Ameridelphia is traditionally a
superorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
that includes all
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 ...
s living in the
Americas
The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. ...
except for the
Monito del monte
The monito del monte or colocolo opossum, ''Dromiciops gliroides'', also called ''chumaihuén'' in Mapudungun, is a diminutive marsupial native only to southwestern South America (Argentina and Chile). It is the only extant species in the ancient ...
(''Dromiciops''). It is now regarded as a
paraphyletic
In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
group.
Orders
The
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
s within this group are listed below:
* Order
Didelphimorphia (108 species)
** Family
Didelphidae: opossums
* Order
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 re ...
(7 species)
**Family
Caenolestidae: shrew opossums
Evolution and phylogenetics
Modern marsupials are now understood to be an originally South American lineage that later reached Australia and diversified there in a massive
adaptive radiation
In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic in ...
.
Molecular data, including analysis of
retrotransposon
Retrotransposons (also called Class I transposable elements or transposons via RNA intermediates) are a type of genetic component that copy and paste themselves into different genomic locations ( transposon) by converting RNA back into DNA throu ...
insertion sites in the
nuclear DNA
Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. I ...
of a variety of marsupials, and the fossil evidence indicate that Ameridelphia might best be understood as an
evolutionary grade. Since Didelphimorphia appears to be the
basal marsupial group, it and Paucituberculata do not seem to be closest relatives.
Meanwhile, the unranked
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
Euaustralidelphia has been proposed as the name for the Australian marsupials (
Australidelphia
Australidelphia is the superorder that contains roughly three-quarters of all marsupials, including all those native to Australasia and a single species — the monito del monte — from South America. All other American marsupials are members o ...
minus
Microbiotheria, of which ''Dromiciops'' is
the only survivor), which in all probability derive from a single colonization out of South America via
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
.
References
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Marsupials
Marsupials of North America
Marsupials of Central America
Marsupials of South America
Mammals of North America
Mammal superorders
Early Cretaceous mammals
Cretaceous mammals of North America
Cretaceous mammals of South America
Cenozoic mammals of North America
Cenozoic mammals of South America
Paraphyletic groups