Temporal range: Campanian-Miocene, 70.6–17.5Ma
|Mandible of Sudamerica|
Gondwanatheria is an extinct group of mammals that lived during the Upper Cretaceous through the Miocene in the Southern Hemisphere, including Antarctica. They are known only from isolated teeth, a few lower jaws, two partial skulls and one complete cranium. Because of this fragmentary knowledge their placement is not clear.
The affinities of the group are not clear, but gondwanatherians were first interpreted as early xenarthrans, or "toothless" mammals similar to the modern anteater. This is somewhat ironic, given that they were originally known only from teeth. They were also treated as members of the Multituberculata. The latest thinking is apparently returning towards the xenarthran affinities, or something else entirely. However, a few specimens of Gondwanatherians are reclassified as Multituberculates. Recent studies have confirmed their position as allotheres related to multituberculates.
There are two known families within Gondwanatheria. The family Sudamericidae was named by Scillato-Yané and Pascual in 1984, and includes the genera Sudamerica, Gondwanatherium and Lavanify. The family Ferugliotheriidae was named by José Bonaparte in 1986, and includes one genus, Ferugliotherium.
Further fossils have come from India and Antarctica, where Gondwanatherians once lived in the lush forests of the Eocene. Some South American genera, previously considered to be metatherians, are reassigned to Gondwanatheria: the Eocene genus Groeberia and the Miocene (Colhuehuapian) genus Patagonia.
The fact that Gondwanatherians were present in Antarctica during the Eocene, while the South American varieties became extinct, indicates that the factors that caused their extinction did not affect this continent. Fossils found on Seymour Island of Gondwanatherians (Sudamericidae) show adaptations for a semi-aquatic and perhaps a burrowing way of life, similar to that of living beavers. This suggests an important paleoecological constraint related to dietary preference of this group. Anyway, at the end of the Eocene the climate became unsuitable and most of the flora and fauna of Antarctica became extinct. This includes small, arboreal, fruit and insect-eating possums, 10 kg (22 lb) sloths, middle-to-large sized grazers (sparnotheriodontids and Trigonostylops), falcons and ratites.
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