Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of the defining features of marsupials is their unique reproductive strategy, where the young are born in a relatively undeveloped state and then nurtured within a pouch on their mother's abdomen.
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 as many extinct non-marsupial relatives. It is one of two groups placed in the clade Theria alongside Eutheria, which contains the placentals. Remains of metatherians have been found on all of Earths continents.
The monito del monte, or colocolo opossum, is a diminutive species of marsupial native only to south-western South America. It is the only extant species in the ancient order Microbiotheria, and the sole New World representative of the superorder Australidelphia, being more closely related to Australian marsupials than to other American marsupials. The species is nocturnal and arboreal, and lives in thickets of South American mountain bamboo in the Valdivian temperate forests of the southern Andes, aided by its partially prehensile tail. It consumes an omnivorous diet based on insects and fruit.
Microbiotheria is an australidelphian marsupial order that encompasses two families, Microbiotheriidae and Woodburnodontidae, and is represented by only one extant species, the monito del monte, and a number of extinct species known from fossils in South America, Western Antarctica, and northeastern Australia.
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 record, particularly from the late Oligocene to early Miocene epochs. The earliest paucituberculatans date to the late Paleocene. The group went through a pronounced decline in the middle Miocene epoch, which resulted in the extinction of all families of this order except for the living shrew opossums (Caenolestidae). Extinct families of Paucituberculatans include Pichipilidae, Palaeothentidae, and Abderitidae.
Sparassodonta 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 thought to be a separate side branch that split before the last common ancestor of all modern marsupials.
Trigonostylops is an extinct genus of South American meridiungulatan ungulate, from the Late Paleocene to Late Eocene of South America and Antarctica. It is the only member of the family Trigonostylopidae.
Seymour Island or Marambio Island, is an island in the chain of 16 major islands around the tip of the Graham Land on the Antarctic Peninsula. Graham Land is the closest part of Antarctica to South America. It lies within the section of the island chain that resides off the west side of the peninsula's northernmost tip. Within that section, it is separated from Snow Hill Island by Picnic Passage, and sits just east of the larger key, James Ross Island, and its smaller, neighboring island, Vega Island.
Herpetotherium is an extinct genus of metatherian mammal, belonging to the possibly paraphyletic family Herpetotheriidae. Native to North America from the Eocene to Early Miocene, fossils have been found in California, Oregon, Texas, Florida, Montana, Wyoming, Colorado, North and South Dakota, Nebraska, and Saskatchewan. The oldest species, H. knighti, is dated to around 50.3 mya, and the most recent, an unnamed species, may be as recent as 15.97 mya. A morphological analysis of marsupials and basal metatherians conducted in 2007 found Herpetotherium to be the sister group to extant marsupials. It is the youngest known metatherian from North America until the migration of the Virginia opossum from South America within the last 2 million years.
Herpetotheriidae is an extinct family of metatherians, closely related to marsupials. Species of this family are generally reconstructed as terrestrial, and are considered morphologically similar to modern opossums. They are suggested to have been insectivores. Fossils of herpetotheriids come from North America, Asia, Europe, Africa, and perhaps South America. The oldest representative is Maastrichtidelphys from the latest Cretaceous (Maastrichtian) of the Netherlands and the youngest member is Amphiperatherium from the Middle Miocene of Europe. The group has been suggested to be paraphyletic, with an analysis of petrosal anatomy finding that North American Herpetotherium was more closely related to marsupials than the European Peratherium and Amphiperatherium.
Chulpasia is an extinct genus of Eocene marsupial related to today's shrew opossums. It was a small animal, about 20 centimetres (7.9 in) long, with an omnivorous diet. Its diet probably included seeds, small fruits, and insects. Fossils were found in the Muñani Formation in present-day Peru.
Adapisoriculidae is an extinct family of non-placental eutherian mammals which was present during the Paleogene and possibly the Late Cretaceous. They were once thought to be members of the order Erinaceomorpha, closely related to the hedgehog family (Erinaceidae), because of their similar dentition, or to be basal Euarchontans. They were also thought to be marsupials at one point. Most recent studies show them to be non-placental eutherians, however.
The Santa Rosa local fauna consists of the animals found in the Paleogene fossil site of Santa Rosa in eastern Peru. The age of the Santa Rosa fauna is difficult to determine, but may be Eocene (Mustersan) or Oligocene (Deseadan).
The La Meseta Formation is a sedimentary sequence deposited during the Eocene on Seymour Island off the coast of the Antarctic Peninsula. It is noted for its fossils, which include both marine organisms and the only terrestrial vertebrate fossils from the Cenozoic of Antarctica.
Groeberiidae is a family of strange non-placental mammals from the Eocene and Oligocene epochs of Patagonia, Argentina and Chile, South America. Originally classified as paucituberculate marsupials, they were suggested to be late representatives of the allothere clade Gondwanatheria. However, the relationship of the type genus, Groeberia, to Gondwanatheria has been firmly rejected by other scholars.
Polydolopimorphia is an extinct order of metatherians, closely related to extant marsupials. Known from the Paleocene-Pliocene of South America and the Eocene of Antarctica, they were a diverse group during the Paleogene, filling many niches, before declining and becoming extinct at the end of the Neogene. It is divided into two suborders, Bonapartheriiformes, and Polydolopiformes Most members are only known from jaw fragments, which have their characteristically generally bunodont teeth. The morphology of their teeth has led to proposals that polydolopimorphians may be crown group marsupials, nested within Australidelphia, though this proposal, has been questioned, with other analyses finding them outside of crown-group Marsupialia. The monophyly of the group has been questioned, due to the possibility of the characteristic bunodont teeth emerging convergently in unrelated groups, rather than reflecting a true phylogenetic relationship. The group contained omnivorous, frugivorous and herbivorous forms.
The Itaboraí Formation is a highly fossiliferous geologic formation and Lagerstätte of the Itaboraí Basin in Rio de Janeiro, southeastern Brazil. The formation reaching a thickness of 100 metres (330 ft) is the defining unit for the Itaboraian South American land mammal age (SALMA), dating to the Early Eocene, approximately 53 to 50 Ma.
Hondonadia is an extinct genus of Late Eocene to Early Oligocene (Tinguirirican) marsupials related to today's shrew opossums and with similar features as the related Rosendolops. The type species Hondonadia feruglioi was described by Goin and Candela in 1998. In later years, five more species were recognized, of which Pascualdelphys fierroensis, described by Flynn and Wyss in 1999, that was in 2010 synonymized with Hondonadia.
Woodburnodon is an extinct genus of microbiotherian marsupial whose fossils have been found on Seymour Island, Antarctica. It lived during the Eocene epoch.
Sparnotheriodontidae is an enigmatic extinct family of litopterns known primarily from teeth. Sparnotheriodontids are one of two South American native ungulate clades known to have reached Antarctica, the other being astrapotheres.
