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 outcrops in the

Argentine Argentines (mistakenly translated Argentineans in the past; in Spanish (masculine) or (feminine)) are people identified with the country of Argentina. This connection may be residential, legal, historical or cultural. For most Argentines, s ...

Patagonian Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

provinces of Mendoza, Río Negro, and Neuquén. It is the youngest formation within the Neuquén Group and belongs to the

Río Colorado Subgroup The Río Colorado Subgroup, formerly named as Río Colorado Formation, is a Late Cretaceous (Santonian to Early Campanian) geologic subgroup of the Neuquén Basin in northern Patagonia, Argentina. It belongs to the Neuquén Group and contains the ...

. 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 Neuquén. At its base, the Anacleto Formation conformably overlies the Bajo de la Carpa Formation, 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 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 Campan ...

. 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, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

s, purple and dark red in color, deposited in

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

, lacustrine and

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

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

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

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 Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

s * several species of

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

Crocodylomorphs

Dinosaurs

Ornithischians

Sauropods

Nests of dinosaur eggs, many with preserved

embryo An embryo is an initial stage of development of 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 spe ...

s inside, have been discovered in large quantities at the famous Auca Mahuevo locality, and have been attributed to titanosaurs.

Theropods

The oldest known unequivocal

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

footprints from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

were discovered in the Anacleto Formation. The small footprints were tentatively assigned to the ichnogenus '' Aquatilavipes'' and might have been produced by ''

Patagopteryx ''Patagopteryx'' is an extinct monotypic genus of patagopterygiforms that lived during the Late Cretaceous, around 80 mya, in what is now the Sierra Barrosa in northwestern Patagonia, Argentina. About the size of a chicken, it is the earliest ...

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

wader 245px, A flock of Dunlins and Red knots">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 mudflat ...

-like bird; they lack a hind toe. '' Ignotornis'' refers to similar footprints made by larger birds with a small hind toe; they might have been left by ''

Neuquenornis ''Neuquenornis volans''Chiappe, Luis M.,Calvo, Jorge O. (1994) "Neuquenornis volans, a New Late Cretaceous Bird (Enantiornithes: Avisauridae) from Patagonia, Argentina""Journal of Vertebrate Paleontology" Vol. 14, No. 2 (Jun. 22, 1994), pp. 230- ...

'', 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 cla ...

bird ''

Yungavolucris brevipedalis ''Yungavolucris'' is a genus of enantiornithean birds. 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 '' ...

'', but this is only known from the

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

Lecho Formation The Lecho Formation is a geological formation in the Salta Basin of the provinces Jujuy and Salta of northwestern Argentina. Its strata date back to the Early Maastrichtian, and is a unit of the Salta Group. The fine-grained bioturbated sandston ...

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
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* 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
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* {{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