Allen Formation

Allen Formation
Geological formation
Age	Mid Campanian-Maastrichtian ~
Period	Campanian
Prilithology	Mudstone, sandstone
Otherlithology	Limestone
Namedby	Uliana & Dellapé
Year ts	1981
Region	Neuquén, Río Negro & La Pampa Provinces
Country	Argentina
Coordinates	40.0°S 66.6°W
Paleocoordinates	42.8°S 52.2°W
Unitof	Malargüe Group
Underlies	Jagüel Formation
Overlies	Anacleto Formation
Thickness	up to 70 m (230 ft)
Extent	Neuquén Basin

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]

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.^[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]

A study of pollen found in outcrops of the middle member of the Allen Formation supported a late Maastrichtian age for these layers.^[6]

Fossil content

Dinosaurs

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

Ornithischians

Ankylosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ankylosauria^[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 probable parankylosaur^[9]

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	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^[10]
Lapampasaurus	L. cholinoi	Islas Malvinas	Lower	Elements of the axial and appendicular skeleton of a subadult individual	A hadrosaur^[11]
Willinakaqe	W. salitralensis	Salitral Moreno site.	Lower	A right premaxilla.	A saurolophine hadrosaur^[12]

Saurischians

Sauropods

Genus	Species	Stratigraphic position	Material	Notes
Aeolosaurus	Indeterminate	Lower		A titanosaur^[7]
Bonatitan	B.reigi^[13]	Lower	Braincases, caudal vertebrae, and several limb elements	A titanosaur^[13]
Menucocelsior	M. arriagadai	Lower	Seventeen caudal vertebrae and several appendicular bones: a right humerus, a left fibula and some metapodial.	A titanosaur^[14]
Panamericansaurus	P. schroederi		"Five tail vertebrata, sacral vertebrae, left humerus and rib fragments"	A titanosaur^[7]^[15]
Pellegrinisaurus?	P. powelli	Lower (if it is from the formation)	"Dorsal and caudal vertebrae, partial femur"	A titanosaur^[7]^[15]
Rocasaurus	R. muniozi	Middle	"Partial postcranial skeleton"	A titanosaur^[7]^[16]

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 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^[17]
Limenavis	L. patagonica	Lower	"Partial forelimb"	An ornithuran^[7]^[18]
Niebla	N. antiqua	Upper	Braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs, and incomplete vertebrae.	An abelisaurid^[19]
Quilmesaurus	Q. curriei	Upper	Femur and distal tibia	An abelisaurid^[7]^[20]

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 from South-America^[21]

Fish

Genus^[3]	Species	Material	Notes
Atlantoceratodus	A. patagonicus	3 tooth plates	A ceratorontiform lungfish^[22]
Belonostomus	B. lamarquensis		A aspidorhynchid fish^[23]
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]^[24]	Species	Location	Stratigraphic position	Material	Notes
Alamitophis	A. argentinus			incomplete trunk vertebra
Madtsoiidae	indeterminate			incomplete trunk vertebra
Paleoteius ^[25]	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	Notes
Iaremys	I. batrachomorpha	A chelid turtle^[26]
Trapalcochelys	T. sulcata	A meiolaniform turtle^[27]
Yaminuechelys	Y. gasperinii	A chelid turtle

Rhynchocephalia

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Lamarquesaurus	L. cabazai	Cerro Tortuga			^[28]

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.^[29]^[3]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Calyptocephalella	C. satan	Cerro Tortuga	Lower	A right incomplete maxilla.	A calyptocephalellid frog^[30]
Kuruleufenia	K. xenopoides	Cerro Tortuga, Bajo Santa Rosa, and Cerro Bonaparte	Lower	An almost complete sphenethmoid.	Pipid frog^[31]

Mammals

The mammal fauna of the Allen Formation is known from seven teeth, which document the presence of several species.^[32]

