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 post-carnassial 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 (= 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, Schmidt-Kittler (1981) pointed out the fundamentally arctoid basicranium of Amphicticeps and its musteloid-like 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 similar-sized 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.

Holotype:

AMNH 19010, nearly complete skull with left and right P1–2, P4–M1, and alveoli of left and right C1, P3, and M2 (Matthew and Granger, 1924: figs. 4–5).

Type Locality:

Originally designated as from “Hsanda Gol formation, Loh” (Matthew and Granger, 1924: 4), AMNH 19010 (field no. 89) was collected from about 2 mi southwest of the Loh campsite, in Tsagan Nor Basin, eastern Valley of Lakes, Obor-Khangay Province, in north-central Mongolia.

Referred Specimens:

AMNH 19017, partial left ramus with p2–m1 and alveoli of c1– p1 and m2, field no. 69, from Loh; AMNH 19127, partial right ramus with p3, m1, and alveoli of c1–p2, p4, and m2, field no. 84, from Loh; AMNH 19128, right ramal fragment with m1 and alveoli of c1–p4 and m2, field no. 92, from 2 mi southwest of Loh; AMNH 21695, left ramal fragment with m1 and alveoli of c1–p4, field no. 536, from 2 mi west of the “Grand Canyon” area, which is 10 mi west of Loh; AMNH 83610, left ramal fragment with p4–m2 and m3 alveolus, field no. 531, “Grand Canyon”; AMNH 81336, left ramal fragment with m2 and m3 alveolus; AMNH 85749, right ramal fragment with m2–3, field no. 548; MAE BU.91.9187–90 (AMNH cast 129686), partial rostrum with right alveoli of C1–P2, right P3–M2, and left P3–M1, partial mandible with left p2, p4–m2, and alveoli of c1–p1 and p3, and right p1–m2 and root of m3, collected by Perlé Altangerel in 1994, field no. M-152, from 2 mi southwest of Loh; MAE SG.95.7518, right ramal fragment with p2, p4, and m1 (broken); MAE SG.95.8919, posterior skull fragments with top of the inion and left basicranial region, 45°17′49″N 101°37′13″E, collected by Khosbayar on 10 August 1995; and MAE M-217, isolated left m1, field no. M-217, from 2 mi southwest of Loh.

Distribution:

Early Oligocene of north-central Mongolia. An undescribed record was mentioned in the early Oligocene Khatan-Khayrkhan locality of Altai Province of Mongolia by Russell and Zhai (1987: 324).

Geology and Age:

The above referred specimens of Amphicticeps shackelfordi come from three localities (some specimens lack a detailed locality record): (1) general vicinity of Loh for AMNH 19017 and 19127; (2) 2 mi southwest of Loh for AMNH 19010, AMNH 19128, MAE BU.91.9187–90, and MAE M-217; (3) general vicinity or 2 mi west of the Ulaan Khongil (“Grand Canyon” or Tatal Gol) for AMNH 21695 and 83610.

While field studies are currently pursued by the on-going joint expeditions of the MAE and formal stratigraphic revisions will have to wait for that result (see Höck et al., 1999, for a recent summary), it is relevant to note here that the above three Amphicticeps-producing localities fall within a more restricted concept of the Hsanda Gol Formation close to the level of a discontinuous but approximately contemporary basaltic lava (Basalt I of Höck et al., 1999).

Historic collections are largely concentrated in the Ulaan Khongil fauna in the lower part of the Hsanda Gol Formation below the prominent basaltic lava and immediately above. Amphicticeps specimens from near the Loh campsite and 2 mi southwest of Loh (including the holotype) are darkly stained due to the percolation of ground water, and they all belong to the Ulaan Khongil fauna. AMNH 21695 and 83610 from near the “Grand Canyon” area, on the other hand, are light-colored and may belong to the Zavlia fauna in the upper part of the Hsanda Gol Formation above the lava. This presumed younger age of AMNH 21695 and 83610 relative to the rest of the A. shackelfordi hypodigm is also consistent with the former's wider m1 and more prominent lingual cingulum on the m1 trigonid, tendencies that indicate a slightly more advanced stage of evolution for the species.

Emended Diagnosis:

Amphicticeps shackelfordi is distinguishable from the more derived A. makhchinus and A. dorog by its smaller size, smaller angle between the labial borders of P4 and M1, more enlarged M1 parastyle, larger M1 metaconule, more reduced anterior cingulum of M1, and more lingually located M2. In addition, the P4 protocone of A. shackelfordi is larger than in A. dorog, but is less well developed than in A. makhchinus.

Description:

Matthew and Granger's (1924) original report of Amphicticeps shackelfordi consisted of a brief diagnosis only. A full description is furnished here for the holotype and the newly referred materials.

Skull (figs. 2–4): The holotype, AMNH 19010, is still the only nearly complete skull available, although additional referred cranial fragments supplement the holotype in a number of important ways. Its rostral part is slightly crushed, such that the left cheek region is uplifted by approximately 3 mm. The reconstructed skull illustrated by Matthew and Granger (1924: fig. 5) is mostly accurate in overall proportions except for a more posteriorly displaced mastoid process (relative to the nuchal crest) in the dorsal view.

For a small carnivoran, the skull is rather strongly built, with a short and broad rostrum. The incisor-bearing part of the premaxillary is broken off and only the posterior processes of the premaxillary between the nasal and maxillary are preserved; they extend slightly behind the level of the P2. The posterior tip of the nasal reaches nearly to the level of the postorbital process of the frontal. In keeping with the broad snout, the frontal shield is also wide, that is, there is a long distance between upper rims of the orbits. There is a small fossa above the antorbital rim on the frontal/maxillary suture, for the insertion of the levator nasolabialis, and this fossa is more prominent on the right side of the holotype. The postorbital process of the frontal is small but rather sharply pointed; that on MAE BU.91.9187–90 is more reduced. The distance between the postorbital constriction and the postorbital process is relatively elongated (the postorbital constriction is disjointed in the type but enough is preserved on the right side to indicate this elongation), and is approximately 12 mm, as is also seen in Potamotherium and Paragale. The temporal crests merge into the sagittal crest slightly behind the postorbital constriction. The braincase is not laterally expanded near the postorbital constriction as in Potamotherium or nearly becoming so in Paragale. Although not very high, the sagittal crest is thick and robust; so is the nuchal crest. The temporal region of the skull has a rugose surface texture. In lateral view, the skull is somewhat shallow and has a rather flat forehead.

The anterior half of the right orbital region is well preserved on MAE BU.91.9187–90 (fig. 4). The infraorbital canal is short, about 3 mm long, and has a round cross section. Immediately above the canal is a small, rounded lacrimal bone forming the inner rim of the antorbital rim. The lacrimal foramen on the lacrimal bone opens posterodorsally. About 1 mm into the orifice for the lacrimal sac, there is a small foramen on the ventral floor that opens into the dorsal wall of the infraorbital canal. A slender process of the palatine meets the lacrimal and excludes orbital contact of the frontal with the maxillary. At the palatine–maxillary–lacrimal junction, there is a small, oval fenestra, probably due to lack of ossification at this stage of the ontogeny, although a fossa for inferior oblique muscle in hyaenids has been identified at the same triple junction (Werdelin and Solounias, 1991: fig. 26). The anterior process of the jugal is broken away in both AMNH 19010 and MAE BU.91.9187–90, leaving the jugal-maxillary suture surface well exposed in both specimens. From these sutures, it can be deduced that the anterior tip of the jugal stops just above the infraorbital canal and does not reach the lacrimal bone.

Basicranium (fig. 5): The occipital condyles are broken off on both sides of the holotype. The remaining basioccipital floor between the bullae is distinctly widened posteriorly, such that the lateral edges of the basioccipital form a 25° angle, in contrast to smaller angles in primitive arctoids such as Amphictis and to nearly parallel (0°) edges in canids. A small, rounded process for the attachment of the rectus capitis ventralis muscle lies close to the lateral edges of the basioccipital and is slightly in front of the posterior lacerate foramen. Both glenoid fossae are missing. On the left side, however, the medial segment of the postglenoid process is still preserved. Behind this broken process is a small postglenoid foramen, 1 mm in diameter.

