The Mangrullo Formation is an Early Permian (

Artinskian In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of th ...

)

fossiliferous A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

geological 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 ...

in northeastern

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

.Mangrullo Formation
at Fossilworks.orgMangrullo Member
at Fossilworks.org Some authors alternatively group it together with the Paso Aguiar Formation and the Fraile Muerto Formation as the three

subdivisions Subdivision may refer to: Arts and entertainment * Subdivision (metre), in music * ''Subdivision'' (film), 2009 * "Subdivision", an episode of ''Prison Break'' (season 2) * ''Subdivisions'' (EP), by Sinch, 2005 * "Subdivisions" (song), by Rush ...

of the Melo Formation, in which case it is referred to as the Mangrullo Member.Beri et al., 2011 Like the correlated formations of Irati and Whitehill, it is known for its abundant

mesosaur Mesosaurs ("middle lizards") were a group of small aquatic reptiles that lived during the early Permian period, roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic life ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s. It also contains the oldest known '' Konservat-Lagerstätte'' in

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 sout ...

, as well as the oldest known fossils of amniote embryos.

Geology

The Mangrullo Formation is part of the Cerro Largo Group of the

Paraná Basin The Paraná Basin ( pt, Bacia do Paraná, es, Cuenca del Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande d ...

infill In urban planning, infill, or in-fill, is the rededication of land in an urban environment, usually open-space, to new construction. Infill also applies, within an urban polity, to construction on any undeveloped land that is not on the urban ma ...

Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...

and

assemblage correlation with the

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

ian Irati Formation and the

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

n and

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

n Whitehill Formation, of the Paraná Basin and Karoo Basin respectively, puts it at around the

Age (about 279 ± 6

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

). It has a thickness of nearly .De Santa Ana et al., 2006 It consists primarily of

bed A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many beds ...

s of variable thickness of sandy and

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomiti ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and

laminated Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materia ...

oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...

, claystone, and siltstone.Piñeiro et al., 2012a

Fossil biota

Fossil plants found in the formation include

petrified In geology, petrifaction or petrification () is the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals. Petrified wood typifies this proce ...

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...

and other remains from conifers,

seed fern A seed is an Plant embryogenesis, embryonic plant enclosed in a testa (botany), protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, includ ...

s (notably ''

Gangamopteris ''Gangamopteris'' is a genus of Carboniferous-Permian plants, very similar to ''Glossopteris''. Previously, it was classified as fern with reproduction by seed. The genus is usually only applied to leaves, making it a form taxon. ''Gangamopteri ...

''), and various

palynomorph Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and ''-logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposit ...

s. Invertebrate fossils include bivalves,

clam shrimp Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classifi ...

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

wings ( Hemiptera and Coleoptera of '' Paracicadopsis mendezalzolai'', '' Barona arcuata'' and '' Perlapsocus formosoi''),Pinto et al., 2000 pygocephalomorphs, and '' Chondrites''. Vertebrate fossils include fragmentary remains of

actinistia The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...

ns (coelacanths) and

actinopterygians Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

(tentatively identified as belonging to Elonichthyidae), possible

ichnofossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s of acanthodians ('' Undichna insolentia''), and numerous and well-preserved skulls and partial skeletons of

s ('' Stereosternum'' and ''

Mesosaurus ''Mesosaurus'' (meaning "middle lizard") is an extinct genus of reptile from the Cisuralian, Early Permian of southern Africa and South America. Along with it, the genera ''Brazilosaurus'' and ''Stereosternum'', it is a member of the family (bio ...

'').Mones, 1972 The Mangrullo Formation is notable for being the oldest known '' Konservat-Lagerstätte'' in

. Fossils in some layers are exceptionally preserved, retaining details of soft tissue (including bone sutures, blood vessels, and nerves).

Coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...

s and gut contents of mesosaurs reveal that they preyed mainly on pygocephalomorph

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s and may have engaged in cannibalism. It is also the source of several fossil embryos, a

hatchling In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well. Fish Fish hatchlings generally do not receive parental care, similar to ...

, and very small mesosaurids; all of which are the oldest known evidence of amniotic

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the s ...

.Piñeiro et al., 2012b

Taphonomy

The locality is believed to have been a shallow

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...

-like inland sea. Its early conditions were probably estuarine or

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estu ...

, and the fossils found in the lower mudstone and claystone layers are of bioturbating invertebrates, bivalves and fish. It had an open coastal barrier to marine water but also had extensive inflow of freshwater from melting glaciers. Overlying the earlier mudstone and claystone layers is a layer of limestone deposited with noticeable rippling, an effect of wave motion on very shallow sediment. It is believed that the connection to the sea was lost and the basin gradually began to dry out, becoming more and more

hypersaline A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride, brines, and other salts, with saline levels surpassing that of ocean water (3.5%, i.e. ). Specific microbial species can thrive in hi ...

as it became shallower. It produced

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

conditions near the bottom which resulted in the exceptional preservation of fossils during this period. Most of the earlier organisms disappeared and was replaced by mesosaurs and pygocephalomorphs, both inferred to have been capable of tolerating hypersaline environments. The connection to the sea was reestablished later on in the top layers, and fossils of mesosaurs disappeared to be replaced once again by fish and bioturbating organisms.

Gallery

280 Ma plate tectonic reconstruction.png, Early Permian paleogeography Mangrullo Formation Mesosaurus tenuidens.jpg, ''Mesosaurus tenuidens'' Mangrullo Formation Mesosaurus tenuidens 2.jpg, ''M. tenuidens'' Mangrullo Formation mesosaurid fossils.jpg, Mesosaurid fossils Mangrullo Formation mesosaurid palate.jpg, Mesosaurid palate Mangrullo Formation mesosaurid skull.jpg, Mesosaurid skull Mesosaurus sea.png, "''Mesosaurus'' Sea" Mangrullo Formation mesosaurid skull and description.jpg, Mesosaurid skull and description Mangrullo Formation mesosaurid skeleton and gypsum.jpg, Mesosaurid skeleton and gypsum Mangrullo Formation pygocephalomorph fossils.jpg, Pygocephalomorph fossils Mangrullo Formation pygocephalomorph fossils 2.jpg, Pygocephalomorph fossils Mangrullo Formation algal mats.jpg, Algal mats Stereosternum.jpg, Artist's reconstruction of '' Stereosternum''

References

Bibliography