to lacustrine environment.

## Fossil content
### Anapsids

Anapsids of Los Colorados Formation :
| Genus | Species | Location | Material | Notes | Images |
| Palaeochersis | P. talampayensis | | | | |

### Synapsids

Synapsids of Los Colorados Formation :
| Genus | Species | Material | Notes |
| Chaliminia | C. musteloides | | |
| Jachaleria | J. colorata | A skull and complete jaws. | A Kanemyeriidae dicynodont. |
| Tessellatia | T. bonapartei | A partial skull, including the snout, orbital region, and lower jaws. | A cynodont. |

### Archosauromorphs

Archosauromorphs of Los Colorados Formation :
| Genus | Species | Location | Material | Notes |
| Fasolasuchus | F. tenax | La Rioja Province | A fragmented skull and jaws. | A giant loricatan Pseudosuchian. |
| Neoaetosauroides | N. engaeus | Quebrada de los Jachaleros, El Salto (San Juan) | | An aetosaur. |
| Riojasuchus | R. tenuisceps | | | An ornithosuchid. |

#### Crocodylomorpha

Crocodylomorphs of Los Colorados Formation :
| Genus | Species | Location |
| Coloradisuchus | C. abelini | La Rioja Province |
| Hemiprotosuchus | H. leali | Quebrada de los Jachaleros, El Salto (San Juan) |
| Pseudhesperosuchus | P. jachaleri | Quebrada de los Jachaleros, El Salto (San Juan) |

#### Dinosaurs

Indeterminate theropod remains present in the Provincia de la Rioja.
Dinosaurs of Los Colorados Formation :
| Genus | Species | Location | Material | Notes |
| Coloradisaurus | C. brevis | La Rioja Province | "Skull, adult" | A massospondylid sauropodomorph. |
| Lessemsaurus | L. sauropoides | La Rioja Province | "Partial cervical, dorsal, and sacral vertebrae, adult." | A sauropodiform. |
| Prosauropoda | Indeterminate | La Rioja & San Juan Provinces | Includes Strenusaurus procerus. "Dorsals, caudals, partial fore- and hindlimb." | |
| Powellvenator | P. podocitus | Ischigualasto-Villa Unión Basin | Known from previously undescribed partial hindlimbs | A coelophysoid. |
| Riojasaurus | R. incertus | La Rioja Province | | A sauropodomorph. |
| Zupaysaurus | Z. rougieri | La Rioja Province | | An early theropod. |

### Ichnofossils

* cf. Brachychirotherium sp.
* Chirotherium sp.