Amphicticeps dorog Wang, McKenna, and Dashzeveg, 2005

WANG, XIAOMING, McKENNA, MALCOLM C. & DASHZEVEG, DEMBERELYIN, 2005, Amphicticeps and Amphicynodon (Arctoidea, Carnivora) from Hsanda Gol Formation, Central Mongolia and Phylogeny of Basal Arctoids with Comments on Zoogeography, American Museum Novitates 3483, pp. 1-58 : 22-23

Amphicticeps dorog Wang, McKenna, and Dashzeveg , new species

Figure 8 ; Tables 3, 5

HOLOTYPE: MAE SG.9194, right maxillary fragment with P4–M1 and M2 alveolus.

TYPE LOCALITY: Tsagan Nor Basin, eastern Valley of Lakes, Obor­Khangay Province, Mongolian People’s Republic. Top of Tatal Member, Hsanda Gol Formation, early Oligocene.

REFERRED SPECIMENS: AMNH 21656, left ramal fragment with m2 broken and m3 alveolus, field no. 538; AMNH 21672, left ramal fragment with m1–2, from ‘‘Grand Canyon’’, field no. 531; AMNH 84211, right ramal fragment with m1–2, field no. 532; AMNH 85217, left ramal fragment with m1 and alveoli of p2–4, field no. 538; AMNH 85223, isolated left m1, field no. 538; AMNH 85224, left maxillary fragment with P3, field no. 538; AMNH 85233, isolated left m1, field no. 538; MAE SG.91.9192, left ramal fragment with c broken and p2–4, from locality MAE 91–82, Tatal Gol, below lava in Tatal Member; MAE SG.95.8655, left ramus fragment with p3; MAE SG.97.3576, isolated right m1; and MAE SG.9799, left maxillar fragment with M1.

ETYMOLOGY: Mongolian: dorog , badger.

DIAGNOSIS: Amphicticeps dorog differs from A. shackelfordi in its possession of the following derived characters: larger size and more robust dentitions and jaws, lower and more crestlike P4 protocone, more prominent P4 anterior cingulum, more reduced M1 parastyle, relatively larger and more labially located M2, relatively shorter m2, and loss of m3. It is readily distinguishable from A. makhchinus in its smaller size, less lingually and posteriorly expanded P4 protocone crest, more labially oriented M1 postprotocrista, and less lingually expanded lingual cingulum of M1.

DESCRIPTION: Our knowledge of this new species is still limited to isolated maxillar and mandibular fragments and cheek teeth.

Upper teeth (figs. 8A, C): Only a single isolated P3 ( AMNH 85224 ) is available and it has a simple main cusp and a well­developed cingulum. The P 4 on the holotype is relatively wide due to a rather lingually expanded protocone. The protocone is low and its apex is located along the lingual margin and is continuous with the lingual cingulum through crests on either sides of the cusp. There is also a low ridge on the labial side of the protocone that ends at the base of the paracone. A cingulum is strongly developed around the entire P4, and the anterior cingulum is especially strong to the point of almost forming a parastyle. The labial cingulum is better developed than the lingual cingulum. The paracone is broad based and has a distinct anterior ridge leading down from the apex to the base. There is a welldeveloped carnassial notch .

The most distinguishing feature of the M1 is its transverse elongation, mostly due to a large paracone and parastyle. The paracone is the tallest cusp of the tooth, and is substantially larger and taller than the metacone. A large parastyle is formed by a prominent elevation of the labial cingulum surrounding the paracone. In contrast, the labial cingulum around the metacone is much narrower and lower. The metacone is on the posterolingual aspect of the paracone. The protocone is about the same height as the metacone. A distinct pre­ and postprotocrista converge at the apex of the protocone and form a sharp V­shaped crest. No protoconule or metaconule is present. The lingual cingulum surrounds the protocone but is asymmetrical— its posterolingual corner behind the protocone is more swollen than its anterolingual corner.

