What is "meridiungulata"

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 is not known if it is a natural group; it was erected to distinguish the ungulates of South America from other ungulates. Relationships between the orders inside Meridiungulata remain unresolved and it could well be a 'wastebasket' taxon. Most Merdiungulata died out following the invasion of South America by North American ungulates and predators during the Great American Interchange; a few of the largest species of notoungulates and litopterns survived until the end- Pleistocene extinctions.