Allen Formation

The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.^[1] Dinosaur remains are among the fossils that have been recovered from the formation.^[2] Indeterminate chelid remains and other vertebrates have also been discovered in this formation.^[3]

Allen Formation
Stratigraphic range: Mid Campanian-Maastrichtian ~73–69 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Outcrop of the Allen and Anacleto Formations at Auca Mahuida
Type	Geological formation
Unit of	Malargüe Group
Underlies	Jagüel Formation
Overlies	Anacleto Formation
Thickness	up to 70 m (230 ft)
Lithology
Primary	Mudstone, sandstone
Other	Limestone
Location
Coordinates	40.0°S 66.6°W / -40.0; -66.6
Approximate paleocoordinates	42.8°S 52.2°W / -42.8; -52.2
Region	Neuquén, Río Negro & La Pampa Provinces
Country	Argentina
Extent	Neuquén Basin
Type section
Named by	Uliana & Dellapé
Year defined	1981
Allen Formation (Argentina)

Description

Fauna of Allen Formation

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.^[4]

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.^[4]

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.^[5]

Fossil content

Life restoration of Dinosaurs discovered from Allen Formation

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.^[6]

Ornithischians

Ankylosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ankylosauria[7]	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[8]

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		Upper	Partial skull, a cervical vertebrae, several sacrals, sternal rib and sternal plate, and multiple referred specimens found in a bonebed	A saurolophine hadrosaur[9]
Lapampasaurus	L. cholinoi		Lower	Elements of the axial and appendicular skeleton of a subadult individual	A hadrosaur[10]
Willinakaqe	W. salitralensis	Salitral Moreno site.	Lower	A right premaxilla.	A saurolophine hadrosaur[11]

Saurischians

Sauropods

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Aeolosaurus	Indeterminate		Lower		A titanosaur[6]
Bonatitan	B.reigi[12]		Lower	Braincases, caudal vertebrae, and several limb elements	A titanosaur[12]
Menucocelsior	M. arriagadai		Lower	Seventeen caudal vertebrae and several appendicular bones: a right humerus, a left fibula and some metapodial.	A titanosaur[13]
Panamericansaurus	P. schroederi			"Five tail vertebrata, sacral vertebrae, left humerus and rib fragments"	A titanosaur[6][14]
Pellegrinisaurus?	P. powelli		Lower (if it is from the formation)	"Dorsal and caudal vertebrae, partial femur"	A titanosaur[6][14]
Rocasaurus	R. muniozi		Lower	"Partial postcranial skeleton"	A titanosaur[6][15]

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[16]
Limenavis	L. patagonica		Lower	"Partial forelimb"	An ornithuran[6][17]
Niebla	N. antiqua		Upper	Braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs, and incomplete vertebrae.	An abelisaurid[18]
Quilmesaurus	Q. curriei		Upper	Femur and distal tibia	An abelisaurid[6][19]

Pterosaurs

Fragmentary fossils are known from the formation.^[6]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Aerotitan	A. sudamericanus	Bajo de Arriagada	Upper	Partial rostrum	The first unambiguous azhdarchid from South-America[20]

Fish

Genus[3]	Species	Location	Stratigraphic position	Material	Notes	Images
Atlantoceratodus	A. patagonicus			3 tooth plates	A ceratorontiform lungfish[21]
Belonostomus	B. lamarquensis				A aspidorhynchid fish[22]
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[3][23]	Species	Location	Stratigraphic position	Material	Notes	Images
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[24]
Trapalcochelys	T. sulcata				A meiolaniform turtle[25]
Yaminuechelys	Y. gasperinii				A chelid turtle

Rhynchocephalia

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Lamarquesaurus	L. cabazai	Cerro Tortuga			[26]

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.^[27][3]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Calyptocephalella	C. satan				Calyptocephalellid frog[28]
Kuruleufenia	K. xenopoides				Pipid frog[29]

Mammals

The mammal fauna of the Allen Formation is known from seven teeth, which document the presence of several species.^[30]

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.[31]
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.[32]		Fossil wood[32]

See also

• List of dinosaur-bearing rock formations
• Adamantina Formation
• La Colonia Formation
• Lecho Formation
• Los Alamitos Formation
• Los Llanos Formation
• Marília Formation