Draft:Megapeomys

Megapeomys Temporal range:
Jaw and teeth of Apeomyoides savagei, the closest known relative of Megapeomys, in stereopairs. A, holotype lower jaw (A1: labial view of jaw, A2: labial view of cheek teeth, A3: lingual view of cheek teeth). B, left first or second upper molar (B1: labial view, B2: lingual view). C, left deciduous fourth upper premolar (C1: labial view, C2: lingual view).
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	†Eomyidae
Subfamily:	†Apeomyinae
Genus:	†Megapeomys Fejfar, Rummel & Tomida, 1998
Type species
†Megapeomys lavocati Fejfar et al., 1998
Species
†M. bobwilsoni Korth and Morea, 2002 †M. lavocati Fejfar et al., 1998 †M. lindsayi Fejfar et al., 1998 †M. repenningi Yukimitsu Tomida, 2011

Megapeomys(meaning "large Eomyid") is a genus of relatively large Eomyids(extinct family of rodents, related to present-day pocket gophers and kangaroo rats) from the Early Miocene in Eurasia and from the Barstovian in the western United States.

The genus was first described in 1998 by Oldřich Fejfar, Michael Rummel and Yukimitsu Tomida, with the type species, M. lavocati, from a mandible found in the North Bohemian brown coal basin in the Czech Republic and karstic sites in the south of Germany.

Taxonomy and ecology

The subfamily Apeomyinae is thought to have been widespread in the Early Miocene but are today not common as fossils. They can be distinguished from other Eomyids by their dentition and their size, commonly being larger than other Eomyids. Some research also suggests that Apeomyines favoured a drier environment, separating them further from other Eomyids when it comes to ecology.

There has been some discussion on the taxonomy of the Apeomyinae group, originally it was classified as a subfamily of the Eomyidae family but in 2008 the group was described as a tribe, Apeomyini, belonging to the subfamily Eomyinae.

Four different species have been described as belonging to the Megapeomys genus. They are: M. bobwilsoni(discovered in Nevada), M. lavocati(discovered in the North Bohemian basin), M. lindsayi(discovered in the North Bohemian basin) and M. repenningi(discovered in central Japan). The species are named in honour of four scientist; Robert W. Wilson(M. bobwilsoni), René Lavocat(M. lavocati), Everett H. Lindsay(M. Lindsayi) and Charles A. Repenning(M. repenningi) for their great contributions to the study of palaeontology.

Description

Megapeomys was a relatively big Eomyid with high-crowned cheek teeth and a wide space between the incisors and cheek teeth, which is typical of Apeomyines. Additionally, the molars and premolars have two separate lobes and resemble a bilophodont structure, indicating a close relationship to an older, ancestral genus Apeomys. In spite of that the genus shows relatively fast evolution, including morphological changes in the dentition and shape of mandible.

The mandible of the Megapeomys displays an especially long and narrow rostral part and diastema in comparison with Eomys zitteli(an Eomyid species belonging to the genus Eomys). A longer and narrower rostral part and longer diastema is also seen in the mandibles of Apeomys tuerkheimae(an Eomyd species also belonging to the Apeomyinae subfamily). The long lower jaw of Apeomys and Megapeomys indicates that their scull had a longer rostrum(as observed in the skull remains of Apeomys tuerkheimae).

The cheek teeth's rectangular shape is one of the other characteristics that set Apeomyoides apart from other Apeomyines. The lower molars have three roots, while the fourth lower premolar has two and is bigger than the molars behind it.

One characteristic that sets M. lindsayi apart from all other Apeomyinae, perhaps with the exception of M. lavocati, whose teeth are unknown, is the development of a totally bi-lobed tooth pattern also in the upper dentition. If future research discovers that M. lavocati shares this trait with M. Lindsayi, it might indicate that Megapeomys is a distinct Eurasian lineage, and that M. bobwilsoni could represent a different, North American, genus.