Groeberiidae is a family of strange 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 distinguished ...

mammals from the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

and

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

epochs of

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

and

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. Originally classified as

paucituberculate 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 reco ...

marsupials Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a ...

, they were suggested to be late representatives of the

allothere Allotheria (meaning "other beasts", from the Greek , '–other and , '–wild animal) is an extinct clade of mammals known from the Mesozoic and early Cenozoic. Shared characteristics of the group are the presence of lower molariform teeth equip ...

clade

Gondwanatheria 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 Miocene (and possibly much earlier, if '' Allostaffia' ...

. However, the relationship of the type genus, '' Groeberia'', to Gondwanatheria has been firmly rejected by other scholars.

History

The type species, '' Groeberia minoprioi'', was first described by

Bryan Patterson Bryan Patterson (born 10 March 1909 in London; died 1 December 1979 in Chicago) was an American paleontologist at the Field Museum of Natural History in Chicago. Life and career Bryan Patterson was the son of the soldier, engineer and author ...

in 1952. This type specimen, MMP 738, is composed of a mandibular symphisis, incisors and four broken molars. A second species within the genus, '' Groeberia pattersoni'', was described by

G. G. Simpson George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...

in 1970, and is known from at least two specimens.Goin, F.J., Abello M.A. & Chornogubsky L. 2010
Middle Tertiary marsupials from Central Patagonia (Early Oligocene of Gran Barranca): Understanding South America’s ''Grande Coupure''
En: Madden R.H., Carlini A.A., Vucetich M.G. & Kay R.F. (Eds.), ''The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia''. Cambridge University Press. Both occur in the

Divisadero Largo Formation __NOTOC__ Divisadero may refer to: Places Mexico * Divisadero, Chihuahua, a town on the Ferrocarril Chihuahua al Pacífico (Copper Canyon railroad) * Divisaderos, Sonora United States * Divisadero Street, in San Francisco * Divisadero Street, ...

deposits dating to the

. Flynn & Wyss, 1999 would go on to describe the

species '' Klohnia charrieri'', and Goin ''et al''., 2010 the taxa '' Klohnia major'', '' Epiklohnia verticalis'' and '' Praedens aberrans'', all also dating to this epoch. Recently, Chimento ''et al''. 2013 re-examined '' Groeberia'' and understood its

affinities. Other taxa were not included in this examination for so far unspecified reasons, rendering their status as part of the clade unknown.

Classification

For most of their history, groeberiids were thought to be

. Though currently represented only by

shrew opossum The family Caenolestidae contains the seven surviving species of shrew opossum: small, shrew-like marsupials that are confined to the Andes mountains of South America. The order is thought to have diverged from the ancestral marsupial line very e ...

s, through most of the Cenozoic Paucituberculata also included a variety of

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

-like species, making this assessment somewhat sound. However, this classification was provisory at best, as compared to other paucituberculates groeberiids were highly aberrant. A few differing opinions included Simpson & Wyss 1999, which considered these animals to be

diprotodontia Diprotodontia (, from Greek language, Greek "two forward teeth") is the largest extant order (biology), order of marsupials, with about 155 species, including the kangaroos, Wallaby, wallabies, Phalangeriformes, possums, koala, wombats, and many ...

ns, and Pascual 1994 and Simpson 1970, which saw them as

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 ...

incertae sedis or is a term used for a taxonomy (biology), 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, uncertainty ...

'', both of which contested. More recently, '' Groeberia'' has been understood 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 Miocene (and possibly much earlier, if '' Allostaffia' ...

multituberculate 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 ...

, a group in which its "aberrant" attributes turned out to be fairly typical. Within Gondwanatheria, it stands in a fairly basal position, having diverged before the diverse sudamericids but after ''

Ferugliotherium ''Ferugliotherium'' is a genus of fossil mammals in the family Ferugliotheriidae from the Campanian and/or Maastrichtian period (Late Cretaceous; around 70 million years ago) of Argentina. It contains a single species, ''Ferugliotherium windhaus ...

''. Other groeberiids have not been included in this analysis; whereas they're gondwanatheres or paucituberculates is yet to be determined. Well before this reassignment,

Malcolm McKenna Malcolm Carnegie McKenna (1930–2008) was an American paleontologist and author on the subject. Paleontologist McKenna began his paleontology career at the Webb School of California (grades 9-12) in Claremont, California, under noted paleontolo ...

expressed doubts on a marsupial identity for groeberiids, claiming that considering them metatherians was "an act of faith". However, Zimicz & Goin (2020) claimed that the anatomy of the teeth of ''Groeberia'' supports the metatherian affinities of this taxon. The phylogenetic analysis conducted by these authors recovered ''Groeberia'' as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

Vombatiformes The Vombatiformes are one of the three suborders of the large marsupial order Diprotodontia. Seven of the nine known families within this suborder are extinct; only the families Phascolarctidae, with the koala, and Vombatidae, with three ext ...

within

Diprotodontia Diprotodontia (, from Greek language, Greek "two forward teeth") is the largest extant order (biology), order of marsupials, with about 155 species, including the kangaroos, Wallaby, wallabies, Phalangeriformes, possums, koala, wombats, and many ...

, though the authors cautioned that these results are preliminary.

Characteristics

Groeberiids possess robust, deep snouts bearing elongated incisors and molariforme

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

adapted for a palinal (front-to-back) jaw stroke; once considered aberrant by

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

standards, they are now fairly typical among

standards, even being closely compared to ''

Vintana ''Vintana sertichi'' is an early gondwanatherian mammal dating from the Late Cretaceous, approximately 66 million years ago. Scientists found the lone fossil, a skull, on Madagascar's west coast in the Maastrichtian Maevarano Formation. ''Vintan ...

''. They were almost certainly herbivores; '' Groeberia'' itself, unlike more derived gondwanatheres like sudamericids, lacked the specializations to cope with

grass Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family (biology), family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and spe ...

, and was probably a generalist herbivore, but other possible taxa like '' Epiklohnia'' do possess hypsodonty and are thought to be grazers.

Ecology

Groeberiids co-existed with a variety of other mammal groups, such as

and other

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 ...

ns such as

sparassodonts Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now though ...

, as well as odd

groups such as meridiungulates and

xenarthra Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a superorder and major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and ...

ns. The first South American

caviomorph Caviomorpha is the rodent 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 accepted as ...

rodents are thought to have arrived to the continent roughly at the time these gondwanatheres were alive; competition, if any, between both groups is so far unresolved, though groeberiids are speculated to have been fairly specialised. Assuming the genera besides '' Groeberia'' are in fact groeberiids, the group achieved its highest diversity in the mid-

, well after rodents arrived.

Notes

References

{{Taxonbar, from=Q731873 Gondwanatheria Cenozoic mammals of South America Prehistoric mammals of South America Oligocene extinctions Prehistoric mammal families Taxa named by Bryan Patterson