No M2 is preserved. The double­rooted alveoli on the holotype suggest an M2 that is probably transversely elongated, as is M1, but probably anteroposteriorly short because of a short m2 and the absence of an m3 (see below). The location of the labial root indicates an M2 that is not lingually shifted as in Amphicticeps shackelfordi .

Lower teeth (figs. 8B, D, E, F): Although no associated upper and lower jaws are available, our references of isolated lower jaws are mostly based on their intermediate sizes, corresponding to size differences of upper teeth of different species of Amphicticeps , and on their dental morphologies that are consistent with those of the upper teeth. Fragmentary lower jaws, such as in AMNH 21672, indicate a robust mandible of deep and thick horizontal ramus.

Lower premolars are best preserved in MAE SG.91.9192, which has p2–4. Both p2 and p3 are similar, with a simple main cusp and an indistinct anterior cingular cusp, although the latter is larger and less asymmetrical in lateral view. A narrow cingulum surrounds much of the crown of these premolars. The p4 has added a moderate posterior accessory cusp as well as a posterior cingular cusp. Its anterior cingular cusp is also better developed than those of anterior premolars. The p4 cingulum also becomes more distinct.

The m1 trigonid is relatively short and its shearing blade bends lingually. The protoconid is the largest and tallest cusp. The metaconid and paraconid are of approximately the same height. The metaconid is lingual to, and slightly posterior to, the protoconid. The labial cingulum is narrow, and a short and indistinct lingual cingulum is present between the paraconid and metaconid. The tall trigonid is in contrast to a low talonid, which is dominated by a large (at the base), but relatively low hypoconid. The hypoconid is crestlike. It is rather labially located at its posterior end and stops anteriorly at the base of the protoconid, almost directly below the apex of the protoconid. The entoconid is no more than a low crest, directed posteriorly at an angle with the long axis of the tooth. The entoconid crest is decorated with fine wrinkles along its top edge. An indistinct labial cingulum surrounds the talonid but no cingulum is present on the lingual side.

The m2 is single rooted, very short, and almost equal in its length and width. The trigonid is formed by two low cusps, the protoconid and metaconid, which are set apart from each other. The two cusps are located almost on the lingual and labial borders of the tooth. A hypoconid is barely distinguishable on the talonid. A vague cingulum is developed on the anterior half of the tooth. The m3 is absent.

COMPARISON: Even on the basis of the fragmentary materials at hand, the transitional nature of this species seems readily apparent— Amphicticeps dorog is in many ways an intermediate form between the more primitive A. shackelfordi and more derived A. makhchinus . Average length of the upper carnassials is 15% longer than that of A. shackelfordi but 16% shorter than that of A. makhchinus . In the lower carnassial length, A. dorog is 22% longer than that of A. shackelfordi . Such size differences are comparable to those among modern sympatric species of some desert canids ( Dayan et al., 1989, 1992), which offer a quantitative criterion for identification of fragmentary materials. These overall size differences, in addition to the fact that the two species cluster by themselves without intermediate individuals to bridge the gap, strongly suggests a separate species for A. dorog .

Qualitative morphological differences also indicate a transitional form for Amphicticeps dorog . In the following characters A. dorog is almost exactly intermediate between A. shackelfordi and A. makhchinus : the crestlike P4 protocone, the development of the P4 anterior cingulum, the size of the M1 parastyle, the development of the posterior lingual cingulum of M1, and the angle between the labial borders of the P4 and M1.

Figures

Fig. 8. Amphicticeps dorog, n.sp. A, lateral view of upper teeth, MAE SG.9194, holotype; B, lateral view of anterior ramal fragment, MAE SG.91.9192; C, occlusal view of upper teeth, MAE SG.9194, holotype, stereophotos; D, occlusal (stereophoto), E, lingual, F, labial views of lower jaw fragment, AMNH 21672. Scales 5 10 mm; top scale is for B, middle scale for A, C–D, and lower scale for E and F.