Amphicticeps Matthew and Granger, 1924

TYPE SPECIES: Amphicticeps shackelfordi Matthew and Granger, 1924.

INCLUDED SPECIES: Amphicticeps shackelfordi Matthew and Granger 1924, A. dorog, n.sp., and A. makhchinus, n.sp.

EMENDED DIAGNOSIS: Amphicticeps possesses the following derived characters that distinguish it from basal ursoids and musteloids such as Amphicynodon, Pachycynodon, Cephalogale, Mustelavus, Amphictis, Bavarictis, Pseudobassaris, Mustelictis, and Broiliana: broad and short rostrum, short infraorbital canal, enlarged M1 parastyle, small angle between labial borders of P4 and M1, reduced and lingually positioned M2, reduced m2, and extremely reduced or lost m3. It is primitive compared to Kinometaxia, Paragale, Plesiogale, and other mustelids in its possession of a carnassial notch on P4 and a shallow suprameatal fossa. In contrast to the North American oligobunines, Amphicticeps possesses a postprotocrista on the M1, lacks of a lingual notch on the m1 entoconid crest, and has reduced M2 and m2.

DISTRIBUTION AND AGE: Hsanda Gol Formation, Tsagan Nor Basin, eastern Valley of Lakes, central Mongolian People’s Republic. Early Oligocene (see more comments in Geology and Age under Amphicticeps shackelfordi).

COMMENTS: Ever since its original description, Amphicticeps shackelfordi has remained something of an enigma in its phylogenetic relationships. Offering no formal classification, Matthew and Granger (1924: 4) initially remarked that ‘‘it has the sharply reduced post­carnassial dentition of [stenoplesictoids] with the short, heavy precarnassial dentition of [cynodontoids]. It is not close to any one genus with which I [sic] have made comparisons and might be regarded as a highly progressive miacid rather than as a member of any of the existing families of fissiped Carnivora.’’ Subsequent classifications also reflect this ambiguity; Simpson (1945: 110 and 115) listed it under both ‘‘? Amphicynodontinae incertae sedis ’’ and ‘‘?Stenoplesictinae incertae sedis ’’, whereas Piveteau (1961: 721) considered it as incertae sedis but compared it to Cynodon (5 Amphicynodon). Without suggesting a taxonomic position for the genus, Bonis (1971) commented on its ‘‘parallel’’ resemblance to Harpagophagus, a genus based on a single left M1 and thought to be an amphicyonid.

In the first substantial discussion of Amphicticeps since its original description, Schmidt­Kittler (1981) pointed out the fundamentally arctoid basicranium of Amphicticeps and its musteloid­like molar reduction (transversely elongated M1) and short rostrum. However, he did not consider it a musteloid because of its shallow suprameatal fossa, a character especially emphasized in his analysis of musteloid phylogeny. The form of its M1 seemed to him to be another obstacle to recognizing it as a musteloid. Specifically, he regarded the somewhat swollen buccal border and a ‘‘knoblike’’ (höckerartige) lingual cingulum of the M1 as atypical of a musteloid. He therefore regarded Amphicticeps as a ‘‘basal arctoid’’ prior to the emergence of the musteloid clade. Wolsan (1993) compared its lingually located M2 with those of Potamotherium, but did not draw definite conclusions. Hunt (1996b, 1998c) suggested that Amphicticeps may be an amphicynodontid possibly ancestral to the North American Allocyon and Kolponomos, a suggestion that was followed by Wang and Qiu (2003a).

Among the small carnivorans from the Hsanda Gol Formation, Amphicynodon teilhardi (Matthew and Granger, 1924), founded on a few jaw fragments (see description below), is the only similar­sized arctoid that may potentially be confused with Amphicticeps (other Hsanda Gol carnivorans, such as Stenoplesictis, Palaeogale, and Viverravus, are easily distinguished on the basis of their far more trenchant carnassials that are typical of feliforms; Hunt, 1998b). With the benefit of the more complete materials for both Amphicticeps and Amphicynodon, these two primitive Shand Gol arctoids are contrasted in table 1 to facilitate identification.