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.^[33]
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.^[34]	Lower	Fossil wood^[34]	A conifer tree
Wintucycas^[35]	W. stevensonii	Salitral Ojo de Agua, Río Negro Province.	Lower	Silicificated cycad trunks	An encephalartoid cycad

References

^ Salgado et al. 2007.
^ Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, South America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 600-604. ISBN 0-520-24209-2.
^ Martinelli, Agustín & Forasiepi, Analía (2004). "Late Cretaceous vertebrates from bajo de Santa Rosa (Allen Formation), Río Negro province, Argentina, with the description of a new sauropod dinosaur (Titanosauridae)". Revista del Museo Argentino de Ciencias Naturales. 6 (2): 257–305. doi:10.22179/REVMACN.6.88
^ Armas & Sánchez 2015, p. 101.
^ Armas & Sánchez 2015, p. 110.
^ Pincheira, Egly Pérez & Garrido, Alberto Carlos (November 2024). "Palynostratigraphy from the Allen and Jagüel formations at the Cerro Gutiérrez locality, Lago Pellegrini area, South Argentina". Journal of South American Earth Sciences. 148. Bibcode:2024JSAES.14805139P. doi:10.1016/j.jsames.2024.105139
^ Weishampel et al., 2004, p.604
^ Álvarez Nogueira, Rodrigo; Agnolín, Federico L.; Rozadilla, Sebastián; Aranciaga-Rolando, Mauro; Novas, Fernando E. (2 January 2025). "Ankylosaurian remains from a new Campanian–Maastrichtian locality in Northern Patagonia, Argentina". Alcheringa: An Australasian Journal of Palaeontology. 49 (1): 69–78. Bibcode:2025Alch...49...69A. doi:10.1080/03115518.2025.2467462
^ Soto Acuña, Sergio; Vargas, Alexander O.; Kaluza, Jonatan (2024). "A new look at the first dinosaur discovered in Antarctica: reappraisal of Antarctopelta oliveroi (Ankylosauria: Parankylosauria)". Advances in Polar Science. 35 (1): 78–107. doi:10.12429/j.advps.2023.0036
^ Rozadilla, Sebastián; Brissón-Egli, Federico; Agnolín, Federico Lisandro; Aranciaga-Rolando, Alexis Mauro; Novas, Fernando Emilio (2 September 2021). "A new hadrosaurid (Dinosauria: Ornithischia) from the Late Cretaceous of northern Patagonia and the radiation of South American hadrosaurids". Journal of Systematic Palaeontology. 19 (17): 1207–1235. Bibcode:2021JSPal..19.1207R. doi:10.1080/14772019.2021.2020917
^ Coria, Riga & Casadío 2012.
^ Juárez Valieri et al., 2010
^ "63.10 Provincia de Río Negro, Argentina; 4. Río Colorado Formation," in Weishampel, et al. (2004). Page 604.
^ Rolando et al., 2022
^ "Table 13.1," in Weishampel, et al., 2004, p.269
^ "Table 13.1," in Weishampel, et al., 2004, p.270
^ Agnolin, 2010
^ "Table 11.1," in Weishampel, et al., 2004, p.215
^ Aranciaga Rolando, Mauro; Cerroni, Mauricio A.; Garcia Marsà, Jordi A.; Agnolín, Federico l.; Motta, Matías J.; Rozadilla, Sebastián; Brisson Eglí, Federico; Novas, Fernando E. (January 2021). "A new medium-sized abelisaurid (Theropoda, Dinosauria) from the late cretaceous (Maastrichtian) Allen Formation of Northern Patagonia, Argentina". Journal of South American Earth Sciences. 105. Bibcode:2021JSAES.10502915A. doi:10.1016/j.jsames.2020.102915. hdl:11336/150468
^ "Table 4.1," in Weishampel, et al., 2004, p.77
^ Novas et al. 2012.
^ Federico Agnolin (2010). "A new species of the genus Atlantoceratodus (Dipnoiformes: Ceratodontoidei) from the Uppermost Cretaceous of Patagonia and a brief overview of fossil dipnoans from the Cretaceous and Paleogene of South America". Brazilian Geographical Journal: Geosciences and Humanities Research Medium. 1 (2): 162–210.