The mastoid part of the petrosal is inflated, forming a prominent, laterally protruding mastoid process. The process has a smooth and flat lateral facet and is connected to the paroccipital process via a posterior ridge and to the lambdoidal crest via a more prominent dorsal blade. Such a blade can also be seen in most North American oligobunines. The mastoid tubercle (processus hyoideus) is formed by the petrosal. The posteriorly directed paroccipital process is broadly based because of its expanded wings on each side, but shows no sign of fusion with the bulla (not preserved) at the base. There is a low, longitudinally oriented ridge on the ventral surface of the paroccipital process.

In front of the mastoid process is an oval-shaped suprameatal fossa; its long axis is transversely oriented. The fossa is not fully enclosed toward the medial side, and is thus incompletely rimmed. Approximately 1.5 mm deep, the fossa is excavated into the squamosal bone, which forms the anterior wall of the mastoid process. The suprameatal fossa is primarily developed toward the caudal direction, and is excavated slightly toward the ventrolateral aspect such that it begins to be hidden by a thin bony rim, although the degree of excavation is far less than seen in some procyonids and mustelids.

Although both bullae are missing, the presence of an ectotympanic bulla is indicated by a clearly defined scar posterior to the postglenoid foramen and by a broad, smooth depression on the alisphenoid/squamosal suture (fused) area just medial to the postglenoid process. Such surface markings leave little doubt as to where the anterior crus of the ectotympanic ring was attached (also see the description under Amphicticeps dorog for the preserved ectotympanic). A broad facet facing anteroventrally between the posterior lacerate and stylomastoid foramina at the base of the paroccipital process is apparently the site of attachment of the posterior crus of the ectotympanic. The presence of an entotympanic, on the other hand, is indicated by a 2-mm-wide rugose area on the ventral surface of the promontorium immediately lateral to the petrosal/basioccipital juncture. It is not possible to ascertain whether a bony external auditory meatus was present. However, the rather distinct mark of the above mentioned ectotympanic attachment behind the postglenoid foramen suggests that the anterior crus of the ectotympanic does not wrap around to superimpose on the squamosal around the dorsal bony passage of the meatus to form a complete ring by the ectotympanic, as happens in many arctoids that have a tubular external bony auditory meatus.

The promontorium of the petrosal is prominently domed ventrally, particularly near the fenestra cochleae and fenestra vestibuli (oval and round windows). Its ventral surface is marked by at least two indistinct grooves (more clearly shown on the left side) that begin posteriorly at a small tubercle near the entotympanic/promontorium contact facet. These grooves make small arches laterally at a level slightly in front of the fenestra cochleae and then turn medially toward the entotympanic/promontorium suture. Despite the superficial resemblance of the course of these grooves to the sulcus of the promontorial branch of the internal carotid artery and nerve in primitive caniforms (Wang and Tedford, 1994), its occupant is unlikely to be a promontorial artery, contrary to Cirot (1992: fig. 2), who postulated a promontorial artery in the primitive musteloid Amphictis, and to Schmidt-Kittler (1981), who implied the existence of an internal carotid artery on the promontorium of Amphicticeps. In taxa with a promontorial artery, there is usually a stapedial branch leading transversely toward the oval window. In Amphicticeps there is no such transverse sulcus medial to the oval window. Instead, there is a distinct groove along the ventral rim of the oval window. Such a longitudinal groove can also be found in Promartes and in living procyonids. In the case of the latter group, the soft structures that left the grooves are fine branches of the caroticotympanic artery and the accompanying caroticotympanic nerves (Story, 1951: fig. 83). The caroticotympanic artery, which is a minor component in the internal carotid artery, arises from the main internal carotid artery within the carotid canal, and after looping across the promontory, anastomoses with the tympanic arteries. The inferior tympanic artery and the tympanic nerve loop around the posterior edge of the round window instead the anterior position as in a promontory artery. The surface sulci on the promontorium of Amphicticeps are thus best reconstructed as left by an arterial and nervous configuration similar to that of extant procyonids, that is, no promontory artery is present. The main course of the internal carotid artery is assumed to be in the typical arctoid fashion enclosed within the medial bullar wall (see the description under A. teilhardi for further evidence of a medially positioned internal carotid artery).

At the posteromedial corner of the promontorium, there is a distinct posterior process protruding toward the posterior lacerate foramen. This process is broken off on the left side, showing pneumatic spaces beneath the bony surface.

The fossa for the tensor tympani is deep and located anteromedial to the epitympanic recess. There is a thin sheet of bone covering the canal for the facial nerve; some segments of this sheet are so thin that the bone is rather transparent along the nerve canal. The epitympanic recess is shallow, and walled by squamosal ventrolaterally and petrosal dorsolaterally.

Medial to the Eustachian canal at the level of the presumed anterior end of the entotympanic, the basisphenoid is deeply excavated into a large pit just anterior to the median lacerate foramen. This space marks the turnaround point of the internal carotid artery (cica of fig. 5; Wang and Tedford, 1994). The inferior petrosal vein is excavated into the lateral wall of the basioccipital but remains rather thin (approximately 1 mm in diameter) within a canal formed by the petrosal and basioccipital (ips of fig. 5; best seen near the posterior lacerate foramen). The caliber of the inferior petrosal vein is such that it is unlikely to be able to accommodate a double-looped internal carotid artery hypothesized to be present in many ursoids (Hunt, 1977; Hunt and Barnes, 1994).

The area anterior to the Eustachian canal is damaged on both sides of the skull, and it is not possible to ascertain the status of the alisphenoid canal except by indirect inferences. Schmidt-Kittler (1981: 784) stated, without elaboration, that Amphicticeps has an alisphenoid canal on each side of the skull. On AMNH 19010, only the anterodorsal roof of the foramen rotundum (shared with the anterior opening of the alisphenoid canal) is partially preserved on each side of the skull, and the ventral floor of the canal (if present) is missing. Further preparation on the better preserved left side of the holotype reveals a short segment of bone, about 2 mm in length, between the posterior aspect of the foramen rotundum and the foramen ovale. In Canis (Evans and Christensen, 1979) and Ailurus (Story, 1951), the maxillary artery enters the posterior opening of the alisphenoid canal (caudal alar foramen in Evans and Christensen, 1979) and emerges from the foramen rotundum (rostral alar foramen). In Procyon (which lacks the alisphenoid canal), on the other hand, only a small branch of the internal maxillary artery, the medial meningeal artery, enters the foramen ovale (Story, 1951: fig. 82). On AMNH 19010, the bony bridge flooring the orbital fissure and roofing the alisphenoid canal forms a half-pipe structure on the ventral view, possibly because of a broken ventral floor for the alisphenoid canal. A tiny foramen is present on the medial wall of the alisphenoid canal at the level of the presumed posterior entrance of the canal, as is also seen in Amphicynodon teilhardi. While structural damages do not permit us to state with certainty the existence of a posterior opening of the alisphenoid canal, we agree with Schmidt-Kittler that an alisphenoid canal is likely present.

Bulla of MAE SG.95.8919 (fig. 6): We tentatively refer a left bulla and associated posterior-most portion of the skull, MAE SG.95.8919, to Amphicticeps shackelfordi. Although the bullar size and overall basicranial morphology seems to be compatible with the holotype, there are a number of differences that prevent us from being certain of our reference. Furthermore, in the absence of associated dental materials in MAE SG.95.8919, it is prudent to describe this bulla separately in order to highlight the conflicting morphologies in the basicranial area from those in the holotype.

MAE SG.95.8919 consists of a crushed posterolateral aspect of the skull, preserving much of the left bulla as well as the occipital condyles and the top of the skull. Although much of the bony relationships between various elements are intact, crushing has distorted some areas so that full restoration of their original relationships is no longer possible.

The top of the braincase is well preserved, including about 25 mm of the posterior-most segment of the sagittal crest and a complete nuchal crest. The sagittal crest is 7 mm high at its deepest point just in front of the nuchal crest. The posterior segment of the sagittal crest on the holotype is missing, but based on the height of its nuchal crest, seems to be slightly lower than that in MAE SG.95.8919. The temporal foramen at the suture of parietal and supraoccipital is more posteriorly located than in the holotype. The profile of the nuchal crest, viewed from the caudal end, is also different from that of the holotype; instead of a rather flat top in the holotype, MAE SG.95.8919 has a rather pointed inion with a more steeply sloped nuchal crest on either side. The nuchal crest is also slightly thinner than in the holotype.

