Anacleto Formation
Encyclopedia
The Anacleto Formation is a geologic formation
with outcrop
pings in the Argentine
Patagonian provinces of Mendoza
, Río Negro
, and Neuquén
. It is the youngest formation within the Neuquén Group
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 40 kilometers 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
overlain by the Allen Formation
of the younger Malargüe Group
.
The Anacleto Formation varies between 60 and 90 meters thick, and consists mainly of claystone
s and mudstone
s, purple
and dark red in color, of fluvial
origin. Geode
s are often found scattered throughout this formation.
Period: Late Cretaceous
Faunal stage
: early Campanian
Absolute Age
: ~83 to ~78 mya
Nest
s of dinosaur egg
s, many with preserved embryo
s inside, have been discovered in large quantities at the famous Auca Mahuevo
locality, and have been attributed to titanosaurs.
Known from bones found in the Anacleto Formation are:
The oldest known unequivocal bird
footprints from South America
were also discovered in the Anacleto Formation. The small footprints were tentatively assigned to the ichnogenus Aquatilavipes and might have been produced by Patagopteryx
(whose fossils were only found in the Bajo de la Carpa Formation however) or some unknown wader
-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
, 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
.
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 bird Yungavolucris brevipedalis, but this is only known from the Maastrichtian
Lecho Formation
which is some 10 million years younger.
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
with outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
pings in the Argentine
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
Patagonian provinces of Mendoza
Mendoza Province
The Province of Mendoza is a province of Argentina, located in the western central part of the country in the Cuyo region. It borders to the north with San Juan, the south with La Pampa and Neuquén, the east with San Luis, and to the west with the republic of Chile; the international limit is...
, Río Negro
Río Negro Province
Río Negro is a province of Argentina, located at the northern edge of Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean.Its capital is Viedma...
, and Neuquén
Neuquén Province
Neuquén is a province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west...
. It is the youngest formation within the Neuquén Group
Neuquén Group
The Neuquén Group is a 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, about 100 million to 80 million years in age...
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 40 kilometers west of the city of Neuquén
Neuquén
Neuquén is the name of the following things:* Neuquén, Argentina* Neuquén Province* Neuquén River* Neuquén Group...
. At its base, the Anacleto Formation conformably overlies the Bajo de la Carpa Formation
Bajo de la Carpa Formation
The Bajo de la Carpa Formation is a geologic formation that outcrops in Patagonia, in the provinces of Río Negro and Neuquén, Argentina. It is the first of two formations belonging to the Río Colorado Subgroup within the Neuquén Group...
, also of the Río Colorado Subgroup, and it is in turn unconformably
Unconformity
An unconformity is a buried erosion 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 of time before deposition of the younger, but the term is used to describe...
overlain by the Allen Formation
Allen Formation
The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous The Allen Formation is a geological formation in Argentina whose strata date back to the...
of the younger Malargüe Group
Malargüe Group
The Malargüe Group is a group of geologic formations found in Argentina. Rocks in the Malargüe Group fall within the late Campanian to Danian stages of the Late Cretaceous Period, about 80 million to 61.7 million years in age...
.
The Anacleto Formation varies between 60 and 90 meters thick, and consists mainly of claystone
Claystone
Claystone is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles ....
s and mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
s, purple
and dark red in color, of fluvial
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
origin. Geode
Geode
Geodes are geological secondary sedimentary structures which occur in sedimentary and certain volcanic rocks. Geodes are essentially spherical masses of mineral matter that were deposited sygenetically within the rock formations they are found in. Geodes have a Chalcedony shell containing...
s are often found scattered throughout this formation.
Age
Era: MesozoicMesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Period: Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
: early Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
Absolute Age
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
: ~83 to ~78 mya
Fauna
Nest
A nest is a place of refuge to hold an animal's eggs or provide a place to live or raise offspring. They are usually made of some organic material such as twigs, grass, and leaves; or may simply be a depression in the ground, or a hole in a tree, rock or building...
s of dinosaur egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s, many with preserved embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s inside, have been discovered in large quantities at the famous Auca Mahuevo
Auca Mahuevo
Auca Mahuevo is a Cretaceous lagerstätte in the eroded badlands of the Patagonian province of Neuquen, Argentina. The sedimentary layers at Auca Mahuevo were laid down 80 million years before present and offer a view of a fossilized titanosaurid sauropod hatchery.At Auca Mahuevo dinosaur eggs...
locality, and have been attributed to titanosaurs.
Known from bones found in the Anacleto Formation are:
- AerosteonAerosteonAerosteon is a genus of allosauroid theropod dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the Anacleto Formation, dating to the Santonian stage . The type and only known species is A. riocoloradensis...
. - several species of lizardLizardLizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s - an ornithopodOrnithopodOrnithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
(GasparinisauraGasparinisauraGasparinisaura is a genus of ornithopod dinosaur from the Late Cretaceous. Its fossils were found in Argentina. The type species, Gasparinisaura cincosaltensis, was described in 1996 by Coria and Salgado. Originally classified as an iguanodont, recent research indicates it is more basal...
) - titanosaurian sauropods (Antarctosaurus wichmannianus, PellegrinisaurusPellegrinisaurusPellegrinisaurus is the name given to a genus of dinosaur from the Late Cretaceous. It was a titanosaur which lived in what is now Argentina. The type species, Pellegrinisaurus powelli, was described by Salgado in 1996, and is based on mostly vertebrae...
, BarrosasaurusBarrosasaurusBarrosasaurus is a genus of titanosaurian sauropod dinosaur, first described by Leonardo Salgado and Rodolfo Coria in 2009. The fossils, consisting of three fossil dorsal vertebrae, are well-preserved but incomplete. They were discovered in the Anacleto Formation of the Neuquén province of western...
) - ceratosauriaCeratosauriaCeratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
n theropods (AbelisaurusAbelisaurusAbelisaurus is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Period of what is now South America. It was a bipedal carnivore that probably reached 7 to 9 meters in length, although it is known from only one partial skull.The generic name recognizes Roberto Abel as the...
, AucasaurusAucasaurusAucasaurus was a genus of medium-sized theropod dinosaur from Argentina that lived during the Santonian stage . It was smaller than the related Carnotaurus, although more derived in some ways, such as its extremely reduced arms and almost total lack of fingers.The type skeleton is complete to the...
) - some other theropod remains
- several species of mammalMammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s
The oldest known unequivocal bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
footprints from South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
were also discovered in the Anacleto Formation. The small footprints were tentatively assigned to the ichnogenus Aquatilavipes and might have been produced by Patagopteryx
Patagopteryx
Patagopteryx is an extinct monotypic genus of birds 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 known unequivocal example of secondary flightlessness: its skeleton...
(whose fossils were only found in the Bajo de la Carpa Formation however) or some unknown wader
Wader
Waders, called shorebirds in North America , are members of the order Charadriiformes, excluding the more marine web-footed seabird groups. The latter are the skuas , gulls , terns , skimmers , and auks...
-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
Neuquenornis volans was an enantiornithine bird which lived during the Late Cretaceous in today's Patagonia, Argentina. It is presently the only known species of the genus Neuquenornis. Its fossils were found in the Santonian Bajo de la Carpa Formation, dating from about 85-83 million years ago....
, 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 (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
.
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 bird Yungavolucris brevipedalis, but this is only known from the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
Lecho Formation
Lecho Formation
The Lecho Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation....
which is some 10 million years younger.