Genus of extinct mammals from the Late Cretaceous from Argentina
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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jaw fragment have been referred to "Ferugliotherium", but the assignment of many of these is controversial or has been superseded.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.
Taxonomy.
"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.
Description.
"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.
"Ferugliotherium" was much smaller than the sudamericids "Gondwanatherium" and "Sudamerica", and its body mass is estimated to have been about 70 g (2.5 oz). Unlike the hypsodont (high-crowned) sudamericids, "Ferugliotherium" has brachydont (low-crowned) molariform teeth that are supported by at least two roots, not a single massive root. The direction of wear on the teeth indicates that "Ferugliotherium", "Gondwanatherium", and "Sudamerica" all had palinal jaw movement (i.e., the lower jaw moved backwards during the power stroke of chewing)—a feature otherwise only seen in multituberculates among mammals.
Incisors.
Three fragmentary "Ferugliotherium" lower incisors (MACN Pv-RN 701A, 701B, and 701C) are known from the Los Alamitos Formation. Another incisor, MACN Pv-RN 970, was assigned to "Ferugliotherium" by Bonaparte in 1990, but it is much larger than the other three incisors, which are otherwise similar, and probably represents "Gondwanatherium" instead. Only the tips of the three incisors are preserved. They are laterally compressed, with an estimated width of 1.3 mm and height of 2.4 mm in 701A. The medial side (towards the middle of the mouth) is flat, but the lateral side (towards the sides) is convex. There is enamel only on the lower (ventral) side. A large wear facet is present at the tip, forming an angle of about 35° with the ventral margin in 701A. The three incisor fragments are identified as "Ferugliotherium" because of their size and provenance and the presence of a restricted enamel band. They show features, such as lateral compression, an acute angle at the tip, small curvature, and an irregular cross section, that are usually seen in lower, not upper incisors in mammals with procumbent incisors, such as rodents and taeniolabidoid multituberculates.
Four specimens (MACN Pv-RN 702A through 702D) are thought to represent second upper incisors (I2) of "Ferugliotherium". 702A (height 1.5 mm; width 1.1 mm) and 702B are slightly larger than 702C (height 1.2 mm; width 0.9 mm) and 702D. The smaller incisors cannot be lateral incisors (I3), because 702C's wear facet is stronger than would be expected in an I3; therefore, all four upper incisors are identified as central incisors (I2). To explain the size difference, Krause and colleagues suggested that "Ferugliotherium" was variable in size or that the smaller incisors were deciduous precursors of the larger permanent tooth. They considered it less likely that multiple species with similar incisors were present. The upper incisors have enamel only on the dorsal side. The wear facet at the tip is preserved only in 702C, forming an angle of 52° with the dorsal side, and is more concave than the facet in the lower incisors. 702A–D are recognizable as upper incisors because they have a less acute angle at the tip and are less laterally compressed, more curved, and elliptical in cross section.
Incisors of "Ferugliotherium" and "Gondwanatherium" are similar in overall shape and share a restricted band of enamel—a feature otherwise seen only in multituberculates among Mesozoic mammals. The incisors of "Sudamerica" are also similar.
Mandible with lower premolar.
MACN Pv-RN 975, a fragment of the mandible (lower jaw) preserving one premolar, was discovered in 1991 and tentatively identified as "Ferugliotherium" by Kielan-Jaworowska and Bonaparte in 1996, but this assignment remains controversial. The poorly preserved and worn premolar is a bladelike tooth, resembling multituberculate fourth lower premolars (p4). The premolar is 4.8 mm long and bears eight faint ridges on both the labial (towards the lips) and lingual (towards the tongue) sides. On the labial side, the four ridges at the back are more widely separated than the four in front of them. The back and front margins of the tooth are parallel and there is no small cusp on the labial side. There are two roots; the one at the front is larger than the one at the back and bears a furrow. The lower border of the enamel cover is marked by two semicircular extensions of the enamel on the front side, but there is only one such extension at the back. By its size, the number of ridges, and apparently greater length than height, it differs from all known multituberculate first, second, and third lower premolars, indicating that it is a p4.
The dentary (lower jaw bone) itself is robust and short. The length axis of the p4 makes an angle of about 58° with the length axis of the jawbone. The bone is concave on the lingual, but convex on the labial side. There is a diastema (gap) between the p4 and the incisor that would have been in front of it, as in the jaw of "Sudamerica". Gurovich estimated the length of the diastema as 2.5 mm. There is a rounded mental foramen (an opening in the labial side of the jawbone), with a diameter of 0.7 mm, located about 0.8 mm below the dorsal margin of the bone and 1.5 mm in front of the p4. Although the incisor itself is not preserved, its alveolus (the housing of the root) is in part. As in "Sudamerica", it extends far into the dentary, passing below p4. The alveolus is 1.5 mm wide below the front root of p4 and 1.4 mm at the back of the jaw fragment. Although the height of the alveolus cannot be determined because the lower side is broken away, the incisor must have been quite deep.
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