Allen Formation
Geological formation in Argentina
The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to late 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.
01Description
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.
A study of pollen found in outcrops of the middle member of the Allen Formation supported a late Maastrichtian age for these layers.
02Fossil content
Dinosaurs
Color key
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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 | Multiple specimens and fragmentary remains, including skull bones, vertebrae, limb bones and girdles, and osteoderms. | A probable parankylosaur |
- Hadrosaurs
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|---|
| Bonapartesaurus | B. rionegrensis | Salitral Moreno and Islas Malvinas. | Lower | A partial skeleton. | A hadrosaur | |
| Kelumapusaura | K. machi | Cerro Matadero, Arriagada Farm | 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 | Islas Malvinas | 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 | Location | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|---|
| Aeolosaurus | Indeterminate | Lower | A titanosaur | |||
|
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 | Middle | "Partial postcranial skeleton" | A titanosaur |
Theropods
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|---|
| 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 | Location | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|---|
| 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 | Location | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|---|
| Alamitophis | A. argentinus | incomplete trunk vertebra | ||||
| Madtsoiidae | indeterminate | incomplete trunk vertebra | ||||
| Paleoteius | P. lakui | Bonapartenykus site on Arriagada Farm | Upper | A specimen consists of a partial skull and skeleton belonging to a single individual. | A lizard | |
| Patagoniophis | P. parvus | incomplete trunk vertebra | ||||
| Pleurodonta | indeterminate | incomplete left maxilla | ||||
| ?Scincoidea | indeterminate | incomplete left maxilla | ||||
| Teiioidea | indeterminate | incomplete right maxilla |
Turtles
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|---|
| Iaremys | I. batrachomorpha | A chelid turtle | ||||
| Trapalcochelys | T. sulcata | A meiolaniform 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 | Quarry of the “Bentonitas Patagónicas” company | Upper | A partial skeleton consists of six cervical vertebrae, three dorsal vertebrae, three sacral vertebrae, nine caudal vertebrae, right femur, right humerus, ilium, one 216 mesopodial element, one caudal phalanx and one caudal rib . | An elasmosaur. |
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 | Cerro Tortuga | Lower | A right incomplete maxilla. | A calyptocephalellid frog | |
| Kuruleufenia | K. xenopoides | Cerro Tortuga, Bajo Santa Rosa, and Cerro Bonaparte | Lower | An almost complete sphenethmoid. | 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 | Images |
|---|---|---|---|---|---|
| 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. | Lower | Fossil wood | A conifer tree | |
| Wintucycas | W. stevensonii | Salitral Ojo de Agua, Río Negro Province. | Lower | Silicificated cycad trunks | An encephalartoid cycad |
Sources and credits
This article is adapted from the Wikipedia article “Allen Formation”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Fms Anacleto Allen Auca Mahuida 1.jpg by Damián H. Zanette, CC BY-SA 4.0
- Allen Formation Fauna.png by PaleoNeolitic, CC BY-SA 4.0
- Quilmesaurus hunting Bonapartesaurus version 2.jpg by ABelov2014, CC BY 3.0
- Patagopelta into the water.png by Gabriel Díaz Yantén (paleogdy), CC BY-SA 4.0
- Bonapartesaurus rionegrensis.png by Connor Ashbridge, CC BY-SA 4.0
- Kelumapusaura.jpg by Leonardo HerSan, CC BY-SA 4.0
- Aeolosaurus-rionegrinus-JD-2020-1.png by Ornithopsis, CC BY 4.0
- Bonatitan reconstruction.png by Atlantis536, CC0
- Rocasaurus muniozi.jpg by Thorfinn777, CC BY 4.0
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