The Anacleto Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

with

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

s in the

Argentine Argentines, Argentinians or Argentineans are people from Argentina. This connection may be residential, legal, historical, or cultural. For most Argentines, several (or all) of these connections exist and are collectively the source of their ...

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

n provinces of Mendoza, Río Negro, and

Neuquén Neuquén (; ) is the capital city of the Argentine province of Neuquén and of the Confluencia Department, located in the east of the province. It occupies a strip of land west of the confluence of the Limay and Neuquén rivers which form t ...

. It is the youngest formation within the

Neuquén Group The Neuquén Group is a geologic unit, group of geologic formations found in Argentina. Rocks in the Neuquén Group fall within the Cenomanian to early Campanian stages of the Late Cretaceous Period. It overlies the older Lohan Cura Formation and ...

and belongs to the Río Colorado Subgroup. Formerly that subgroup was treated as a formation, and the Anacleto Formation was known as the Anacleto Member. The type locality of this formation lies west of the city of

. At its base, the Anacleto Formation conformably overlies the

Bajo de la Carpa Formation The Bajo de la Carpa Formation is a geologic formation of the Neuquén Basin that outcrop, crops out in northern Patagonia, in the provinces of Río Negro Province, Río Negro and Neuquén Province, Neuquén, Argentina. It is the oldest of two for ...

, also of the Río Colorado Subgroup, and it is in turn

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

overlain by the

Allen Formation The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.Salgado et al., 2007 Dinosaur remains are among the fossils that have been recovered from the forma ...

of the younger

Malargüe Group The Malargüe Group is a group of geologic formations of the Neuquén Basin of the Mendoza, Neuquén, Río Negro and La Pampa Provinces in northern Patagonia, Argentina. The formations of the Malargüe Group range in age between the middle Campa ...

. The Anacleto Formation varies between thick, and consists mainly of

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...

s and

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s, purple and dark red in color, deposited in

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

and

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

environments Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...

Geode A geode (; ) is a geology, geological secondary formation within sedimentary rock, sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded. The crys ...

s are often found scattered throughout this formation.

Fossil content

The following animals are known from bones found in the Anacleto Formation: * several species of

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

s * several species of

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

Crocodylomorphs

Dinosaurs

Ornithischians

Sauropods

Nest A nest is a structure built for certain animals to hold Egg (biology), eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of ...

s of

dinosaur egg Dinosaur eggs are the organic vessels in which a dinosaurs, dinosaur embryo develops. When the first scientifically documented remains of non-avian dinosaurs were being described in England during the 1820s, it was presumed that dinosaurs had la ...

s, many with preserved

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

s inside, have been discovered in large quantities at the famous

Auca Mahuevo Auca Mahuevo is a Cretaceous lagerstätte in the eroded badlands of the Patagonian province of Neuquén, Argentina. The sedimentary layers of the Anacleto Formation at Auca Mahuevo were deposited between 83.5 and 79.5 million years before present ...

locality, and have been attributed to titanosaurs.

Theropods

The oldest known unequivocal

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

footprints from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

were discovered in the Anacleto Formation. The small footprints were tentatively assigned to the

ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxon'' comes from the Ancient Greek (''íchnos'') meaning "track" and English , itself derived from ...

'' Aquatilavipes'' and might have been produced by ''

Patagopteryx ''Patagopteryx'' is an extinct monotypic genus of euornithean dinosaurs that lived during the Late Cretaceous, around 80 mya (unit), mya, in what is now the Sierra Barrosa in northwestern Patagonia, Argentina. About the size of a chicken, it is t ...

'' (whose fossils were only found in the Bajo de la Carpa Formation however) or some unknown

wader 245px, A flock of Red_knot.html" ;"title="Dunlins and Red knot">Dunlins and Red knots Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflats in order to foraging, ...

-like bird; they lack a hind toe. ''

Ignotornis ''Ignotornis'' was a bird ichnogenus dating back to the Barremian-Cenomanian of Colorado, Canada and South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korea ...

'' refers to similar footprints made by larger birds with a small hind toe; they might have been left by ''

Neuquenornis ''Neuquenornis volans'' is a species of enantiornithean birds which lived during the late Cretaceous period in today's Patagonia, Argentina. It is the only known species of the genus ''Neuquenornis''. Its fossils were found in the Santonian Bajo ...

'', but this is also only known from the Bajo de la Carpa Formation. Footprints of these two ichnogenera have also been found elsewhere, but it must be understood that assignment to the same ichnogenus does not imply a close relatedness of the organisms that produced these traces, only a similar

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

. Even smaller and somewhat unusual footprints assigned to '' Barrosopus'' are only known from the Anacleto Formation. They were almost certainly made by some tiny theropod, but whether this was a bird is not quite clear: the innermost front toes of the animal leaving these tracks attached in a position higher than the others. In that, and in their dimensions, they are a very close match for the odd-footed

enantiornithine The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and c ...

bird ''

Yungavolucris brevipedalis ''Yungavolucris'' is a genus of enantiornitheans. It contains the single species ''Yungavolucris brevipedalis'', which lived in the Late Cretaceous (Maastrichtian, c.70.6 – 66 mya). The fossil bones were found in the Lecho Formation at ''esta ...

'', but this is only known from the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

Lecho Formation The Lecho Formation is a geological Formation (geology), formation in the Salta Basin of the provinces Jujuy Province, Jujuy and Salta Province, Salta of northwestern Argentina. Its strata date back to the Maastrichtian, Early Maastrichtian, and i ...

which is some 10 million years younger.Chiappe (1993), Coria ''et al.'' (2002), Lockley ''et al.'' (2006)

Squamates

Testudines

References

Bibliography

* Chiappe, Luis M. (1993): Enantiornithine (Aves) Tarsometatarsi from the Cretaceous Lecho Formation of Northwestern Argentina. ''American Museum Novitates'' 3083: 1-27. [English with Spanish abstract
PDF fulltext
* Coria, Rodolfo A.; Currie, Philip J.; Eberth, David & Garrido, Alberto (2002): Bird footprints from the Anacleto Formation (Late Cretaceous), Neuquén, Argentina. ''Ameghiniana'' 39(4): 453-463. [English with Spanish abstract
PDF fulltext
* * * Lockley, Martin; Matsukawa, Masaki; Ohira, Hiroto; Li, Jianjun; Wright, Joanna; White, Diane & Chen, Peiji (2006): Bird tracks from Liaoning Province, China: New insights into avian evolution during the Jurassic-Cretaceous transition. ''Cretaceous Research'' 27(1): 33-43. (HTML abstract). Erratum: * Salgado, L.; Coria, R.A. & Chiappe, Luis M. (2005): Osteology of the sauropod embryos from the Upper Cretaceous of Patagonia. ''Acta Palaeontologica Polonica'' 50(1): 79–92
PDF fulltext
* {{cite journal , last1=Sánchez , first1=María Lidia , last2=Heredia , first2=Susana , last3=Calvo , first3=Jorge O. , year=2006 , title=Paleoambientes sedimentarios del Cretácico Superior de la Formación Plottier (Grupo Neuquén), Departamento Confluencia, Neuquén (Sedimentary paleoenvironments in the Upper Cretaceous Plottier Formation (Neuquen Group), Confluencia, Neuquén) , url=https://www.researchgate.net/publication/262615949 , journal=Revista de la Asociación Geológica Argentina , volume=61 , pages=3–18 , access-date=2019-02-16 , via=ResearchGate