The Casamayoran age is a period of geologic time (54.0—48.0 Ma) within the Eocene epoch of the Paleogene used more specifically with South American Land Mammal Ages. It follows the Riochican and precedes the Mustersan age.
Several astrapotherian mammals are known from this period, such as Antarctodon and Albertogaudrya from Antarctica and Argentina respectively.
Albertogaudrya and Scaglia were the size of a sheep or a small tapir, hence among the larger mammals in South America at this time.
References
Casamayoran Wikipedia(Text) CC BY-SA