Ansomys, QIU, 1987

Hopkins, Samantha S. B., 2008, Phylogeny and evolutionary history of the Aplodontoidea (Mammalia: Rodentia), Zoological Journal of the Linnean Society 153 (4), pp. 769-838 : 793

ANSOMYS QIU, 1987

Definition: The node group arising from the last common ancestor of Ansomys descendens ( Dehm, 1950) and A. orientalis .

Revised diagnosis: Ansomyines with relatively lophodont dentition, a compressed, blade-like mesostylid, an elongated entoconid, which is widest at the posterolingual end, an anteroposteriorly compressed hypoconulid on the molars, and lacking a large open central basin. Fossettids are well defined, and the enamel of the basins of the lower cheek teeth is slightly rugose in all but Ansomys hepburnensis Hopkins, 2004 .

Referred taxa: See Table 1.

Geographic and stratigraphic range: From the Late Oligocene to the Middle Miocene of Montana and China, in the Late Oligocene of Germany, and in the Middle Miocene of Kazakhstan.

Discussion: The treatment here follows the revision of Ansomys in Hopkins (2004), and is consistent with most of the results of the phylogenetic analysis presented here; if Ansomys proves to be a paraphyletic group as suggested by analysis 5, redefinition of the genus will be necessary.

ALLOMYINAE MARSH, 1877

Definition: The node group arising from the last common ancestor of Parallomys americanus Korth, 1992b and A.nitens .

Revised diagnosis: Small to large, brachydont to hypsodont aplodontids, with relatively lophodont dentition. Accessory crests incipient in most basal members of the clade, becoming more prominent and numerous in the nonmeniscomyine members of the lineage, especially among members of the genus Allomys . Lower molars essentially the same size from M 1 to M 3, but P 4 is slightly enlarged relative to the molars. Entoconid double crested, with one crest directed labially and one directed anterolabially into the centre of the tooth. The basin between the closely positioned metaconid and protoconid of P 4 is narrow and anteroposteriorly elongated, with sharp styles extending down the anterior faces of both metaconid and protoconid. The metaconid of the lower molars is labiolingually compressed, and the hypoconid is anteroposteriorly elongated. A second metaconule is present labially to the one present in all other aplodontoids. This metaconule is small early in the history of the clade, but becomes large later in time. The ectoloph is dominated by crests, not cusps, and is continuous between the paracone and metacone, and closes the central transverse valley. The paracone is positioned more lingually than the metacone. The labial face of M 3 is concave, with a well-formed ectoloph. The mesostyle of P 4 is positioned at the anterior end of the central transverse valley, and is anterolabially directed in the early members of the clade, but is positioned and directed more posteriorly in a few derived Allomys . Although all of these characters diagnose the base of the clade, a few of them, especially the second metaconule and the accessory crests, are lost again among the meniscomyines. Both these features have evolved several times among rodents, and are only useful on a relatively small taxonomic scale.

Referred taxa: See Table 1.

Geographic and stratigraphic range: From the Late Oligocene to recent times of North America, from the Late Oligocene to the Early Miocene of Europe, and from the Early to Late Miocene of Asia.

Stratigraphic range: From the Late Oligocene to the Middle Miocene.

Discussion: This definition roughly follows that of Rensberger (1983), but refers to a monophyletic group. The analysis presented here strongly supports the paraphyly of the traditional allomyine grouping, and of the allomyine genus Parallomys in particular. Thus, all more derived aplodontids are also nested within a monophyletic Allomyinae.