The most prominent difference between MAE SG.95.8919 and the holotype is in the size and lateral extrusion of the mastoid processes, although the overall construction of the mastoid process in MAE SG.95.8919 is similar to that in the holotype. A laterally expanded mastoid forms a conspicuous, rounded (in dorsal view) crest continuous from the lambdoidal crest. In lateral view, the outline of the mastoid process is roughly triangular. A posteroventral facet for attachment of the obliquus capitis cranialis muscle (Antón et al., 2004) is the largest surface of the process, and this facet is less posteriorly oriented than in the holotype. The depth of the mastoid process in MAE SG.95.8919 is also significantly less than in the holotype, resulting in a smaller area of the lateral facet of the mastoid for attachment of the sternomastoideus muscle. Overall, one gets the impression that the much enlarged and laterally extruded mastoid process in the holotype is mostly related to the increased size and leverage of the m. obliquus capitis cranialis, and thus presumed more powerful head rotation (Antón et al., 2004), although ontogenetic variation may also be responsible for such differences.

Associated with its smaller mastoid process, the paroccipital process in MAE SG.95.8919 is also narrower in ventral view—the broader process in the holotype is apparently the result of a proportional lateral expansion due to its greatly expanded mastoid process. Otherwise, the paroccipital process is of the same general construction, with a dorsally convex and ventrally flat process that is completely posteriorly oriented without any hint of a ventral bending toward the bulla. Such a “free” paroccipital process, without hugging the bulla, is often a primitive condition for all caniforms (e.g., see Wang, 1994; Wang and Tedford, 1994; Wang et al., 1999).

The bulla is more or less intact with the exception of a crack on the ventrolateral aspect. The lateral half of the ectotympanic ring is slightly caved in by approximately 1 mm along this crack. Other than such a distortion, the bulla seems to maintain its original proportions. The form of the bulla is quite inflated for a basal arctoid, more so than the modern ursid “type A” bulla (Hunt, 1974). The axis along the ventralmost rim of the bulla forms a slight angle with the parasagittal axis of the skull, in contrast to the canid condition of mostly parallel bullar axes. Composition of the bullar elements is difficult to ascertain due to extensive fusions and fine cracks on the bullar surface. An extremely subtle groove seems to run from the base of the paroccipital process across the posterior aspect of the bulla, crossing slightly behind the ventral floor of the bulla and reaching toward the anterior carotid foramen (the anterior extent of this groove is less well defined because surface marks are becoming less clear). This narrow band of slightly roughened area may be one possible interpretation of the rostral entotympanic– ectotympanic contact, although such an interpretation is highly speculative and other alternatives are just as likely. The posterior carotid foramen is located on the anterior rim of the large posterior lacerate foreman.

Toward the medial aspect of the bulla, the basioccipital–basisphenoid region is fractured, and anatomic relationships are difficult to interpret. The nearly vertical medial wall of the bulla is buttressed by a thickened lateral wall, up to 6 mm in depth, of the basioccipital. The lateral surface of this lateral wall of the basioccipital is essentially flat and hugs the medial wall of the bulla, although there is a narrow gap between these two walls toward the posterior aspect of their contact. The medial wall of the basioccipital lacks a prominent invagination for the embayment of the inferior petrosal sinus seen in many ursoids such as ursids, amphicyonids, and basal pinnipeds (e.g., Hunt, 1977; Hunt and Barnes, 1994). The above mentioned gap between the lateral wall of the basioccipital and the medial wall of the bulla-petrosal seems too small to accommodate an enlarged inferior petrosal sinus. On the medial side of the lateral basioccipital wall a small canal is embedded within the basioccipital bone. This canal, probably for a nutrient blood vessel, emerges anteriorly into the braincase slightly behind the level of the anterior carotid foramen.

The external auditory meatus is quite well developed for a basal arctoid. The ventral lip of the meatus is 3–4 mm long, much longer than those in European basal arctoids such as Amphicynodon leptorhynchus (FSP ITD 312) and Amphictis ambiguus (FSP PFRA 28). Areas inside the meatus were prepared. A suprameatal fossa is vaguely developed on the posterodorsal aspect of the meatal wall of the squamosal. Such a weak fossa is in contrast to that in the holotype, on which it is not only substantially deeper but also better defined by a sharp rim along its lateral and ventral aspects. The fossa in MAE SG.95.8919 is also less well developed than in Amphicynodon teilhardi (see description below). The postglenoid process is broken off, exposing the canal for the retroarticular vein, which is of relatively small caliber.

Mandible (fig. 7B–D): Discovery of the associated upper and lower jaws of MAE BU.91.9187–90 allows us confidently to refer several ramal fragments to Amphicticeps. Nonetheless, our knowledge of the angular process and the ascending ramus is still incomplete.

The mandible is short, thick, and deep, with an average thickness of 6.0 mm and depth of 11.0 mm (both measured at the level of the talonid basin of m1; N = 5). On AMNH 19127, the remaining ascending ramus suggests a rather erect anterior border, forming a 125° angle with the horizontal ramus. There are two mental foramina, one below the anterior edge of the p2 and another between the two roots of the p3.

Teeth (figs. 2, 7): No upper incisor is preserved. Only the root of right I3 is partially intact on AMNH 19010. A robust upper canine can be inferred from the large alveoli on both sides of the holotype. Immediately behind the canine is a small, single-rooted P1 with a single main cusp. The double-rooted P2 also has a single main cusp, which is surrounded by a weak cingulum on the lingual side. This cingulum thickens on the posterior end and shows an incipient development of a cingular cusp. Both P3s are missing on the type, but are well preserved in MAE BU.91.9187–90. Like P2, P3 is single cusped, although its cingulum is stronger than that on P2. The upper carnassial, P4, is transversely broad due to a lingually extended protocone, which is near the anterolingual corner of the tooth. The apex of the P4 protocone is relatively low and formed by a raised lingual cingulum. This crestlike protocone contrasts with that of the North American oligobunines, which have a primitively tall, cusplike protocone (i.e., the apex is not associated with the cingulum). A low crest is present on the labial aspect of the protocone. There is a narrow cingulum on the labial side, which continues in front of the tooth and thickens slightly to become an indistinct parastyle. A carnassial notch is present.

M1 is transversely elongated, and its labial border forms a steep angle, averaging 112°, with that of the P4. The M1 parastyle is strong, rising to nearly the same height as the paracone. In MAE BU.91.9187–90, there is a faint notch (absent in the holotype) separating the parastyle from the paracone. The paracone is much higher than the metacone. The preprotocrista is low and lacks a protoconule on the holotype but is swollen slightly at the base of the paracone to indicate an indistinct protoconule in MAE BU.91.9187– 90. The postprotocrista is clearly present and is oriented somewhat posteriorly. The postprotocrista ends at the posterior border of the M1 rather than at the base of the metacone. The lingual cingulum is moderately developed. It is rather low as compared to the protocone, and is thickest along the posterolingual border of the M1. The cingulum quickly tapers off anterior and posterior to the protocone, in contrast to a well-developed posterior ridge bordering a deep talon basin in the oligobunines. M2 is double-rooted and is located lingually such that its lingual border is at the same level as that of M1 whereas its labial border only reaches the middle of M1. The oval-shaped M2 has a prominent paracone toward the labial margin, and a posterolingually located, but much smaller, metacone at the posterior border of the tooth. A crestlike protocone is near the middle of the tooth, and is surrounded lingually by a lingual cingulum.

No lower incisors or canines are preserved on the holotype or referred specimens. The lower premolars are as robust as their upper counterparts. The p1 is single rooted and has a single main cusp. A cingulum is present around the anterior and posterior borders of p2–p3, which are single cusped. The p4, however, has a small posterior accessory cusp behind the main cusp. The p4 cingulum nearly completely surrounds the tooth except the region between the roots on the labial side. The m1 is rather broad (transversely) and its trigonid is short. The trigonid cusps are low and blunt, and the metaconid is not greatly reduced. The lingual border between the paraconid and metaconid is slightly concave to give a somewhat sigmoid appearance in occlusal view. Most individuals have a labial cingulum on the trigonid, whereas the lingual cingulum is more reduced. But the lingual cingulum is usually present at the level of the carnassial notch and may extend along the entire trigonid as in AMNH 21695, which occurs stratigraphically higher than the rest of the sample. The talonid of m1 is narrower than the trigonid, and consists of a dominant hypoconid bordered lingually by a low entoconid crest much like a cingulum. The anterior hypoconid crest, the cristid obliqua, is oriented parasagittally. There is a weak cingulum on the labial side of the hypoconid. The entoconid crest does not have a notch at the base of the trigonid as in Potamotherium and the oligobunines. The double-rooted m2 is shortened and nearly quadrate in outline. The protoconid and metaconid are large and distinct. There is no paraconid anterior to the protoconid and metaconid; in its place there is a low, triangular platform. The greatly reduced talonid consists of a small hypoconid along the posterolabial border of the tooth. The entoconid takes the form of a narrow cingulum. A narrow cingulum is also present along the labial border of m2. The presence of a tiny m3 is indicated by a small root in MAE BU.91.9187–90, but it is absent in other individuals (definitely in AMNH 19127 and probably in AMNH 19017).

