Exafroplacentalia or Notolegia is a
clade of
placental mammals
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 ...
proposed in 2001 on the basis of molecular research.
Exafroplacentalia places
Xenarthra
Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. ...
as a sister group to the
Boreoeutheria
Boreoeutheria (, "northern true beasts") is a magnorder of placental mammals that groups together superorders Euarchontoglires and Laurasiatheria. With a few exceptionsExceptional clades whose males lack the usual boreoeutherian scrotum are mo ...
(comprising
Laurasiatheria
Laurasiatheria ("laurasian beasts") is a superorder of placental mammals that groups together true insectivores ( eulipotyphlans), bats ( chiropterans), carnivorans, pangolins ( pholidotes), even-toed ungulates ( artiodactyls), odd-toed ungulat ...
and
Euarchontoglires
Euarchontoglires (synonymous with Supraprimates) is a clade and a superorder of mammals, the living members of which belong to one of the five following groups: rodents, lagomorphs, treeshrews, colugos, and primates.
Evolutionary affinities wi ...
),
thus making Afrotheria a primitive group of placental mammals (the group name roughly means "those which are not African placentals").
Classification
However, this classification makes the autapomorphy (character shared only among Exafroplacentalia) dubious: it is hard to classify a group by the absence of a feature (in this case "not coming from Africa").
[Nishihara, H., Maruyama, S. & Okada, N. 2009. Retroposon analysis and recent geological data suggest near-simultaneous divergence of the three superorders of placental mammals. PNAS 106: 5235-40.] Hence, several alternative hypotheses can be considered.
Alternative hypotheses
One alternative hypothesis is the
Epitheria hypothesis:
Another alternative hypothesis is the
Atlantogenata
Atlantogenata is a proposed clade of mammals containing the cohorts or superorders Xenarthra and Afrotheria. These groups originated and radiated in the South American and African continents, respectively, presumably in the Cretaceous. Together ...
hypothesis:
Updated analysis of
transposable element
A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transp ...
insertions around the time of divergence strongly supports the fourth hypothesis of a near-concomitant origin of the three superorders of mammals:
See also
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Epitheria
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Atlantogenata
Atlantogenata is a proposed clade of mammals containing the cohorts or superorders Xenarthra and Afrotheria. These groups originated and radiated in the South American and African continents, respectively, presumably in the Cretaceous. Together ...
References
Further reading
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{{Taxonbar, from=Q133342
Obsolete mammal taxa