^ Sergio Bogan; Louis Taverne; Federico L. Agnolin (2011). "Description of a new aspidorhynchid fish, Belonostomus lamarquensis sp. nov. (Halecostomi, Aspidorhynchiformes), from the continental Upper Cretaceous of Patagonia, Argentina". Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre. 81: 235–245.
^ Garberoglio, F. F.; Gómez, R. O.; Apesteguía, S.; Rougier, G. W. (2024). "A Late Cretaceous lizard assemblage from the Allen Formation, northern Patagonia, Argentina". Historical Biology: An International Journal of Paleobiology. 37 (4): 950–962. doi:10.1080/08912963.2024.2344789
^ Agnolín, Federico L.; Aranciaga-Rolando, Mauro; Álvarez-Herrera, Gerardo; Ezcurra, Martín D.; Rodríguez, Ana Moreno; Chafrat, Pablo; Vega, Nahuel; Scanferla, Agustín; Smith, Krister T.; Novas, Fernando E. (2026-02-28). "A new late Cretaceous squamate from Patagonia sheds light on Gondwanan diversity". Scientific Reports. doi:10.1038/s41598-026-40914-8. ISSN 2045-2322
^ Agnolín, F. L.; Aranciaga-Rolando, A. M.; Ortiz, R. (2024). "New chelid turtle with a flattened skull from the Late Cretaceous of Northern Patagonia, Argentina". Alcheringa: An Australasian Journal of Palaeontology. 49: 79–84. doi:10.1080/03115518.2024.2427261
^ Sterli, Juliana; Fuente, Marcelo S. De La; Cerda, Ignacio A. (April 2013). "A New Species of Meiolaniform Turtle and a Revision of the Late Cretaceous Meiolaniformes of South America". Ameghiniana. 50 (2): 240–256. Bibcode:2013Amegh..50..240S. doi:10.5710/amgh.16.01.2013.582
^ Apesteguía & Rougier, 2007, p.3
^ Suazo Lara, F. & Gómez, R.O. (March 2022). "In the shadow of dinosaurs: Late Cretaceous frogs are distinct components of a widespread tetrapod assemblage across Argentinean and Chilean Patagonia". Cretaceous Research. 131. Bibcode:2022CrRes.13105085S. doi:10.1016/j.cretres.2021.105085
^ Federico Agnolin (2012). "A new Calyptocephalellidae (Anura, Neobatrachia) from the Upper Cretaceous of Patagonia, Argentina, with comments on its systematic position". Studia Geologica Salmanticensia. 48 (2): 129–178.
^ Gómez, Raúl O. (July 2016). "A new pipid frog from the Upper Cretaceous of Patagonia and early evolution of crown-group Pipidae". Cretaceous Research. 62: 52–64. Bibcode:2016CrRes..62...52G. doi:10.1016/j.cretres.2016.02.006. hdl:11336/59544
^ Rougier et al., 2009
^ Connelly, B. E.; Cardozo, M. S.; Montgomery, J. D.; Rougier, G. W. (2024). "New mammals from the Upper Cretaceous Allen Formation (Patagonia, Argentina) and reassessment of meridiolestidan diversity". Cretaceous Research. 162. Bibcode:2024CrRes.16205935C. doi:10.1016/j.cretres.2024.105935
^ Passalia, M.G.; Garrido, A.; Iglesias, A.; Vera, E.I. (February 2023). "The Valcheta Petrified Forest (Upper Cretaceous), northern Patagonia, Argentina: A geological and paleobotanical survey". Cretaceous Research. 142. Bibcode:2023CrRes.14205395P. doi:10.1016/j.cretres.2022.105395
^ Leandro Carlos Alcides Martinez; Analia Emilia Eva Artabe; Josefina Bodnar (2012). "A new cycad stem from the Cretaceous in Argentina and its phylogenetic relationships with other Cycadales". Botanical Journal of the Linnean Society. 170 (3): 436–458. doi:10.1111/j.1095-8339.2012.01300.x