Comparison:

Although Matthew and Granger's (1924) diagnosis of Amphicticeps shackelfordi indicated the presence of lower jaws, they did not elaborate the exact nature of the specimens, nor did they illustrate a lower jaw of this species. Four lower jaws were probably available at the time of their study (specimens that were collected during the 1922 season), and what Matthew and Granger had in mind were probably AMNH 19017 and 19128 because these two jaw fragments possess an m1 but are missing the m2, a combination that matches their descriptions. Their descriptions of the lower teeth, although very brief, must have been important in their attempt to delineate various species. In particular, their contrasts between lower carnassials of Amphicticeps and Amphicynodon (their Cynodon) must have been based on these referred lower jaws.

With the naturally associated upper and lower jaws of MAE BU.91.9187–90, our confidence in the references of isolated lower dental materials to Amphicticeps shackelfordi is considerably increased. In light of the new materials, Matthew and Granger's (1924: 4) comparisons about the lower carnassials having “a narrower and shorter heel with more distinct hypoconid crest” relative to those of Amphicynodon are still correct and their concept of the hypodigm still valid. However, specimens from the 1922 collection lack an m3, which naturally led Matthew and Granger to conclude that absence of this last molar is one of the main distinctions between Amphicticeps and Amphicynodon.

Our new discovery that MAE BU.91.9187– 90 has an unmistakable m3 adds a new wrinkle to the interpretation of this character. As pointed out in the above descriptions about specimens that have preserved the posterior dental battery, an m3 is definitely absent in AMNH 19127 and is probably absent as well in AMNH 19017. Given the tiny size of the m3 in MAE BU.91.9187–90, it is quite possible that individuals, such as AMNH 19217, could have had an m3 in an earlier part of their life, which was later broken and fully healed without leaving traces of its root, a situation common in carnivores with small p1s (personal obs.). Whatever the actual situation with AMNH 19217, taken at the face value of existing materials, 30%–50% of individuals have retained an m3, although our sample size is obviously too small to allow a true statistical sense of the ratios. A similar situation is better documented in the loss of the M3 in the basal canid Hesperocyon gregarius, in which about 7% of the Chadronian individuals still retain a small, nonfunctional M3 and by Orellan time all have lost it (Wang, 1994: 30). However, the actual ratio may not be an important point in the present analysis. The important phylogenetic implication is that Amphicticeps represents a small clade that in its most basal species, A. shackelfordi, is on its way to losing its last molars, and this loss is yet another independent disappearance of this molar among carnivorans.

It is also worth noting that AMNH 21695, the only referred specimen of A. shackelfordi from the Zavlia fauna well above the level of the persistent basalt, is also the most robust individual known, both in terms of ramal construction and width of the m1. In addition, it is the only individual with a nearly complete cingulum on the lingual side of the trigonid, and its premolar alveoli indicate an individual with a relatively shorter rostrum compared to individuals from the Ulaan Khongil fauna below or immediately above the lava. The reliability of these features as indications of a later stage of evolution of the species remains to be verified by further samples from the Zavlia fauna.

MAE SG.95.8919 offers the only bulla for Hsanda Gol carnivorans, and despite its less than certain taxonomic status, is of considerable importance in our understanding of the basal arctoids. That it belongs to the basal arctoids is certain. Of the main two arctoid lineages in the Shand Gol that are likely candidates, Amphicynodon teilhardi, the only species so far known for the genus in Mongolia, is too small for MAE SG.95.8919. Species of Amphicticeps, on the other hand, encompass a size range that is consistent with that of MAE SG.95.8919. More specifically, the holotype of A. shackelfordi has the same bulla size (judging from the attachment sites for the bulla) and general basicranial morphology as the MAE SG.95.8919. We thus cautiously place MAE SG.95.8919 in A. shackelfordi.

Overall, the holotype of Amphicticeps shackelfordi has a more robust construction than in MAE SG.95.8919, particularly in its thicker nuchal crests and larger and more laterally extruded mastoid process. These proportional differences may seem conspicuous, but probably are all attributable to a stronger development of the head–neck musculatures in the holotype. Even more extreme lateral expansions of the mastoid process can be seen in Allocyon. In the absence of contradicting evidence, we tentatively treat such differences as variations due to sexual dimorphisms in Amphicticeps. If our treatment is correct, the variations in the size of the suprameatal fossa are also considerable.

Holotype:

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

Type Locality:

Tsagan Nor Basin, eastern Valley of Lakes, Obor-Khangay 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 well-developed cingulum. The P4 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 well-developed 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 V-shaped 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 double-rooted 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.

Holotype:

MAE 93–213 (AMNH cast 129862), right maxillary fragment with P4– M1, partial P3, and alveolus of M2. Collected by James M. Clark on 16 August 1993.

Type Locality:

MAE 93–213 was found in the Tatal Gol (Ulaan Khongil or “Grand Canyon”) locality, 45°17′50″N, 101°37′16″E, Tsagan Nor Basin, eastern Valley of Lakes, Obor-Khangay Province, Mongolian People's Republic.

Geology and Age:

MAE 93–213 was collected from the main exposure of the Tatal Gol locality, below the level of the lava, in the Tatal Member of the Hsanda Gol Formation, early Oligocene.

Referred Specimens:

Holotype only.

Diagnosis:

As the largest and possibly the most derived species of the genus, Amphicticeps makhchinus is distinguished from the other two species of the genus, A. shackelfordi and A. dorog, in its larger size, a broadened P3 with an extra lingual root, a low and lingually expanded P4 protocone crest, a slightly more reduced M1 parastyle, an enlarged M1 metaconule, and a more expanded M1 lingual cingulum.

Etymology:

Mongolian: makhchinus, meat eater, carnivore.

Description:

Amphicticeps makhchinus is the least known of the three Hsanda Gol species of the genus. We are limited to two and a half teeth on the fragmentary right maxillary of the holotype. The maxillary clearly shows a shortened infraorbital canal, implying a shortened rostrum. Attached to this maxillary fragment is the anterior-most part of the jugal. The well-delineated jugal-maxillary suture indicates that the anterior jugal process stops at the antorbital rim and is probably not in contact with the lacrimal or frontal as in other species referred to this genus.

Only the posterior half of the P3 is preserved, which has a well-developed cingulum. The P3 has a significantly broadened lingual side and appears to have an extra lingual (third) root, in contrast to the double-rooted condition in other species of Amphicticeps. The P4 is typical of the genus, with a complete cingulum surrounding the entire tooth. The anterolabial corner of the cingulum is the strongest, but it does not elevate to form a parastyle. Like that of other species of Amphicticeps, the P4 protocone is composed of a raised lingual cingulum. However, the protocone is more expanded toward the lingual side than in the other species of the genus. As in the other two species of Amphicticeps, there is a low crest on the labial side of the protocone. The broad-based paracone has an anterior ridge leading up to the cingulum.

Overall proportions of the M1 have an anteroposteriorly broadened appearance for a basal ursoid. The parastyle is large and rises above the paracone, but does not reach to the same degree of expansion as seen in A. shackelfordi and is more similar to that of A. dorog. Likewise, the cingulum adjacent to the metacone shows no sign of reduction as in A. shackelfordi. Consequently, the angle between the labial borders of the P4 and M1 remains a relatively large 124°, 15° greater than in A. shackelfordi but almost identical to that in A. dorog. A distinct pre- and postprotocrista are present, the latter being slightly more posteriorly directed than in A. shackelfordi and A. dorog. There is no protoconule (paraconule) and the metaconule is only indicated by a vague platform (probably suffered from some wear) slightly raised above the surrounding areas. The M1 internal cingulum is broad and thick, much more expanded than in A. shackelfordi. An anterior spur of this cingulum is present near the base of the preprotocrista. M2 is missing. Its partial roots, however, indicate a transversely broadened M2 whose lingual border is more internal than that in the M1. Its labial border is flush with that of M1, similar to that in A. dorog but in contrast to a lingually shifted M2 in A. shackelfordi.

