Meridiungulata is an extinct

Extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 clade with the rank of cohort or super-order, containing the South-American ungulate

Ungulate

Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

s: Pyrotheria

Pyrotheria

Pyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera Baguatherium, Carolozittelia, Colombitherium, Gryphodon, Propyrotherium, Proticia, and Pyrotherium....

 (possibly including Xenungulata), Astrapotheria

Astrapotheria

Astrapotheria is an extinct order of South American hoofed animals. The history of this order is enigmatic, but it may taxonomically belong to Meridiungulata . In turn, Meridungulata is believed to belong to the extant superorder Laurasiatheria...

, Notoungulata

Notoungulata

Notoungulata is an extinct order of hoofed, sometimes heavy bodied mammalian ungulates which inhabited South America during the Paleocene to Pleistocene, living from approximately 57 Ma to 11,000 years ago.-Taxonomy:...

 and Litopterna

Litopterna

Litopterna is an extinct order of fossil hoofed mammals from the Tertiary period that displays toe reduction. Three-toed, and even a one-toed horselike form developed....

. Meridiungulata may have originated in South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 from a North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

n condylarth

Condylarth

Condylarthra is an order of extinct placental mammals known primarily from the Paleocene and Eocene epochs. Condylarths are among the most characteristic Paleocene mammals and they illustrate the evolutionary level of the Paleocene mammal fauna....

 ancestor, and they may be members of the clade Laurasiatheria, related to other ungulates including artiodactyls and perissodactyls. It is, however, entirely possible the Meridiungulata are actually part of a different macro-group of placental mammals called Atlantogenata

Atlantogenata

Atlantogenata is a proposed clade of mammals containing the cohorts or super-orders Afrotheria, Xenarthra and Meridiungulata. These groups originated and radiated in the South American and African continents, presumably in the Cretaceous. Together with Boreoeutheria it makes up Eutheria...

.

Much of the evolution of meridiungulates occurred in isolation from other ungulates, a great example of convergent evolution

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

. However, the argument that meridiungulates are related to artiodactyls and perissodactyls will remain tenuous unless DNA is found to confirm this relationship. Some paleontologists have also challenged the monophyly

Monophyly

In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...

 of Meridiungulata by suggesting that pyrotheres may be more closely related to other mammals such as Embrithopoda

Embrithopoda

Embrithopoda is an extinct order of mammals which first appeared in the fossil record during the late Eocene and then died out during the Oligocene....

 (an African order that may be related to elephant

Elephant

Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...

s) than to other South American ungulates.

Most litopterns and notoungulates died out following the invasion of South America by North American ungulates and predators during the Great American Interchange

Great American Interchange

The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...

; a few species from both orders survived until the end-Pleistocene extinctions.