Ferugliotherium

Ferugliotherium is a genus of fossil mammals in the family Ferugliotheriidae from the Campanian and/or Maastrichtian period (Late Cretaceous; around 70 million years ago) of Argentina. It contains a single species, Ferugliotherium windhauseni, which was first described in 1986. Although originally interpreted on the basis of a single brachydont (low-crowned) molar as a member of Multituberculata, an extinct group of small, rodent-like mammals, it was recognized as related to the hypsodont (high-crowned) Sudamericidae following the discovery of additional material in the early 1990s. After a jaw of the sudamericid Sudamerica was described in 1999, these animals (collectively known as Gondwanatheria) were no longer considered to be multituberculates and a few fossils that were previously considered to be Ferugliotherium were assigned to unspecified multituberculates instead. Since 2005, a relationship between gondwanatheres and multituberculates has again received support. A closely related animal, Trapalcotherium, was described in 2009 on the basis of a single tooth.

About twenty teeth and a jaw fragment have been referred to Ferugliotherium, but the assignment of many of these is controversial or has been superseded. The upper and lower incisors are long and rodent-like and have enamel on only one side of the crown. A fragment of the lower jaw shows that the tooth socket of the lower incisor was very long, extending below the fourth premolar (p4). The p4 is preserved in this fragment. It is blade-shaped and resembles multituberculate p4s. However, the determination of this fossil as Ferugliotherium is in question. The identity of a few additional isolated premolars assigned to Ferugliotherium, some resembling multituberculates, is also uncertain. The first lower molariform (molar-like tooth; mf1) is known from four examples, of which two were originally identified as upper molars of a different species (Vucetichia gracilis), which is now considered a synonym of Ferugliotherium. They bear two longitudinal rows of three or four cusps and transverse crests and furrows. A single example each of the second lower (mf2) and first upper molariform (MF1) show that these teeth also had longitudinal cusp rows and transverse furrows and crests, but the mf2 had only two or perhaps three cusps per row and the MF1 had three longitudinal rows.

Although Ferugliotherium teeth are much lower-crowned than those of the Sudamericidae, they share an essentially similar pattern on the occlusal (chewing) surface of mf1 and mf2, similar incisors, backward jaw movement during chewing, and enamel with small prisms. Ferugliotherium is thought to have been a small animal, with a body mass of about 70 g (2.5 oz), and may have eaten insects and plant material. Its remains have been found in two geological formations of southern Argentina, where it is part of a mammal fauna that also includes the sudamericid Gondwanatherium and a variety of dryolestoids.

Ferugliotherium windhauseni was named in 1986 by Argentinean paleontologist José Bonaparte on the basis of a single second lower molar (m2) from the Late Cretaceous Los Alamitos Formation of Argentina. Both the generic name, Ferugliotherium, and the specific name, windhauseni, honor geologists who studied the geology of Patagonia: Egidio Feruglio and Anselmo Windhausen, respectively. Bonaparte created a new family, Ferugliotheriidae, for the new species and tentatively assigned it to Multituberculata, an extinct group of mammals that was diverse during the late Cretaceous, mostly in the northern continents (Laurasia). In subsequent years, other finds permitted a more confident assignment to Multituberculata. In 1990, Bonaparte described Vucetichia gracilis on the basis of what he interpreted as two upper molars of a relative of Gondwanatherium within the order Gondwanatheria, a small mammalian group that was at the time known only from Argentinean fossils and thought to be related to xenarthrans as part of a now-discarded group called Paratheria. The generic name, Vucetichia, commemorates Argentinean paleontologist Guiomar Vucetich, and the specific name, gracilis (Latin for "slender"), refers to the animal's small size.

However, in 1990 David W. Krause and Bonaparte argued that Gondwanatheria, including Ferugliotherium (family Ferugliotheriidae), Gondwanatherium, and Sudamerica (family Sudamericidae), should be placed within Multituberculata. Two years later, Krause, Bonaparte, and Zofia Kielan-Jaworowska described additional material of Ferugliotherium (which they tentatively placed in the multituberculate suborder Plagiaulacoidea) and suggested that the supposed upper molars of Vucetichia were in fact heavily worn first lower molariforms (mf1) of Ferugliotherium. In 1993, Krause described an unworn mf1 of Ferugliotherium and confirmed that Vucetichia was based on worn specimens of Ferugliotherium and therefore a synonym of the latter. In the same year, he and Bonaparte argued once again that Ferugliotherium, Gondwanatherium, and Sudamerica formed a closely related group of multituberculates, which they called the superfamily Gondwanatherioidea. Kielan-Jaworowska and Bonaparte described a lower jaw fragment with a multituberculate-like lower fourth premolar (p4) from Los Alamitos in 1996 and tentatively identified it as Ferugliotherium. On the basis of the morphological features of the jaw fragment, they argued that gondwanatherians were not closely related to any other multituberculate group, and consequently placed them in a suborder of their own, Gondwanatheria.

In 1999, Rosendo Pascual and colleagues described a jaw of Sudamerica. Because some of this jaw's features were thought to be incompatible with a multituberculate identity, they regarded gondwanatheres (including Ferugliotherium) as Mammalia incertae sedis. However, in 2009 Yamila Gurovich and Robin Beck argued in favor of a close relationship between gondwanatheres (including Ferugliotherium) and multituberculates. The controversy is partially due to disagreement over the assignment of two upper premolars and the jaw fragment described by Kielan-Jaworowska and Bonaparte in 1996; Gurovich and Beck identify these as Ferugliotherium, while Kielan-Jaworowska and others regard them as indeterminate multituberculates.

In the 2000s, some possible close relatives of Ferugliotherium were discovered. An enigmatic tooth from the Paleogene of Peru, LACM 149371, was described in 2004 as possibly related to the family Ferugliotheriidae. Kielan-Jaworowska and colleagues described a p4 from the La Colonia Formation (Late Cretaceous of Argentina) as a new multituberculate genus, Argentodites, in 2007, but Gurovich and Beck noted close similarities between this p4 and the p4 in the possible jaw fragment of Ferugliotherium and suggested that it represented Ferugliotherium or a closely related species. A single mf1 from the Allen Formation (Late Cretaceous of Argentina) was described as another ferugliotheriid genus, Trapalcotherium, in 2009.

Ferugliotherium is known from isolated teeth, the assignment of some of which is controversial. The material from the Los Alamitos Formation, which is mostly in the Museo Argentino de Ciencias Naturales Bernardino Rivadavia (MACN) in Buenos Aires, with one tooth in the Museo de La Plata (MLP) in La Plata, Argentina, has been thoroughly described; while there are additional Ferugliotherium fossils from the La Colonia Formation, they have not been described in detail. Although the fragmentary nature of the known fossils of Ferugliotherium makes it impossible to determine its dental formula with certainty, Gurovich suggested that it had one incisor (possibly two in the upper jaw), no canines, one or two premolars, and two molars on each side of the lower and upper jaws. However, on the basis of comparisons with Sudamerica, which is known to have had four lower molariforms (molar-like teeth, either premolars or molars) in its lower jaw, Pascual and Ortiz-Jaureguizar suggested in 2007 that Ferugliotherium may also have had four lower molars.