Comparison:

Amphicticeps makhchinus is the largest species of the genus so far known. It is 16% larger than A. dorog and 32% larger than A. shackelfordi (based on measurements of P4 labial length). It is 62% larger than Amphicynodon teilhardi. Besides its large size, A. makhchinus is also the most hypocarnivorous species in the genus. Dental features that indicate such hypocarnivory include an enlarged but low-crowned P4 protocone, a reduction of M1 parastyle, expansion of M1 lingual cingulum, a reduced angle between lingual borders of P4 and M1, and an enlarged M2.

Dental morphology of Amphicticeps makhchinus is reminiscent of certain ursids, particularly a basal ursid such as Cephalogale, so far known mostly in the Oligo-Miocene of Eurasia and North America. In particular, the French early Oligocene Quercy fissure fills produced some of the most primitive forms (e.g., Cephalogale minor). Similarities between A. makhchinus and Cephalogale include an enlarged grinding part of the dentition (M1–2) at the expense of the shearing part (P4). More specifically, A. makhchinus has a low, shelflike P4 protocone and a quadrate outline on M1, features often seen in Cephalogale. However, structural details of these features tend to argue against a true homology in the hypocarnivorous dentitions shared between A. makhchinus and Cephalogale. For example, the P4 protocone in all ursids (including Cephalogale) is formed by a swollen lingual cingulum, often in the form of a crest instead of a conical cusp, that has receded far back from the anterior border of the tooth, in contrast to an essentially conical protocone located on the anterolingual corner of P4 in A. makhchinus. Another derived character for the Ursidae is a posteriorly oriented postprotocrista of M1. This is a highly consistent feature among all known ursids. Such a condition is lacking in A. makhchinus (although wear in this region in the holotype of A. makhchinus renders our observation less certain). Finally, all ursoids, including the commonly acknowledged basal ursoids such as Amphicynodon, have a highly reduced parastyle and lingual cingulum on M1, in sharp contrast to a still relatively prominent parastyle in A. makhchinus.

Conversely, everything about Amphicticeps makhchinus is consistent with other species of Amphicticeps, despite its modest deviations toward the direction of hypocarnivory. Our inclination to assign it to Amphicticeps is further helped by the transitional nature of A. dorog between A. shackelfordi and A. makhchinus—in just about every aspect of its dental morphology A. dorog bridges the gap between the extremes in A. shackelfordi and A. makhchinus. In the final analysis, given what we know, it is easily conceivable that a series of three endemic species of Amphicticeps form a clade in the early Oligocene of central Asia.

Comment:

Cirot and Bonis (1992) recently revised the taxonomy of the genus Amphicynodon and furnished a cladistic relationship for included species. However, their diagnosis of the genus is almost entirely based on primitive characters (Cirot and Bonis, 1992: 105): “arctoide primitive; crâne alongé et bas, bulle ossifiée, fosse supraméatale superficielle, canal de l'alisphénoide present,” which essentially describe the morphotypical condition for a basal arctoid but shed no light of whether or not the genus forms a natural clade. As such the concept of Amphicynodon remains a grade of small, primitive arctoids that are not easily placed in other genera of carnivorans of similar ages.

Ten species of Amphicynodon were recognized by Cirot and Bonis (1992; see Baskin and Tedford, 1996, for a possible North American species). With the exception of A. teilhardi and A. mongoliensis (see below), all are from Europe and most are produced from the classic Quercy fissure fills. As defined by Cirot and Bonis, their concept of Amphicynodon offers a measure of morphological consistency, despite primitive status of most of their features. The limited scope of their phylogenetic analysis (within the genus), however, does not permit a sense of overall relationships among basal arctoids, nor does it address the question of to what extent the genus might be paraphyletic, given that certain derived forms (such as Pachycynodon and Cephalogale) may have arisen from within the genus. Such questions are difficult to address because most of the species of Amphicynodon are still represented by fragmentary jaws and teeth only. A comprehensive analysis of basal arctoids at the species level is not feasible. Our Mongolian materials, though significantly improved over those available for previous studies, are still not as complete as their European counterparts.

Holotype:

AMNH 19007, left ramal fragment with m1–2 and m3 alveolus.

Type Locality:

Loh, in Tsagan Nor Basin, eastern Valley of Lakes, Obor-Khangay Province, in north-central Mongolian People's Republic. In Tatal Member (“lower red beds”) of Hsanda Gol Formation, early Oligocene.

Referred Specimens:

AMNH 19014, right ramal fragment with p1–3, field no. 73; AMNH 19129, left ramal fragment with m1, from 10 mi west of Loh, “Grand Canyon”; AMNH 21628, left maxillary fragment with P2–4, field no. 532; AMNH 21673, left ramal fragments with p2, m1–3, and alveoli of c–p1, field no. 531, “Grand Canyon”; AMNH 84198, isolated left m1, field no. 531, “Grand Canyon”; AMNH 84212, left ramal fragment with m2–3 and m1 alveolus, field no. 532; MAE SG.8162, left ramus with p2–m1 (broken); MAE SG.9198–201, basicranium and maxillary fragments with left P2 and P4–M2 (AMNH cast 129861), and right M1–2, from loc. MAE M-174, 2 mi southwest of the Loh, on east side of a ridge, 45°16′14″N, 101°46′02″E, found not far above a brown sandstone layer, a local equivalent of the basalt lava (MAE M-174 is still within the Ulaan Khongil fauna that contains most specimens of Amphicticeps shackelfordi in Shand Member); MAE SG.9193, right maxillary fragment with P4–M2, from locality MAE 95-M-50, the Main Camp Locality, Tatal Gol, in Tatal Member; MAE SG.95.7488, left ramal fragment with broken p4 and m1; PST 17/34, anterior half of skull with complete right upper incisors, broken left and right canines, and complete left and right P2– M2, from Tatal Gol (Ulaan Khongil); PIN 475–3016, holotype of Cynodictis mongoliensis (Janovskaja, 1970: figs. 2–3), partial skull with complete left and right upper teeth and left ramus with p2–m3, from Tatal Gol (fig. 14); PIN 475–1388, partial palate with P3–M2 (Janovskaja, 1970: fig. 4); ZPAL MgM III/96, right ramal fragment with p3– m2 and m3 alveolus, Tatal Gol (Lange-Badré and Dashzeveg, 1989: 139); and ZPAL MgM III/97, left ramal fragment with p3–m1, Tatal Gol.

Distribution:

Early Oligocene of north-central Mongolian People's Republic. Dashzeveg (1996: fig. 1) reported that Amphicynodon teilhardi occurs in both the lower Tatal Member and upper Shand Member of the Hsanda Gol Formation. An undescribed record was reported in the early Oligocene Khatan-Khayrkhan locality of Altai Province of Mongolia by Russell and Zhai (1987: 324).

Emended Diagnosis:

As the only known species from Asia, Amphicynodon teilhardi differs from all European species of the genus, except A. velaunus, in its shortened m2, along with a correspondingly reduced M2, in contrast to a primitively long m2 and large M2 in most European species. A. teilhardi primitively retains a distinct posterior accessory cusp on p4, which is lost or extremely reduced in the European A. gracilis, A. speciosus, and A. velaunus. A. teilhardi further differs from European A. typicus, A. gracilis, and A. crassirostris in its relatively low hypoconid of m1 with wrinkled enamel, in contrast to a trenchant talonid in the latter three species.

Description:

PST 17/34 offers the best cranial morphology among all materials. Although it is missing the posterior one-third of the skull, the remaining skull of PST 17/ 34 is nearly perfectly preserved and offers fine details of bony and dental structures. Another cranial fragment, MAE SG.9198– 201, is less complete on the anterior part (consisting of a heavily crushed partial rostrum plus left orbital region) but preserved a partial left basicranium. In addition, we are in possession of a cast of a partial skull and mandible from the collection of the Russian Paleontological Institute, PIN 475–3016 (holotype of Cynodictis mongoliensis). In combination, much of the skull, except the posterodorsal portion, is known.

