Groeberiidae is a family of strange non- placental mammals from the

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

and

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

epochs of Patagonia,

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 ...

and

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

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 southe ...

. Originally classified as paucituberculate

marsupials 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 po ...

, they were suggested to be late representatives of the

allothere Allotheria (meaning "other beasts", from the Greek , '–other and , '–wild animal) is an extinct branch of successful Mesozoic mammals. The most important characteristic was the presence of lower molariform teeth equipped with two longitudi ...

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 Paleogene (and possibly much earlier, if '' Allostaff ...

. 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 a ...

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, in ...

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 paucituberculate

. Though currently represented only by shrew opossums, through most of the Cenozoic Paucituberculata also included a variety of

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 na ...

-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 diprotodontians, 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 well ...

'' incertae sedis'', both of which contested. More recently, '' Groeberia'' has been understood to be a gondwanathere multituberculate, 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''. 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 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 t ...

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 extant ...

within Diprotodontia, 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 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 po ...

standards, they are now fairly typical among multituberculate standards, even being closely compared to ''

Vintana ''Vintana sertichi'' (from Malagasy vintana, "luck" ) is an early groundhog-like 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 Maastrichti ...

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

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 an ...

, and was probably a generalist herbivore, but other possible taxa like '' Epiklohnia'' do possess

hypsodonty 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 ...

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 well ...

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 thoug ...

, as well as odd placental groups such as

meridiungulates South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals of controversial affinities that were indigenous to South America prior to the Great American Biotic Interchange. They comprise five major groups c ...

and xenarthrans. The first South American

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 a ...

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 Gondwanatheres Cenozoic mammals of South America Prehistoric mammals of South America Oligocene extinctions Prehistoric mammal families Taxa named by Bryan Patterson