# La Colonia Formation

The La Colonia Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.
Originally thought to be Campanian (c.73-72 million years ago) in age or earlier, studies of underlying formations have made a Maastrichtian (72–66 million years ago) age more likely.

## Description

It is divided up into three distinct facies, the first is up to 16 metres (52 ft) thick and consists of conglomerate, the second is by far the thickest at over 100 metres (330 ft), consists of siltstone and claystone, with interbeds of claystone/shale and sandstone, the third is less than 10 metres (33 ft) thick and consists of clay, and probably represents a nearshore marine environment.
The paleoflora was known for its aquatic components, Paleoazolla and Regnellidium. However, recent paleobotanical discoveries at the Cañadón del Irupé locality have revealed the presence of a more diverse range of plants associated with these water bodies, including pteridophytes, gymnosperms, and various angiosperms. Among these are fossil leaves and fruits assignable to Nelumbonaceae.

## Fossil content

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |

### Turtles

Turtles from the La Colonia Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Calvarichelys | C. coloniensis | Norte de Cerro Bayo 2 | Middle levels | Skull and lower jaw; postcranial remains | A chelid |
| Patagoniaemys | P. gasparinae | Buitre Chico in and around Norte de Cerro Bayo 2 Cerro Bosta | | "skull fragments and several postcranial elements including a nearly complete vertebral column." | A meiolaniform |
| Yaminuechelys | aff.Y. gasparinii | Norte de Cerro Bayo 1 Norte de Cerro Bayo 2 Cerro Bosta | | "Three specimens formed only by postcranial remains (mainly shell fragments)" | |
| Yaminuechelys | Y. sulcipeculiaris | Norte de Cerro Bayo 1 Norte de Cerro Bayo 2 Cerro Bosta | | "Three specimens formed only by postcranial remains (mainly shell fragments)" | |

### Fish

Fish from the La Colonia Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Metaceratodus | M. baibianorum | Norte de Cerro Bayo 1 | | | A ceratodontid lungfish | |

### Plesiosaurs

Plesiosaurs from the La Colonia Formation :
| Genus | Species | Location | Material | Notes |
| Chubutinectes | C. carmeloi | | Several vertebrae, ribs, partial pectoral and pelvic girdles, arm and leg bones, and gastroliths | An elasmosaurid |
| Elasmosauridae | Indeterminate | Norte de Cerro Bayo 1 Cerro Bosta | "three postcranial specimens that preserve cervical, dorsal and caudal vertebrae, ribs and gastroliths and three vertebrae without collection number" | |
| Kawanectes | K. lafquenianum | | "an incomplete mandible, nine cervical vertebrae, 14 dorsal vertebrae, three sacral vertebrae and five caudal vertebrae, and almost complete left fore limb, the isolated right humerus, both femora, ilia, pubes and the right ischium" | An elasmosaurid |
| Sulcusuchus | S. erraini | Cerro Bosta | "part of skull and mandible" | A polycotylid |

### Dinosaurs
#### Ornithischians

Ornithischians from the La Colonia Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Ankylosauria | Indeterminate | Norte de Cerro Bayo 2 | | An osteoderm | | |
| Hadrosauroidea | Indeterminate | Norte de Cerro Bayo 2 | | Metatarsal fragment and two vertebral fragments | | |

#### Sauropods

Sauropods from the La Colonia Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Somphospondyli | Indeterminate | Norte de Cerro Bayo 2 | | "Two fragmentary caudal vertebrae" | | |
| Titanomachya | T. gimenezi | Norte de Cerro Bayo 2 | | "Partial postcranial skeleton" | A titanosaur sauropod | |

#### Theropods

Theropods from the La Colonia Formation :
| Genus | Species | Location | Material | Notes |
| Carnotaurus | C. sastrei | Pocho Sastre | "Nearly complete skeleton and skull" | An abelisaurid |
| Enantiornithine | Indeterminate | | A distal humerus | |
| Koleken | K. inakayali | Norte de Cerro Bayo 1 | "Quite complete and partially articulated skeleton" | An abelisaurid. |
| Neornithes | Indeterminate | | A distal ulna | |
| Theropoda | Indeterminate | Norte de Cerro Bayo 2 | "Metatarsal fragments of a single individual" | |

### Mammals

Over 300 mammal specimens have been found in the La Colonia Formation.
Mammals of the La Colonia Formation :
| Genus | Species | Notes |
| Argentodites | A. coloniensis | A possible gondwanatherian or multituberculate |
| Coloniatherium | C. cilinskii | A meridiolestidan |
| Ferugliotherium | F. windhauseni | A possible gondwanatherian or multituberculate |
| Reigitherium | R. bunodontum | A meridiolestidan |

### Snakes

Fossils of madtsoiids, and perhaps boids, have been found in the formation.
Snakes from the La Colonia Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Alamitophis | A. argentinus | | | Trunk vertebra | A madtsoiid snake | |
| Eomadtsoia | E. ragei | | | | A madtsoiid Snake | |