Skull (figs. 10, 11): The overall proportion of the skull is less specialized than that of Amphicticeps. The rostrum is not shortened and broadened and the temporal region is not elongated, as in the latter. The premaxillaries form a thin blade on either side of the nasal opening. The entire premaxillary is preserved. The posterior process of the premaxillary does not touch the anterior process of the frontal, and ends near the posterior tip of the canine root at the level of P1. Both nasals are broken anteriorly, and their posterior tips end at roughly the same level as the maxillary-frontal suture. The frontal process inserts between the nasal and maxillary and ends anteriorly at the level of the P2 main cusp. The frontal is slightly domed, in contrast to a flat forehead in Amphicticeps. The postorbital process is small and does not have the distinct protrusion seen in Amphicticeps. The orbit is relatively large and is of approximately the same size as that of Amphicticeps, which has a much larger skull. The distance between the postorbital process and postorbital constriction is 7 mm on PST 17/34 and 9 mm on MAE SG.9198–201, significantly shorter than the 12 mm of Amphicticeps, and thus has a far shorter temporal region than the latter. Furthermore, the postorbital constriction is not so narrow as in Amphicticeps. The temporal crests are very indistinct, and they converge more slowly toward the sagittal crest than in Amphicticeps. In PST 17/ 34, the temporal crests do not fully converge at the posterior edge of the broken skull, and the sagittal crest, if present, is not preserved.

In lateral view, the orbital region is best preserved on the right side of PST 17/34 (fig. 11). It is complemented by the partially preserved left orbital region of MAE SG.9198–201. The orbital mosaic is quite similar to that of Amphicticeps in several respects: a short infraorbital canal, presence of a shallow fossa in front of the antorbital rim (less developed in PST 17/34), a small, nearly rounded lacrimal bone with a lacrimal foramen near its anterior aspect, anterior process of jugal in contact with the lacrimal, and other topographic relationships among individual bony elements. Perhaps of phylogenetic significance is the shorter postorbital area between the postorbital process and postorbital constriction.

In ventral view, the incisive foramen (palatine fissure) is short and located at the level of the anterior aspect of the upper canine. A tiny foramen is present along the midline suture at the junction of the premaxillary and maxillary (foramen palatine medialis of Story, 1951), as is commonly seen in arctoids. The maxillary–palatine suture is mostly fused and difficult to recognize. The palatine foramen is somewhat behind the level of the P4 protocone. The posterior border of the palatine bone is anterior to the posterior border of the M2 and is distinctly indented by a semicircular notch on either side of the midline suture.

The width of the rostrum across P1s (measured on the lingual edge of the alveolus) measured 9.4 mm in PST 17/34. That for the laterally crushed rostrum on MAE SG.9198–201 measured 11 mm (restored from distorted left and right halves). These compare with 15.2 mm for the same measurement in Amphicticeps shackelfordi—the rostrum of Amphicynodon teilhardi is on average 49% narrower than the former. Given a size difference of 22% for the average length of P4 between these two species, the width of the rostrum in A. teilhardi is also relatively narrower than that of the type species. See additional cranial measurements (table 2) for PST 17/34.

Basicranium (fig. 12): The fragmentary materials of MAE SG.9198–201 offer the only information about the basicranium of Amphicynodon teilhardi. Although heavily crushed dorsoventrally, the left side of the basicranium of MAE SG.9198–201 preserves several key anatomical features absent in Amphicticeps. The overall basicranial morphology of Amphicynodon teilhardi is somewhat similar to that of Amphicticeps. The most obvious similarities are the presence of a shallow suprameatal fossa and a laterally expanded squamosal blade for the dorsal roof of the external auditory meatus. Much of the posterior half of the mastoid process is lost. However, the process is less laterally protruded than in Amphicticeps, judged from a more vertically oriented lateral wall of the braincase that forms a 90° angle with the horizontal squamosal shelf, in contrast to Amphicticeps, in which far more inclined lateral braincase walls (in posterior view) almost continue into the mastoid process. The suprameatal fossa is slightly less well developed than in Amphicticeps. In particular, its lateral half is not so deeply excavated into the squamosal as in Amphicticeps, and it does not have so clear-cut a lateral rim as in the latter.

The basisphenoid area is fragmented, and the ventral floor of the alisphenoid canal is broken off. However, enough is preserved in the area surrounding the foramen rotundum to indicate the presence of a canal, that is, the presence of a deep groove on the alisphenoid that probably forms its posterior opening. A small foramen opens into the medial wall of the canal at the level of its posterior opening.

The postglenoid process is large, forming a long ventral hook for articulation with the condyle of the mandible. At the posterior base of the postglenoid process, behind the postglenoid foramen, there is a triangular piece of ectotympanic still firmly attached to the basicranium. Part of the anterior ectotympanic ring for attachment of the tympanic membrane is also preserved. The ectotympanic does not extend laterally far beyond the postglenoid foramen, indicating no or a very short bony external auditory meatus. On the medial side, along the suture between promontorium and basioccipital, several broken pieces of the entotympanic are still preserved and cover the internal carotid canal. The ventral flooring of the canal, presumably formed by the caudal entotympanic, forms a gentle curve in a typical primitive arctoid fashion, leading toward the middle lacerate foramen. The presence of this medially positioned carotid canal further confirms our conclusion that there is no promontorial artery in Amphicynodon and Amphicticeps, despite of the sulci on ventral surface of the promontorium in the holotype of Amphicticeps shackelfordi (see description under that species). No sulcus is visible on the promontorium of A. teilhardi.

The promontorial part of the petrosal has been pushed dorsally toward the brain cavity, and its ventral surface is unnaturally rotated into a vertical orientation. The ventral promontorial surface has thus become laterally facing and is partially hidden beneath the lateral edge of the basioccipital. The postmortem crushing of the promontorium into the brain cavity, however, is apparently beneficial for the preservation of a nearly complete malleus and incus, which occupy the space originally occupied by the promontorium.

The malleus lies on its medial side with the lateral surface (for attachment of the tympanic membrane) of the manubrium facing ventrally. The malleus has a rather slender construction but is of large size—the head to manubrium tip (broken) measures 5.8 mm. The lateral process is inconspicuous. The muscular process (for insertion of m. tensor tympani) is broken near its base and its main body sticks out between the anterior process and the manubrium instead of its original position, pointing away from the plane of tympanic membrane. This slightly dislocated muscular process is very large and has a broad distal end, which contrasts with the much reduced condition in living ursids (Segall, 1943). The neck is slender and forms a smooth curve between the head and the manubrium. The head is not enlarged as in pinnipeds (Wyss, 1987). The sharp-tipped anterior process completes the anterior rim of a circular lamina. Much of the incus is buried beneath the head of the malleus. Only the processus brevis is fully exposed.

Upper teeth (figs. 13A–C, 14): Most of the upper dentition is now known. Upper incisors in PST 17/34 are all broken and the crown morphology is no longer preserved. The roots indicate progressively enlarged incisors from I1 to I3, with the I3 almost twice as large as the I1. All incisor roots are mediolaterally compressed. The left and right I3s in PIN 475–3016 are preserved and are slightly precumbent in lateral view, as is also the case in PST 17/34. The upper canines on both sides are also broken in PST 17/34, preserving only the roots. The canine roots are oval in cross section. The canines in PIN 475–3016 are present. The canine crowns are smooth surfaced and their tips curve backward slightly.

The cheek teeth are evenly spaced with short alveoli between all premolars in PST 17/34 but slightly more tightly spaced in PIN 475–3016, in contrast with crowded premolars of Amphicticeps due to its shortened rostrum. P1 is only seen in PIN 475–3016, and is single rooted. It has a simple main cusp and an indistinct cingulum anteriorly and posteriorly. The P2s are single cusped and are more slender than that of Amphicticeps. A rather tall and erect main cusp has a posterior ridge and an anterolingual ridge. The anterior and posterior cingula are slightly more distinct than in the P1s, but there is no cingular cusp on either end. The cingulum is continuous on the lingual side and discontinuous on the labial side. The main distinction between P3 and P2, besides a larger size and more prominent cingulum in the P3, is a slight swelling on the posterolingual cingulum of the tooth, but there is no extra root beneath this swelling. The morphology of P4 is similar in overall construction to that of Amphicticeps, except for a much smaller protocone. A distinct cingulum surrounds the entire tooth. The anterior cingulum is particularly well developed, as is the parastyle. However, the parastyle is not cusplike but more like a wide cingulum. As in Amphicticeps, the anterior border of the P4 protocone is slightly ahead of the parastyle. The protocone apex is clearly continuous with the lingual cingulum. The cuspidate protocone has an indistinct ridge on the labial side of the cusp. The paracone has a distinct anterior ridge reaching up to the parastyle, and a less distinct anterolingual ridge that reaches to the base of the protocone. A deep carnassial notch separates the paracone from the metastylar blade.

