Tillodontia is an extinct suborder of
eutherian mammals known from the
Early Paleocene to
Late Eocene of China, the
Late Paleocene to
Middle Eocene of North America where they display their maximum species diversity, the
Middle Eocene of
Pakistan, and the Early Eocene of
Europe. Leaving no descendants, they are most closely related to the
pantodonts, another extinct group. The tillodonts were medium- to large-sized animals that probably feed on roots and tubers in temperate to subtropical habitats.[1]
Description
Tillodonts had rodent-like incisors, clawed feet and blunt, cusped teeth. They were mostly medium-sized animals, although the largest of them (such as Trogosus) could reach the size of a large bear.[2]
The cranium ranged in length from 5 to 37 cm (2.0 to 14.6 in) and had a characteristic elongated
rostrum, an elongated
mandibular symphysis, and a shortened basicranial region. The second upper and lower incisors are large in most species, the first upper and lower premolars are small or absent, the fourth upper and lower premolars are molariform (molar-like).[1]
When
Marsh first named and described the tillodonts, he explained:[3]
These animals are among the most remarkable yet discovered in American strata, and seem to combine characters of several distinct groups, viz: Carnivores, Ungulates, and Rodents. In Tillotherium Marsh [=Trogosus], the type [specimen] of the order, the skull has the same general form as in the Bears, but its structure resembles that of Ungulates. The molar teeth are of the ungulate type, the canines are small, and in each jaw there is a pair of large scalpriform incisors faced with enamel, and growing from persistent pulps, as in Rodents.
When naming his new "
pachyderm" species Trogosus castoridens ("beaver-toothed gnawing-hog"), Leidy added that it was a fossil "which would appear to have pertained to the stock from which diverged the Rhinoceros and Mastodon, the Peccary, and perhaps the Beaver."[4]
Classification
Franchaius from the early Eocene of Europe, Benaius, Lofochaius, Meiostylodon, and Huananius from the early Paleocene of China, and Yuesthonyx from the late Paleocene of China are primitive forms. Interogale from the late Paleocene of China, and Anchilestes probably from the middle Paleocene of China, were once assigned to
Anagalida, but may also be primitive tillodonts.[5]
The monophyly of the subfamily
Trogosinae is unchallenged, but
Esthonychines most likely includes the ancestors of Trogosinae and therefore is probably paraphyletic. Tillodontia is mostly known from dentaries and teeth. The cranium is best known from Trogosinae and the postcranium from Trogosus.[6]
Azygonyx and Esthonyx from North America, Franchaius and Plesiesthonyx from Europe, and Basalina from Pakistan are all morphologically closely related but obviously geographically quite widespread. In contrast, Asian tillodonts tend to be smaller and less derived. This possible link between specimens from Pakistan and Europe with those from North America adds evidence to a faunal interchange between these continents during the early Eocene.[7]
Baudry, Mylène (1992). "Les Tillodontes (Mammalia) de l'Eocène inférieur de France". Bulletin du Muséum National d'Histoire Naturelle, Section C. 14 (2): 205–243.
Dehm, Richard; Oettingen-Spielberg, Therese zu (1958). Paläontologische und geologische Untersuchungen im Tertiär von Pakistan. 2. Die mitteleocänen Säugetiere von Ganda Kas bei Basal in Nordwest-Pakistan. Abhandlungen / Neue Folge, 91. Munich: Beck.
OCLC163296508.