Allen Formation

Allen Formation
Allen Formation
Stratigraphic range: Mid Campanian-Maastrichtian; ~73–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N B V H B Apt. Albian C T C S Cam. M
	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°00′S 66°36′W / 40.0°S 66.6°W
Approximate paleocoordinates	42°48′S 52°12′W / 42.8°S 52.2°W
Region	Neuquén, Río Negro & La Pampa Provinces
Country	Argentina
Extent	Neuquén Basin
Type section
Named by	Uliana & Dellapé
Year defined	1981
	Allen Formation (Argentina)

The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to late Maastrichtian).^[1]^[2] Dinosaur remains are among the fossils that have been recovered from the formation.^[3] Indeterminate chelid remains and other vertebrates have also been discovered in this formation.^[4]

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.^[5]

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.^[5]

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.^[6]

A study of pollen found in outcrops of the middle member of the Allen Formation supported a late Maastrichtian age for these layers.^[2]

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.

Dinosaurs

Dinosaur eggs are known from the formation.^[7]

Ornithischians

Ankylosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ankylosauria Indet.^[8]	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 parankylosaur^[9]

Hadrosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes
Bonapartesaurus	B. rionegrensis	Salitral Moreno and Islas Malvinas.	Lower	A partial skeleton.	A austrokritosaurian saurolophine
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 austrokrytosaurian saurolophine^[10]
Lapampasaurus	L. cholinoi	Islas Malvinas	Lower	Elements of the axial and appendicular skeleton of a subadult individual	A hadrosaurid hadrosaur^[11]
Willinakaqe	W. salitralensis	Salitral Moreno site.	Lower	A right premaxilla.	A saurolophine hadrosaurid^[12]

Saurischians

Sauropods

Genus	Species	Stratigraphic position	Material	Notes	Images
Aeolosaurus	A. rionegrinus	Lower		A aeolosaurin lithostrotian^[13]^[7]	Aeolosaurus Bonatitan Rocasaurus Pellegrinisaurus
Bonatitan	B.reigi^[14]	Lower	Braincases, caudal vertebrae, and several limb elements	A saltasaurin saltasaurine^[14]
Menucocelsior	M. arriagadai	Lower	Seventeen caudal vertebrae and several appendicular bones: a right humerus, a left fibula and some metapodial.	A eutitanosaurian titanosaur^[15]
Panamericansaurus	P. schroederi		"Five tail vertebrata, sacral vertebrae, left humerus and rib fragments"	A aeolosaurin lithostrotian^[7]^[16]
Pellegrinisaurus?	P. powelli	Lower (if it is from the formation)	"Dorsal and caudal vertebrae, partial femur"	A opisthocoelocaudiine saltasaurid^[7]^[16]
Rocasaurus	R. muniozi	Middle	"Partial postcranial skeleton"	A saltasaurin saltasaurine^[7]^[17]
Titanosauria^[18]	indeterminate	Middle	Teeth and partial skeleton	Lacks diagnostic materials to be named.

Theropods

Genus	Species	Stratigraphic position	Material	Notes
Austroraptor	A. cabazai	Lower^{[citation needed]}	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 unenlagiine theropod
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.	A patagonykine alvarezsaurid
Lamarqueavis	L. australis	Lower	"Right coracoid with damaged sternal and omal extremities, and lacking acrocoracoidal process"	A cimolopterygid ornithuran^[19]
Limenavis	L. patagonica	Lower	"Partial forelimb"	A ornithuran bird^[7]^[20]
Niebla	N. antiqua	Upper	Braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs, and incomplete vertebrae.	A brachyrostran abelisaurid^[21]
Quilmesaurus	Q. curriei	Upper	Femur and distal tibia	A carnotaurin furileusaurian^[7]^[22]

Pterosaurs

Fragmentary fossils are known from the formation.^[7]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Aerotitan	A. sudamericanus	Bajo de Arriagada	Upper	Partial rostrum	The first unambiguous azhdarchid pterosaur from South-America^[23]

Fish

Genus^[4]	Species	Material	Notes
Atlantoceratodus	A. patagonicus	3 tooth plates	A ceratorontiform lungfish^[24]
Belonostomus	B. lamarquensis		A aspidorhynchid fish^[25]
Chondrichthyes Indet	indeterminate	11 vertebral centra
Diplomystidae Indet.	indeterminate	4 incomplete pectoral spines
Siluriformes Indet.	indeterminate	5 incomplete pectoral spines
Lepisosteidae Indet	indeterminate	6 vertebral centra
Teleostei Indet.	indeterminate	10 isolated teeth
cf. Percichthyidae Indet.	indeterminate	19 fragmentary vertebrae

Squamata

Genus^[4]^[26]	Species	Location	Stratigraphic position	Material	Notes
Alamitophis	A. argentinus			incomplete trunk vertebra	A madtsoiid snake
Madtsoiidae Indet.	indeterminate			incomplete trunk vertebra
Paleoteius^[27]	P. lakui	Bonapartenykus site on Arriagada Farm	Upper	A specimen consists of a partial skull and skeleton belonging to a single individual.	A scincomorph lizard
Patagoniophis	P. parvus			incomplete trunk vertebra	A madtsoiid snake
Pleurodonta Indet.	indeterminate			incomplete left maxilla
?Scincoidea Indet.	indeterminate			incomplete left maxilla
Teiioidea Indet.	indeterminate			incomplete right maxilla

Turtles

Genus	Species	Notes
Iaremys	I. batrachomorpha	A chelid turtle^[28]
Trapalcochelys	T. sulcata	A meiolaniform turtle^[29]
Yaminuechelys	Y. gasperinii	A chelid turtle

Rhynchocephalia

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Lamarquesaurus	L. cabazai	Cerro Tortuga			A neosphenodontian sphenodontian^[30]

Plesiosauria

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