Bibliography

Agnolin, Federico L (2010), "An avian coracoid from the Upper Cretaceous of Patagonia, Argentina", Studia Geologica Salmanticensia. 46 (2): 99–119, retrieved 2019-02-16
Apesteguía, Sebastián & Rougier, Guillermo W. (2007). "A Late Campanian Sphenodontid Maxilla from Northern Patagonia". American Museum Novitates. ' (3581): 1. doi:10.1206/0003-0082(2007)3581[1:ALCSMF2.0.CO;2]
Armas, Paula & Sánchez, María Lidia (30 January 2015). "Márgenes costeros híbridos de la Cuenca Neuquina (Formación Allen, Cretácico Superior, Argentina)". Andean Geology. 42 (1). Bibcode:2015AndGe..42a...6A. doi:10.5027/andgeoV42n1-a06
Coria, Rodolfo A.; Riga, Bernardo González; Casadío, Silvio (December 2012). "Un Nuevo Hadrosáurido (Dinosauria, Ornithopoda) de la Formación Allen, Provincia de la Pampa, Argentina". Ameghiniana. 49 (4): 552–572. Bibcode:2012Amegh..49..552C. doi:10.5710/AMGH.9.4.2012.487
Juárez Valieri, Rubén; Haro, José; Fiorelli, Lucas; Calvo, Jorge (2010). "A new hadrosauroid (Dinosauria: Ornithopoda) from the Allen Formation (Late Cretaceous) of Patagonia, Argentina". Revista del Museo Argentino de Ciencias Naturales. 12: 217–231. doi:10.22179/REVMACN.12.242. hdl:11336/147903
Novas, Fernando E.; Kundrat, Martin; Agnolín, Federico L.; Ezcurra, Martín D.; Ahlberg, Per Erik; Isasi, Marcelo P.; Arriagada, Alberto; Chafrat, Pablo (November 2012). "A new large pterosaur from the Late Cretaceous of Patagonia". Journal of Vertebrate Paleontology. 32 (6): 1447–1452. Bibcode:2012JVPal..32.1447N. doi:10.1080/02724634.2012.703979. hdl:11336/98097
Rougier, Guillermo W.; Chornogubsky, Laura; Casadio, Silvio; Arango, Natalia Paéz; Giallombardo, Andres (February 2009). "Mammals from the Allen Formation, Late Cretaceous, Argentina". Cretaceous Research. 30 (1): 223–238. Bibcode:2009CrRes..30..223R. doi:10.1016/j.cretres.2008.07.006. hdl:11336/103413
Salgado, Leonardo; Coria, Rodolfo A.; Magalhaes Ribeiro, Claudia M.; Garrido, Alberto; Rogers, Raymond; Simón, María E.; Arcucci, Andrea B.; Rogers, Kristina Curry; Carabajal, Ariana Paulina; Apesteguía, Sebastián; Fernández, Mariela; García, Rodolfo A.; Talevi, Marianella (June 2007). "Upper Cretaceous dinosaur nesting sites of Río Negro (Salitral Ojo de Agua and Salinas de Trapalcó-Salitral de Santa Rosa), northern Patagonia, Argentina". Cretaceous Research. 28 (3): 392–404. Bibcode:2007CrRes..28..392S. doi:10.1016/j.cretres.2006.06.007. hdl:11336/183909
Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004), The Dinosauria, 2nd edition, Berkeley: University of California Press, pp. 1–880, ISBN 0-520-24209-2, retrieved 2019-02-21