Description
Ferugliotheriids are known from a few dozen isolated teeth and a questionably allocated jaw fragment. Most fossils are referred to Ferugliotherium; Trapalcotherium and Argentodites were each described on the basis of a single tooth. Their precise dental formula is unknown, but incisors, premolars, and molariform teeth have been identified. Gurovich suggested that Ferugliotherium 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.
Unlike the very high-crowned (hypsodont) sudamericids, ferugliotheriid teeth were low-crowned (brachydont). Furthermore, sudamericid molariforms tend to be larger and are supported by one large root, but the smaller ferugliotheriids have at least two roots under their molariforms. Ferugliotherium is estimated to have weighed 70 g (2.5 oz).
The incisors, known only from Ferugliotherium, are procumbent and long. Three lower and four upper incisors are known. As is usual in mammals with similarly shaped (gliriform) incisors, the lower incisors are more laterally compressed, are less curved, form a greater angle between the front side and the wear facet at the tip, and are less elliptical in shape than the uppers. The enamel band is restricted to the side that faces the lips in both the lower and upper incisors (the lower side in the lowers and the upper side in the uppers).
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. The fossil preserves a bladelike premolar, identified as the fourth premolar, and the piece of the jawbone below it. A diastema (gap) is present between the premolar and the incisor that would have been located in front of it. The alveolus (socket) of the lower incisor extends all the way through the fossil. The p4 bears eight ridges on both sides of the longitudinal crest and is supported by two roots at the front and back. 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. According to Kielan-Jaworowska and colleagues, it differs from that of MACN Pv-RN 975 in its rounded, as opposed to angular shape. However, Gurovich and Beck attribute this difference to the fact that the latter has undergone much more wear.
Two fossils have been interpreted as isolated lower premolars of Ferugliotherium; however, neither is still regarded as such. Two other teeth have been identified as upper premolars of Ferugliotherium; as with the jaw fragment, they may also represent an indeterminate multituberculate. One of the two preserves two longitudinal rows of cusps, of which one contains four and the other at least two cusps. The other is more poorly preserved, but may represent the same tooth position. These teeth resemble multituberculate upper premolars.
Four putative first lower molariforms (mf1s) of Ferugliotherium are known, and the only known tooth of Trapalcotherium is also thought to be an mf1. Ferugliotherium mf1s are roughly rectangular, with rounded corners, and bear two longitudinal rows of cusps. There are four cusps in the lingual row (on the side of the tongue) and three in the labial row (the side of the lips). The cusps are connected to cusps in the other row by transverse ridges and separated from cusps in their own rows by three transverse furrows. Two heavily worn Ferugliotherium mf1s were originally identified as upper molars of Vucetichia gracilis by Bonaparte in 1990. One of the two preserves the roots; at the front and back, there were two roots, fused at their bases. The mf1 of Trapalcotherium differs only in some details; among others, the cusps are less distinct from the crests. The sole mf2 of Ferugliotherium is the holotype. It bears two rows of two cusps. The cusps in the front and back pairs are connected by a broad ridge and the two pairs are separated by a deep furrow. Transverse ridges between the cusps similar to those seen in ferugliotheriids are not known in any multituberculate. 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.
One Ferugliotherium tooth is thought to be a first upper molariform (MF1). It is almost rectangular and bears three longitudinal rows of cusps. There are five cusps in the middle row, which is oriented obliquely, four cusps in one of the rows on the side of the tooth, and two or three in the other row on the side. As in the lower molariforms, the cusps are connected by transverse ridges and separated by furrows. LACM 149371, the enigmatic possibly ferugliotheriid tooth from Peru, is a triangular tooth bearing six or seven cusps, which are connected by crests and surround two deep fossae (basins) and a third shallower fossa.
Read more about this topic: Ferugliotheriidae
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