The overall construction of M1 is less hypercarnivorous than that of Amphicticeps. The M1 parastyle is substantially reduced as compared to those of Amphicticeps, even for the least developed M1 parastyle in A. makhchinus. A vague notch separates the parastyle and paracone. The labial cingulum is slightly swollen around the paracone in PIN 475– 3016 and around the right M1 of PST 17/34, similar to the swellings in Amphicticeps shackelfordi. The labial cingulum near the metacone is not so reduced as in Amphicticeps; this is especially so in MAE SG.9193. Together, the smaller parastyle and less reduced labial cingulum along the metacone give M1 a more quadrate look. The labial borders of P4 and M1 form an angle of 127°, 18° larger than in Amphicticeps shackelfordi. The differences in size and height between paracone and metacone are also relatively smaller than in Amphicticeps. There is a well-developed preprotocrista and postprotocrista. There is no protoconule, except a slight swelling in PST 17/34, which is absent in the Russian specimens. The postprotocrista is essentially posteriorly oriented, particularly so in PST 17/34, leaving a broad valley between the postprotocrista and metacone. A metaconule is only vaguely suggested by a low and indistinct swelling at the posterior end of the postprotocrista and by a slight notch toward the posterior end of the postprotocrista. The internal cingulum (hypocone) surrounds the entire protocone, although its anterior segment is narrower. This anterior extension in front of the protocone, less well developed in MAE SG.9193, has a narrow spur near the base of the preprotocrista.

M2 has the same distinct shape as in Amphicticeps, reaching the same stage of reduction and acquiring the same peculiar cusp pattern as in the latter, although this tooth tends to vary more than does M1. A large paracone is located at the labial border of the tooth, whereas the metacone is reduced to a faint cusp at the posterior border (that in PST 17/34 is more distinct). The protocone is relatively large and is in the middle of the tooth, followed lingually by a broad cingular shelf. The main feature to be distinct from that of Amphicticeps is its less lingually shifted position. Instead of being flush with the lingual border of the M1 as in Amphicticeps shackelfordi, the lingual border of M2 in Amphicynodon is slightly lateral to the M1 lingual border.

Lower teeth (figs. 13D–F, 14): Lower jaws figured by Janovskaja (1970: figs. 3, 5, 6) substantially improved the knowledge of Amphicynodon teilhardi over the original topotype series. The following descriptions of the ramus are based on figures published by Janovskaja. Her dental illustrations, however, lack sufficient details for useful comparisons, and have exaggerated the length of the m2 (see table 7 and comparison below), a critically important feature of this species. Our dental descriptions are mainly based on a cast of the PIN 475–3016, as well as more fragmentary materials from the AMNH.

The horizontal ramus is relatively slender compared to that of Amphicticeps. The ascending ramus has a rather erect anterior border. The angular process is slender and pointed. No lower incisor is preserved. The lower canine hooks backward slightly. The lower premolars are relatively more slender than those of Amphicticeps. The p1 is not preserved. The p2 has a simple main cusp and a very vague cingulum. The p3 begins to have a tiny posterior accessory cusp and a slightly more distinct cingulum. The p4 posterior accessory cusp is further enlarged, and its cingulum surrounds the entire tooth. The anterior cingulum has a hint of developing into an anterior cingular cusp, and the posterior cingulum is also slightly elevated.

The m1 trigonid is tall crowned. The metaconid is approximately the same height as the paraconid. The metaconid is on the lingual side of the protoconid, not trailing behind the protoconid as seen in most ursids. A cingulum is present on the entire labial margin of m1 but is only vaguely present on the lingual side of the paraconid. The m1 talonid is low, especially the hypoconid. The hypoconid is largely crestlike and is oriented at a slight angle from the anteroposterior axis of the tooth. Anteriorly, the hypoconid crest ends at the base of the protoconid just below its apex. The entoconid consists of a low ridge, rather like a cingulum. Together with the hypoconid, the entoconid encloses a broad basin on the talonid. The talonid cusps are decorated with fine wrinkles. The m2 is small and distinctly short; its length and width are nearly identical. No paraconid is visible. A protoconid and metaconid are of equal height and positioned on the borders of the tooth, such that a central valley essentially runs through the length of the tooth. A small cristid connects between the protoconid and metaconid in the holotype but is absent in PIN 475–3016. On the talonid, the hypoconid is far better developed than the entoconid, which is absent in the holotype. A small m3 is present in all specimens that preserve this part of the jaw. It is formed by a small, rounded, peglike structure with a surrounding cingulum but without a distinct cusp pattern.

Comparisons:

The topotype series of Amphicynodon teilhardi consists of a few jaw fragments and lower teeth without upper teeth. Based on such meager materials, Matthew and Granger (1924: 8) were initially ambivalent in their assignment of this species to Cynodon (Amphicynodon of current usage): “This species can be referred only provisionally until better specimens are available. It appears to fall within Pachycynodon rather than the typical Cynodon, by Teilhard's key to the Phosphorite genera,” in reference to Teilhard de Chardin's (1915) monographic revision on Quercy carnivorans that dealt with these genera. The first major breakthrough in the state of knowledge of this species came by a crushed but associated skull and lower jaw (PIN 475–3016; fig. 14) along with a few more specimens collected by the 1946–1949 Expeditions of the Soviet Academy of Sciences. The Russian collection was described as a new species, Cynodictis mongoliensis, by Janovskaja (1970). While describing three additional jaw fragments collected by the Polish–Mongolian Paleontological Expeditions in the 1960s, Lange-Badré and Dashzeveg (1989: 141), however, argued that “there are no significant morphological or biometrical differences between C. mongoliensis and A. teilhardi and those that exist represent no more than intraspecific variation.” More recently, Cirot and Bonis (1992), in their phylogenetic analysis of the species of Amphicynodon, chose to leave Amphicynodon mongoliensis as a valid species, and in their cladogram, placed it next to A. teilhardi as the sister-species forming an Asiatic clade.

Although we are unable to examine the three jaw fragments in the ZPAL collection (Lange-Badré and Dashzeveg's measurements for the holotype of A. teilhardi are apparently an underestimate), we have access to casts of two PIN specimens in the topotype series of C. mongoliensis. With the addition of even better materials from the MAE collections, we are in a position to evaluate morphological variations of at least 20 specimens (see table 7). Although the increased sample size naturally leads to a slight increase in variations, the coefficient of variation for most dental measurements generally falls between 5% and 8%, a range not uncommon for small carnivorans (e.g., Wang et al., 1999). The only exceptions are for the upper canines, which tend to be more dimorphic among arctoids, and the m2s, which have the least occlusal constraint because of their flat grinding surfaces. Cirot and Bonis (1992: 119 and fig. 16) noted the rather long m2 in A. mongoliensis, apparently on the basis of Janovskaja's (1970: fig. 3) illustration of the holotype, and assigned this presumed long m2 as an autapomorphy for the species. Our own examination of a plaster cast of PIN 475–3016 shows no elongation of the m2 (fig. 14). In fact, our own measurements on the cast indicate a shorter length than the width for the m2 (3.0 mm in length and 3.2 mm in width), in sharp contrast to an elongated m2 shown in Janovskaja's figure. It seems clear that the m2 length in Janovskaja's illustration was exaggerated (the lack of morphological details in her illustration of the m2 further undermines the reliability of her published line arts). In our examinations of the rest of the dentitions, we failed to detect any substantial difference, either in size or shape, between the Russian collection and the rest of the samples. We thus fully agree with Lange-Badré and Dashzeveg that Cynodictis mongoliensis is synonymous with Amphicynodon teilhardi. The combined materials from AMNH, PIN, ZPAL, and MAE allow more confident assignments of fragmentary specimens and, as a result, increased morphological cohesion of this species.

