Meridiungulata

Meridiungulata
Toxodon platensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Eutheria
Superorder:	Laurasiatheria ?
(unranked):	†Meridiungulata McKenna 1975
Orders
†Pyrotheria (disputed) †Astrapotheria (disputed) †Notoungulata †Litopterna †Xenungulata

Meridiungulata is an extinct clade with the rank of cohort or superorder, containing the South American ungulates Pyrotheria (possibly including Xenungulata), Astrapotheria, Notoungulata and Litopterna. It´s not known if it´s a natural group; it was made to distinguish the ungulates of South America from other ungulates. Relationships between the orders inside Meriungulata remain unresolved and it could well be a 'wastebasket' taxon.

Meridiungulata may have originated in South America from a North American condylarth 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.

Much of the evolution of meridiungulates occurred in isolation from other ungulates, a great example of convergent evolution. 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 of Meridiungulata by suggesting that the pyrotheres may be more closely related to other mammals, such as Embrithopoda (an African order that may be related to elephants), 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; a few species from both orders survived until the end-Pleistocene extinctions.

Classification

Astrapotherium magnum skull

The following classification is from Rose 2006:

• †Meridiungulata

• Amilnedwardsia (Notopterna?)

• Order †Notoungulata

• Suborder †Notioprogonia

• †Henricosborniidae
• †Notostylopidae

• Suborder †Toxodontia

• †Isotemnidae
• †Notohippidae
• †Leontiniidae
• †Toxodontidae
• †Homalodotheriidae

• Suborder Typotheria

• †Oldfieldthomasiidae
• †Interatheriidae
• †Archaeopithecidae
• †Mesotheriidae
• †Campanorcidae

• Suborder Hegetotheria (Typotheria?)

• †Archaeohyracidae
• †Hegetotheriidae

• Order †Litopterna (Panameriungulata)

• †Protolipternidae
• †Notonychopidae (Notopterna?)
• †Macraucheniidae
• †Adianthidae
• †Proterotheriidae

• Order †Astrapotheria

• †Eoastrapostylopidae
• †Trigonostylopidae (Trigonostylopoidae?)
• †Astrapotheriidae

• Order †Pyrotheria

• †Colombitheriidae
• †Pyrotheriidae

• Order †Xenungulata

• †Carodniidae

References

• Hunter, J.P.; Janis, C.M. (2006). "Spiny Norman in the Garden of Eden? Dispersal and early biogeography of Placentalia". Journal of Mammalian Evolution 13 (2): 89–123. doi:10.1007/s10914-006-9006-6. OCLC 4669969299. 
• McKenna, M.C. (1975). "Toward a phylogenetic classification of the Mammalia". In Luckett, W.P.; Szalay, F.S. Phylogeny of the primates: a multidisciplinary approach (Proceedings of WennerGren Symposium no. 61, Burg Wartenstein, Austria, July 6–14, 1974. New York: Plenum. pp. 21–46. doi:10.1007/978-1-4684-2166-8_2. ISBN 978-1-4684-2168-2. 
• Muizon, C. de; Cifelli, R.L. (2000). "The "condylarths" (archaic Ungulata, Mammalia) from the early Paleocene of Tiupampa (Bolivia): implications on the origin of the South American ungulates". Geodiversitas 22 (1): 47–150. Retrieved May 2013. 
• Rose, Kenneth David (2006). The beginning of the age of mammals. Baltimore: JHU Press. ISBN 0801884721. 
• Shockey, B.J.; Anaya, F. (2004). "Pyrotherium macfaddeni, sp. nov. (late Oligocene, Bolivia) and the pedal morphology of pyrotheres". Journal of Vertebrate Paleontology 24 (2): 481–488. doi:10.1671/2521.