For several decades the affinities of the group were not clear, being first interpreted as early
xenarthrans, or "toothless" mammals similar to the modern
anteater. A variety of studies have placed them as
allotheres related to
multituberculates, possibly even true multituberculates, closer to
cimolodonts than "
plagiaulacidans" are. However, a more recent study recovered them as nested among
haramiyidans, rendering them as non-mammalian cynodonts. A more recently described specimen has since recovered them as allotheres closely related to
multituberculates, but this was soon after followed by a study recovering them as part of
Euharamiyida, which itself was placed inside crown-group Mammalia. There are three known
families within Gondwanatheria. The family Sudamericidae was named by Scillato-Yané and Pascual in 1984, and includes the vast majority of named taxa. The family Ferugliotheriidae was named by
José Bonaparte in 1986, and includes one genus,
Ferugliotherium, and possibly a few other forms like
Trapalcotherium from the Late Cretaceous of South America. Ferugliotheriidae are considered the most basal gondawanatherians, and are sometimes recovered outside the group. The youngest gondwanatherians are known from the
Eocene of South America and Antarctica. The Eocene genus
Groeberia and Miocene genus
Patagonia, two mammals from South America with unusual tooth morphologies usually considered
metatherians, were considered by one paper to be gondwanatheres. However, their conclusions have generally not been accepted. ==Biology==