The Bajo de la Carpa 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 ...

of the

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The bas ...

that crops out in northern

Patagonia 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 ...

, in the provinces of Río Negro and

Neuquén Neuquén (; arn, Nehuenken) 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 w ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. It is the oldest of two formations belonging 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 ...

within the

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. It overlies the older Lohan Cura Formation and is itself over ...

. Formerly, that subgroup was treated as a formation, and the Bajo de la Carpa Formation was known as the Bajo de la Carpa Member.Sánchez ''et al.'', 2006 At its base, this formation

conformably Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igne ...

overlies the Plottier Formation of the older Río Neuquén Subgroup, and it is in turn overlain by the

Anacleto Formation The Anacleto Formation is a geologic formation with outcrops 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. Formerl ...

, the youngest and uppermost formation of the

. The Bajo de la Carpa Formation can reach in thickness in some locations, and consists mainly of

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

s of various colors, all of

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 ...

origin, with thin layers of

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. ...

and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

in between. Geological features such as

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, chemical nodules, impressions of raindrops, and

paleosol In the geosciences, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The precise definition of the term in geology and paleontology is slightly different from its use in soil science. In geolo ...

s (fossil soils) are commonly found in this formation as well.

Fossil content

Vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

fossils are abundant within the Bajo de la Carpa Formation: * a snake-necked turtle, ''

Lomalatachelys ''Lomalatachelys neuquina'' is an extinct genus and species of chelid turtle from Argentina. The specimen was found in the Loma de La Lata zone approximately 75 km from Neuquen City in north west Patagonia, Argentina Argentina (), ...

'' * a

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 ...

, ''

Paleochelco ''Paleochelco'' is an extinct genus of lizard, possibly a polyglyphanodontian, found in the Late Cretaceous Bajo de la Carpa Formation in Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), i ...

'' * the

snake Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...

Dinilysia ''Dinilysia'' (meaning "terrible ilysia") is an extinct genus of snake from the Late Cretaceous ( Coniacian) of South America. ''Dinilysia'' was a relatively large ambush predator, measuring approximately long. The skull morphology of ''Dinilys ...

'' * diverse

crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cro ...

s occupying a range of

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

s: ''

Comahuesuchus ''Comahuesuchus'' is an extinct genus of notosuchian crocodylomorphs from the Santonian Bajo de la Carpa Formation of Argentina. It was described by palaeontologist José Bonaparte in 1991. The type species is ''C. brachybuccalis''.

'', ''

Cynodontosuchus ''Cynodontosuchus'' is an extinct genus of baurusuchid mesoeucrocodylian. Fossils have been found from Argentina of Late Cretaceous age from the Bajo de la Carpa Formation (dating back to the Santonian), the Pichi Picun Leufu Formation (dating b ...

'', ''

Lomasuchus ''Lomasuchus'' is an extinct genus of peirosaurid notosuchian known from the Late Cretaceous (Santonian stage) of Neuquén Province, western central Argentina. It contains a single species, ''Lomasuchus palpebrosus''. Gasparini, Z., Chiappe, L. ...

'', ''

Gasparinisuchus ''Gasparinisuchus'' is an extinct genus of peirosaurid notosuchian known from the Late Cretaceous (Santonian to early Campanian stage) of Neuquén and Mendoza Provinces, western central Argentina. It contains a single species, ''Gasparinisuchus ...

'',Martinelli et al., 2012 '' Neuquensuchus universitas'',Lio et al., 2018 ''

Notosuchus ''Notosuchus'' (; 'southern crocodile') is an extinct genus of South American notosuchian crocodylomorph. It was terrestrial, living approximately 85 million years ago in the Santonian stage of the Late Cretaceous. Description ''Notosuchus'' wa ...

'', ''

Peirosaurus ''Peirosaurus'' is an extinct genus of peirosaurid crocodylomorph known from the Late Cretaceous period (late Maastrichtian stage) of Minas Gerais, southern Brazil. It contains a single species, ''Peirosaurus torminni''. It is the type genus of ...

'', '' Kinesuchus overoi'',Filippi et al., 2018a and '' Barrosasuchus neuquenianus''Coria et al., 2019 *

titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

s including '' Bonitasaura'', ''

Overosaurus ''Overosaurus'' (meaning "Overo lizard", after the Cerro Overo locality) is an extinct genus of sauropod dinosaurs, containing only a single species, ''Overosaurus paradasorum''. This species lived approximately 86 to 84 million years ago during ...

'', '' Rinconsaurus'', and '' Traukutitan'' * the

ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

s '' Llukalkan'', ''

Velocisaurus ''Velocisaurus'' ("swift lizard") is a genus of noasaurid theropod dinosaur from the Late Cretaceous period of Argentina. Description ''Velocisaurus'' was probably around long, based on a tibia length of . This makes it the smallest noasaur ...

'', and '' Viavenator exxoni''Filippi et al., 2018b * the

megaraptora Megaraptora is a clade of carnivorous Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...

'' Tratayenia rosalesi''Porfiri et al., 2018 * the bird-like theropods '' Achillesaurus'' and ''

Alvarezsaurus ''Alvarezsaurus'' (; "Alvarez's lizard") is a genus of alvarezsaurid dinosaur from the Late Cretaceous, living in Argentina approximately 86 - 83 million years ago. It was a small dinosaur, measuring long and weighing approximately . It was fou ...

'' * the

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 ''

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- ...

'' * the oldest known true

flightless bird Flightless birds are birds that through evolution lost the ability to fly. There are over 60 extant species, including the well known ratites (ostriches, emu, cassowaries, rheas, and kiwi) and penguins. The smallest flightless bird is the In ...

'' Patagopteryx'' * the basal ornithopod '' Mahuidacursor''Cruzado Caballero et al., 2019 * an ankylosaur Small

nest A nest is a structure built for certain animals to hold 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 organic materia ...

s with

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s inside, found in this formation, probably belonged to the bird ''

''.Leanza et al., 2004 Fossil

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...

nests have also been found in these rocks.

References

Bibliography

* * * * * * * * * * *

Fossil content

See also

References

Bibliography

Further reading