Gondwanatheres have been classified as a group of uncertain affinities or as members of Multituberculata, a major extinct mammalian order.
Another genus known from a single tooth (in this case, a fourth lower premolar), Argentodites, was first described as an unrelated multituberculate, but later identified as possibly related to Ferugliotherium.
Finally, a single tooth from the Paleogene of Peru, LACM 149371, perhaps a last upper molariform, and a recent specimen from Mexico,[1] may represent related animals.
The jaw fragment contains a long tooth socket for the incisor and bears a bladelike fourth lower premolar, resembling those of multituberculates.
Most ferugliotheriids come from the Late Cretaceous epoch (Campanian–Maastrichtian ages, 84–66 million years ago, or mya) of Argentina, where they may have lived in a marshy or seashore environment.
The first member of the family Ferugliotheriidae to be discovered, Ferugliotherium windhauseni, was named in 1986 by Argentinean paleontologist José F. Bonaparte on the basis of a tooth from the Late Cretaceous Los Alamitos Formation of Argentina.
[2] Bonaparte placed Ferugliotherium as the only member of the new family Ferugliotheriidae, which he tentatively assigned to the order Multituberculata, a large group of extinct mammals (distinct from both monotremes and therians, the two major groups of living mammals) that was particularly widespread in the northern continents (Laurasia), but had never previously been found in the south (Gondwana).
Bonaparte considered the gondwanatheres to be probably most closely related to the xenarthrans (sloths, armadillos, and anteaters) within a group called Paratheria.
[2] Together with Bonaparte, he also proposed to classify gondwanatheres as a superfamily (Gondwanatherioidea) within Plagiaulacoidea, including the families Ferugliotheriidae and Sudamericidae.
[10] On the basis of the morphological features of the jaw fragment, they argued that gondwanatheres are not closely related to any other multituberculate group, and consequently placed them in a suborder of their own, Gondwanatheria.
[13] However, in 2009 Yamila Gurovich and Robin Beck identified these fossils as Ferugliotherium and argued in favor of a close relationship between gondwanatheres (including Ferugliotheriidae) and multituberculates.
In 2004, Francisco Goin and colleagues described a single enigmatic tooth from the Paleogene of Peru, LACM 149371; their best estimate was that it represented a member of Ferugliotheriidae.
[15] On the basis of a single p4, Kielan-Jaworowska and colleagues named Argentodites coloniensis, from the Late Cretaceous La Colonia Formation of Argentina, in 2007 as a multituberculate, possibly referable to the suborder Cimolodonta.
[24] The specimen MACN Pv-RN 975, first described by Kielan-Jaworowska and Bonaparte in 1996, may be a jaw fragment of Ferugliotherium, although it has also been identified as an unrelated multituberculate.
[27] The p4 assigned to Argentodites also has eight ridges on both sides, which descend from cusps on the upper margin, and roots at the front and back.
[29] Two other teeth have been identified as upper premolars of Ferugliotherium; as with the jaw fragment, they may also represent an indeterminate multituberculate.
[32] Two heavily worn Ferugliotherium mf1s were originally identified as upper molars of Vucetichia gracilis by Bonaparte in 1990.
[8] On the other hand, overall patterns of cusps and ridges are essentially similar among Ferugliotherium, Gondwanatherium, and Sudamerica, indicating that the three are closely related.
[37] With its low-crowned teeth, Ferugliotherium may have been an insectivore or omnivore, like similar multituberculates such as Mesodma, which is thought to have eaten insects, other arthropods, seeds, and/or nuts.
[51] More recently, a specimen has been found in the Cerro del Pueblo Formation of Mexico, bearing several similarities to Ferugliotherium.