# Allen Formation

The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian. Dinosaur remains are among the fossils that have been recovered from the formation. Indeterminate chelid remains and other vertebrates have also been discovered in this formation.

## Description

Uliana and Dellapé defined the formation's stratotype in 1981 in the eastern area of the Bajo de Añelo, where the relation between the base and top is clearly exposed. The deposits are mostly clastic, interbedded with banks of limestone and layers of anhydrite, which were defined as continental and shallow marine facies associated with semiarid conditions.
The interpreted sedimentary paleoenvironments range from purely continental such as ephemeral lacustrine, aeolian and fluvial systems to coastal marine paleoenvironments with development of estuaries and tidal flats, followed by a lagoon sedimentary stage from marsh to sea with carbonate precipitation in an area protected from waves, ending with a retraction leading to the accumulation of evaporites.
Armas and Sánchez performed a detailed facies analysis of the formation in 2015, where the authors concluded the formation represents a hybrid coastal system of tidal flats, dominated by Atlantic ingressions, with a large storm influence in some areas linked to aeolian systems.

## Fossil content
### Dinosaurs

| 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. |
Dinosaur eggs are known from the formation.

#### Ornithischians
##### Ankylosaurs

| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Ankylosauria | Indeterminate | Arriagada Farm | | Two teeth, five osteoderms, and a partial sacrum | Fossil remains possibly belonging to a parankylosaur distinct from Patagopelta | |
| Patagopelta | P. cristata | Salitral Moreno locality | Lower | Tooth, three posterior dorsal vertebrae, caudal vertebrae, two caudal centra, right femur, partial cervical half ring, and osteoderms. | A parankylosaur | |

##### Hadrosaurs

| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Bonapartesaurus | B. rionegrensis | Salitral Moreno and Islas Malvinas. | Lower | A partial skeleton. | A hadrosaur |
| Kelumapusaura | K. machi | | Upper | Partial skull, a cervical vertebrae, several sacrals, sternal rib and sternal plate, and multiple referred specimens found in a bonebed | A saurolophine hadrosaur |
| Lapampasaurus | L. cholinoi | | Lower | Elements of the axial and appendicular skeleton of a subadult individual | A hadrosaur |
| Willinakaqe | W. salitralensis | Salitral Moreno site. | Lower | A right premaxilla. | A saurolophine hadrosaur |

#### Saurischians
##### Sauropods

| Genus | Species | Stratigraphic position | Material | Notes |
| Aeolosaurus | Indeterminate | Lower | | A titanosaur |
| Bonatitan | B.reigi | Lower | Braincases, caudal vertebrae, and several limb elements | A titanosaur |
| Menucocelsior | M. arriagadai | Lower | Seventeen caudal vertebrae and several appendicular bones: a right humerus, a left fibula and some metapodial. | A titanosaur |
| Panamericansaurus | P. schroederi | | "Five tail vertebrata, sacral vertebrae, left humerus and rib fragments" | A titanosaur |
| Pellegrinisaurus? | P. powelli | Lower (if it is from the formation) | "Dorsal and caudal vertebrae, partial femur" | A titanosaur |
| Rocasaurus | R. muniozi | Lower | "Partial postcranial skeleton" | A titanosaur |

#### Theropods

| Genus | Species | Stratigraphic position | Material | Notes |
| Austroraptor | A. cabazai | Lower | A fragmentary skeleton including parts of the skull, lower jaw, a few neck and torso vertebrae, some ribs, a humerus, and assorted bones from both legs | A dromaeosaurid |
| Bonapartenykus | B. ultimus | Upper | A holotype consists of a mid-dorsal vertebra, both scapulocoracoids, left tibia and femur, left pubis articulated with the pubic peduncle of the ilium, the anterior blade of the left ilium, and two partially preserved eggs. | An alvarezsauroid |
| Lamarqueavis | L. australis | Lower | "Right coracoid with damaged sternal and omal extremities, and lacking acrocoracoidal process" | An ornithuran |
| Limenavis | L. patagonica | Lower | "Partial forelimb" | An ornithuran |
| Niebla | N. antiqua | Upper | Braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs, and incomplete vertebrae. | An abelisaurid |
| Quilmesaurus | Q. curriei | Upper | Femur and distal tibia | An abelisaurid |

### Pterosaurs

Fragmentary fossils are known from the formation.
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Aerotitan | A. sudamericanus | Bajo de Arriagada | Upper | Partial rostrum | The first unambiguous azhdarchid from South-America | |

### Fish

| Genus | Species | Material | Notes |
| Atlantoceratodus | A. patagonicus | 3 tooth plates | A ceratorontiform lungfish |
| Belonostomus | B. lamarquensis | | A aspidorhynchid fish |
| Chondrichthyes | indeterminate | 11 vertebral centra | |
| Diplomystidae | indeterminate | 4 incomplete pectoral spines | |
| Siluriformes | indeterminate | 5 incomplete pectoral spines | |
| Lepisosteidae | indeterminate | 6 vertebral centra | |
| Teleostei | indeterminate | 10 isolated teeth | |
| cf. Percichthyidae | indeterminate | 19 fragmentary vertebrae | |

### Squamata

| Genus | Species | Material |
| Patagoniophis | P. parvus | incomplete trunk vertebra |
| Alamitophis | A. argentinus | incomplete trunk vertebra |
| Madtsoiidae | indeterminate | incomplete trunk vertebra |
| ?Scincoidea | indeterminate | incomplete left maxilla |
| Pleurodonta | indeterminate | incomplete left maxilla |
| Teiioidea | indeterminate | incomplete right maxilla |

### Turtles

| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Iaremys | I. batrachomorpha | | | | A chelid turtle | |
| Yaminuechelys | Y. gasperinii | | | | A chelid turtle | |

### Rhynchocephalia

| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Lamarquesaurus | L. cabazai | Cerro Tortuga | | | | |

### Plesiosauria

| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Kawanectes | K. lafquenianum | | | | | |

### Frogs

Unnamed frogs belonging to the family Calyptocephalellidae and Leptodactylidae, and those with no family designation were also found.
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Calyptocephalella | C. satan | | | | Calyptocephalellid frog |
| Kuruleufenia | K. xenopoides | | | | Pipid frog | |

### Mammals

The mammal fauna of the Allen Formation is known from seven teeth, which document the presence of several species.
| Genus | Species | Location | Material | Notes |
| Mesungulatum | M. lamarquensis | Cerro Tortuga | Two upper molars and a fragmentary lower molar | A dryolestoid |
| Groebertherium | G. stipanicici | Cerro Tortuga | One upper molar | A dryolestoid |
| cf. Brandonia | sp. | Cerro Tortuga | One lower molar | A dryolestoid |
| Barberenia | B. allenensis | Cerro Tortuga | One upper molariform | A dryolestoid |
| Solanutheirum | S. walshi | Cerro Tortuga | A right lower molar and left dentary fragment. | A meridiolestid. |
| Trapalcotherium | T. matuastensis | Cerro Tortuga | One first lower molar | A gondwanathere |

### Plants

| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Podocarpoxylon | P. mazzonii | Valcheta Petrified Forest, Río Negro Province. | | Fossil wood | | |