''Patagonia'' is an extinct genus of non-

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...

mammal from the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

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 ...

. Traditionally considered a

metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...

n ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'', one analysis suggested it to be a

gondwanathere Gondwanatheria is an extinct group of mammaliaforms that lived in parts of Gondwana, including Madagascar, India, South America, Africa and Antarctica during the Upper Cretaceous through the Paleogene (and possibly much earlier, if '' Allostaffi ...

. However, this has been rejected by other authors.

Description

Currently, a single species is known, ''Patagonia peregrina'', hailing from the

Colhuehuapian The Colhuehuapian age is a period of geologic time (21.0–17.5 Ma) within the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification in South America. It follows the Deseadan and precedes the Santacrucian a ...

-dating deposits of the Sarmiento Formation,

Chubut Province Chubut ( es, Provincia del Chubut, ; cy, Talaith Chubut) is a province in southern Argentina, situated between the 42nd parallel south (the border with Río Negro Province), the 46th parallel south (bordering Santa Cruz Province), the Andes rang ...

. The holotype, MACN-CH-869, is composed of a semi-complete

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

; isolated upper and lower teeth are also known. The jaw is short and deep, bearing an unfused subvertical

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing togethe ...

and dorsally positioned

masseter In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it ...

ic fossa. The incisors are rootless and extend lingually along the ventral border of the dentary up to the level of molariform 3, and the molariforms are

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...

. The dental formula is: and the molariform elements are identical, so distinction between molars and

premolars The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...

is impossible. Previously, the animal was thought to have canines, but several studies have found them to be a second pair of incisors.Sánchez-Villagra 2000

Classification

Originally, ''Patagonia'' was identified as some sort of

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

mammal. However, due to its highly aberrant attributes, it tended to be singled out in its own order and

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

, Patagonioidea and Patagoniidae.Pascual & Carlini 1987 Some phylogenetic studies recovered it as part of

Paucituberculata Paucituberculata is an order of South American marsupials. Although currently represented only by the seven living species of shrew opossums, this order was formerly much more diverse, with more than 60 extinct species named from the fossil rec ...

, often lined with the equally confounding groeberiids, albeit in a purely provisory manner with no listed synapomorphies, based only on its

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

-like aspects. Recent studies have instead found it to not be a marsupial or other form of metatherian at all, but a

allothere. The supposed "aberrant" traits were claimed to be normal in this clade, and it has been recovered as nesting within the sudamericid assemblage. However, this conclusion has been rejected by other scholars. Allotheria Cladogram Per Chimento 2015

Biology

''Patagonia'' was a fossorial herbivore. Its jaw and dental anatomy is similar to that of burrowing rodents, to the point that the original description referred to it as a "marsupial

tuco-tuco A tuco-tuco is a neotropical rodent in the family Ctenomyidae.Parada, A., G. D’Elia, C.J. Bidau, and E.P. Lessa. 2011. Species Groups and the Evolutionary Diversification of Tuco-Tucos, genus ''Ctenomys'' (Rodentia: Ctenomyidae). ''Journal of M ...

". Like several other

multituberculates Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, a ...

as well as modern

Glires Glires (, Latin ''glīrēs'' 'dormice') is a clade (sometimes ranked as a grandorder) consisting of rodents and lagomorphs ( rabbits, hares, and pikas). The hypothesis that these form a monophyletic group has been long debated based on morp ...

it had rootless incisors, meaning that they never stopped growing. Like other sudamericids it had hypsodont molariforms. This means it was well adapted to chew

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns a ...

, and was most likely a grazer, which coincides with the

plain In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands ...

s environment where it once lived. Like other allotheres its

ic anatomy and molariform orientation suggest that it had a palinal jaw stroke (front-to-back), a chewing style not seen in modern mammals and one of several traits previously considered "aberrant".

Ecology

The

deposits of the Sarmiento Formation show a general steppe or

savanna A savanna or savannah is a mixed woodland- grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...

-like environment, with a high degree of grass

phytoliths Phytoliths (from Greek, "plant stone") are rigid, microscopic structures made of silica, found in some plant tissues and persisting after the decay of the plant. These plants take up silica from the soil, whereupon it is deposited within different ...

, as opposed to earlier

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

environments in the region.Richard H. Madden, Hypsodonty in Mammals This coincides with ''Patagonias burrowing, grazing habits. A large variety of mammal species are known, including

caviomorph Caviomorpha is the rodent infraorder or parvorder that unites all New World hystricognaths. It is supported by both fossil and molecular evidence. The Caviomorpha was for a time considered to be a separate order outside the Rodentia, but is now ...

rodents such as '' Dudumus'', as well as the rodent-like argyrolagoidean paucituberculates. ''Patagonia'' likely avoided competition in its fairly specialised niche.

References

{{Taxonbar, from=Q6066215 Gondwanatheres Miocene mammals of South America Santacrucian Neogene Argentina Fossils of Argentina Fossil taxa described in 1987 Taxa named by Rosendo Pascual Golfo San Jorge Basin Sarmiento Formation