Lange-Badré and Dashzeveg (1989: 141) chose to compare the Mongolian form with three Quercy species of Amphicynodon: A. typicus, A. leptorhynchus, and A. gracilis. They concluded that A. teilhardi was closer to A. leptorhynchus or A. typicus than to A. gracilis. Characters that were cited to indicate such a relationship include the wrinkled enamel and a reduced m2 paraconid. A revision of the systematics and phylogeny of Amphicynodon by Cirot and Bonis (1992: 119 and fig. 16), on the other hand, recognized 10 valid species, 8 European and 2 Asian, and suggested a relationship almost opposite to that suggested by Lange-Badré and Dashzeveg. Cirot and Bonis placed A. teilhardi (along with A. mongoliensis; see comments above) as the sister-taxon to the terminal clade formed by A. gracilis and A. cephalogalinus, whereas A. leptorhynchus and A. typicus are further down the tree in more basal positions. A critical synapomorphy cited in support of above relationship was a “trigonide de M/1 disjoint” shared by A. teilhardi, A. gracilis, and A. cephalogalinus (Cirot and Bonis, 1992: fig. 16, node 10). In their remarks on A. teilhardi (Cirot and Bonis, 1992: 119), this character was explained as an open trigonid due to a reduction and a posterior position of the metaconid of m1 (“un trigonide ouvert en raison de la réduction et de la position reculée du métaconide”). Lange-Badré and Dashzeveg's character, a reduced m2 paraconid, was pushed further down the tree by Cirot and Bonis and was shared by A. velaunus, A. leptorhynchus, A. teilhardi, A. gracilis, and A. cephalogalinus. While it is beyond our scope to reevaluate species relationships of Amphicynodon, we note that Cirot and Bonis's character of a disjoint m1 trigonid is not readily apparent in their illustrations of three of the four species of Amphicynodon that are supposed to share it. On the other hand, their illustration of A. leptorhynchus (Cirot and Bonis, 1992: fig. 3), a species that was supposed to possess a primitive condition for this character, shows a more posteriorly displaced m1 metaconid than in any other species. Our own examination of some of Cirot and Bonis' materials in the Université de Poitiers, which form the partial basis of their systematic revision, fails to substantiate the validity of this character. Such a character, if it does exist, must be quite subtle at this stage of its evolution. In our observations, the presence and absence of an m2 paraconid does seem to be a valid character that unites some species of Amphicynodon, including A. teilhardi.

As for the generic status of the Mongolian species, Lange-Badré and Dashzeveg (1989: 141) rejected the initial suspicion by Matthew and Granger (1924) that the Hsanda Gol form was closer to the European Pachycynodon than to Amphicynodon: “C. teilhardi belongs unquestionably to the genus Amphicynodon. It differs from Pachycynodon in the situation of the metaconid on m1, in the open basin, in the wrinkled enamel, in the reduced paraconid and entoconid in m2 and in the ratios of the talonid and trigonid on m2.” Cirot and Bonis (1992) more explicitly placed A. teilhardi among the rest of the European species of the genus. In light of the entire dentition available in this study, A. teilhardi falls within the overall parameters of the genus. However, since Amphicynodon, as a basal ursoid, was long suspected to have given rise to other clades (e.g., Teilhard de Chardin, 1915), it is likely a paraphyletic genus in a strict cladistic sense—various species may ultimately be shown to be more closely related to other clades. Until a comprehensive, species-level phylogenetic analysis is done, current concepts of Amphicynodon remain largely gradational. See table 1 for more contrasts of morphological differences between Amphicticeps and Amphicynodon.

Referred Specimen:

MAE SG.97.5396, left ramal fragment with m2.

Comments:

MAE SG.97.5396 (fig. 15A– C) is clearly not assignable to the Hsanda Gol ursoids discussed above. The size of the m2 indicates an animal of the size of Amphicticeps dorog, but it does not have the extremely shortened m2 of the latter. Indicating its primitive status, MAE SG.97.5396 has a paraconid platform in front of the protoconid, and the paraconid is separate from the protoconid by a weak notch. A paraconid is absent in the Hsanda Gol Amphicticeps and Amphicynodon. Furthermore, the protoconid and metaconid are not widely separate from each other, as in both of the above genera. The morphological condition in MAE SG.97.5396 evokes that of a more primitive carnivoran, and the fact that it has an m3 alveolus tends to suggest a basal arctoid among known lineages in this period of time.

In size and overall proportions, MAE SG.97.5396 is closest to a recently described small arctoid, Pachycynodon tedfordi Wang and Qiu, 2003, from the early Oligocene Saint Jacques locality of Chinese Inner Mongolia (see further comments below about its generic status). Unfortunately, the m2 on the Chinese specimen is too worn to permit detailed comparisons.

Comments:

Pyctis inamatus was named on the basis of a left jaw fragment with p3 (broken)–m1 and partial m2 alveolus from the Tatal Gol area in a “red claystone unit, SW of Maikant, 16.9 m above the lava layer in the Shand Member” (Babbitt, 1999: 791). With an m1 length of approximately 11 mm, Pyctis is somewhat smaller than Amphicticeps makhchinus (arctoids tend to have a somewhat shorter P4 than m1; the reverse is true between Pyctis and A. makhchinus) but falls in the range of A. dorog (see measurements in tables 3, 5). Pyctis is highly hypercarnivorous with an extremely trenchant m1 talonid, which has a single, centrally located hypoconid, along with the complete loss of m1 metaconid. This dental pattern is almost exactly opposite to that in A. makhchinus, which tends toward the hypocarnivorous direction. Pyctis is also more hypercarnivorous than A. dorog, which still retains a substantial m1 metaconid and entoconid. Another important difference between A. dorog and Pyctis is the presence of a posterior accessory cusp on the p4 of the former, which is lacking in the latter.

Babbitt (1999) compared Pyctis with some basal mustelids from the early Miocene of Europe, such as Plesiogale and Paragale, and she also made comparisons with later Eurasian forms, such as Eomellivora and Mellivora. Given the poor condition of the holotype, she did not draw definitive systematic conclusions, except placing it in the family Mustelidae.

Pyctis also shares some resemblance to certain oligobunines (a group of basal musteloids) in the late Oligocene through early Miocene of North America (Baskin, 1998a), such as Oligobunis and Megalictis, which also have a highly hypercarnivorous lower carnassial and reduced posterior accessory cusp on p4. On the other hand, Ischyrictis and Hoplictis from early to middle Miocene of Europe also exhibit tendencies toward hypercarnivory (Ginsburg and Morales, 1992). The systematic status of Pyctis will remain uncertain without additional materials, particularly its upper teeth.

Relationships within Amphicticeps:

Given the limitation of the fragmentary materials in two of the three recognized species of Amphicticeps, a comprehensive phylogenetic analysis using the full spectrum of cranial and basicranial characters listed above is not feasible. Instead, we tacitly assume that cranial and basicranial characters for A. dorog and A. makhchinus are similar to those of A. shackelfordi and that they mainly differ by dental morphology and size. Based on dental characters, relationships among species of Amphicticeps appear to fall in a linear progression, starting from the small A. shackelfordi, transitioning through the intermediate A. dorog, and ending in the large A. makhchinus.

Using Miacis and Hesperocyon as outgroups, character transformations within Amphicticeps can be deduced to show the following trends. A basal status for A. shackelfordi is indicated by such primitive characters as relatively less robust dentitions, small but high-crowned P4 protocone, large M1 parastyle, and the presence of an m3 in some individuals. A. shackelfordi may have one autapomorphy of its own: a reduced and lingually shifted M2, a condition that parallels that in the basal musteloid Potamotherium.

Amphicticeps dorog is obviously more derived than A. shackelfordi in the following characters: larger size and more robust dentitions and jaws, a more crestlike P4 protocone that is relatively lower crowned, a slightly more distinct P4 anterior cingulum, a reduced M1 parastyle (and consequently a larger angle between the labial borders of the P4 and M1), and the loss of an m3. A. dorog also has a larger and more labially positioned M2.

Amphicticeps makhchinus is apparently the most derived species of the genus. Compared to A. shackelfordi and A. dorog, A. makhchinus is the largest in size, has the broadest P3, possesses the lowest and most enlarged P4 protocone crest, and features the most reduced M1 parastyle, the largest M1 metaconule, and the greatest expansion of M1 lingual cingulum. A. makhchinus also hints at a relatively large and labially positioned M2. Most of the above derived characters in A. makhchinus suggest a modest tendency toward hypocarnivory, paralleling some dental characters of the ursids.