PDYV 2000 is a complete but bilaterally compressed snout and dentition that has also suffered some plastic deformation (Fig. 3 and Fig. 4). It lacks most of the neurocranium. The right anterior part of the zygomatic arch is preserved.

Lateral view: the snout is long, the anterior tip of the nasal bone is broken, but it terminates slightly behind the anterior extremity of the premaxilla (Fig. 4-1). The flange above the canine is not very developed, nor is it elongated antero-posteriorly. The anterior root of the zygomatic arch extends laterally, and it departs from the maxilla at a right angle opposite M1/, while the rear part of the zygomatic root is below the anterior of the orbit. The anterior edge of the arch is relatively slender, but the lateral and posterior parts are robust with extensive fossae for the origin of the levator rostri musculature (Fig. 4-1). The anterior edge of the orbit lies above the pterygoid process of the palatine, the orbit is rounded and of medium size. The supraorbital process is distinct, the supraorbital crest is well developed, and the infraorbital foramen is above P3/ and P4/. The distance from the anterior edge of the orbit to the front of the premaxilla is 260 mm.

Ventral view: the palatine (Fig. 3-2) is long and on the left side it is possible to see that palatine foramen is opposite to the postero-lingual side of M2/. The incisive foramen is opposite to the postero-lingual end of I1/ and the antero-lingual part of I2/, and is elliptical in outline. All three incisor alveoli are preserved, those for I1/ and I2/ are large and deep, but the alveolus of I3/ is small and located on the lateral surface of the snout immediately above a low occlusal ridge on the premaxilla, and behind the alveolus of I2/. According to the preserved section of the canine in the alveolus, it was not very large. The P1/ is preserved on the right side, the P2/–M1/ are heavily worn, but the M2/ and M3/ are lightly worn, suggesting that the individual was fully adult when it died but was not senile. There is no diastema between P1/ and P2/, but between P1/ and the upper canine there is a gap of 10 mm, and between the canine and I3/ the diastema is 22 mm long. P1/–M3/ is 132 mm, the premolar row (P1/–P4/) is 62 mm, M1/–M3/ is 70 mm, and the distance from the pterygoid process of the palatine to the anterior tip of the premaxilla is 266 mm. The pterygoid process of the palatine and sphenoid is situated 25 mm behind the M3/.

Occipital view: the neurocranium is missing and only the left frontal sinus can be observed.

Dorsal view: the facial part is much narrower than it would have been in life due to the compression and distortion that the specimen has undergone (Fig. 3-1). The nasals and anterior part of the frontals are compressed and have been deformed into a wide crest. The frontals and anterior part of the parietals have been crushed, the posterior portion of the parietals is missing. The supraorbital foramen is located above the orbit, and is oval in outline. Behind the postorbital process the two parietal crests run posteriorly and quite sharply sagittally and approach each other closely, but because the neurocranium is broken at this point it is not possible to determine whether they joined to form a sagittal crest.

PDYV 0070 and PDYV 0071 are two maxillae with P1/–M1/, belonging to the same individual. Although they are separated at the midline of the palate, palatal width at P2/ can be estimated to be ≥ 44 mm. In the left maxilla (PDYV 0070), the diastema between P1/ and C1/ is 12 mm, whereas on the right one (PDYV 0071) it is 10 mm. The length of the left premolar row (P1/–P4/) is 59.5 mm, while on the right side it is 55.5 mm. The left maxilla is slightly distorted.

The central upper incisor (Fig. 5-1a and b) is typical of the Propotamochoerini, with several ridges and grooves on the occlusal and distal aspects, and a smoother labial surface.

The first upper premolar (Fig. 5-2) consists of a central main cusp with rounded anterior and posterior margins, and there are lingually curved anterior and posterior crests ending in accessory cusplets, and there is a disto-lingual cingulum. It has two roots.

The second upper premolar (Fig. 5-3) is a larger and wider version of P1/, and there is a bigger disto-lingual cusplet, the base of the cusp is inflated on its lingual side, from which a beaded lingual cingulum runs anteriorly and posteriorly. It has two roots.

The P3/ (Figs. 5-4 and 5-6) is approximately triangular in occlusal outline, the lingual cusp is located forwards of its usual position in suids, being almost at the same level as the main cusp, and for this reason the widest part of the tooth is in the middle. The lingual cusp is almost as high as the main cusp. The main cusp of P3/ is oriented diagonally, forming an angle of about 30° to the sagittal plane of the skull. Behind the main cusp there is a closely applied secondary cusp, which blends into the main cusp after slight wear. The lingual cingulum is developed forwards to connect with the anterior cusplet and backwards to connect with the posterior cusplet. In the sagittal valley there is small beaded cusplet. The tooth has three roots, one anterior and two posterior.

The P4/ (Figs. 5-5 and 5-6) is trapezoidal in occlusal outline, and is almost completely molarised, being comprised of four main cusps arranged in two transverse pairs. Most specimens are slightly longer mesio-distally than bucco-lingually. The two buccal cusps are wide apart, and lingually there is a distinct cusp (hypocone) behind the protocone. The protocone is displaced forwards in line with the paracone, and the hypocone is the smallest cusp. There is a small cusplet in the sagittal valley. The anterior accessory cusp is distinct, but there is no distal one. The lingual cingulum is well developed and the lingual flare is marked. There are three roots, two buccal ones and one lingual.

The M1/ (Fig. 5-7) is approximately rectangular in occlusal outline, and it has four similar sized main cusps, with anterior, median and posterior accessory cusplets, and anterior and posterior cingula. The main cusps are not high, the enamel is moderately thick and is wrinkled, the furchen are shallow, and the median transverse valley is not wide.

The M2/ (Fig. 5–8, Fig. 5–10) is a larger version of M1/, but is proportionally longer.

The M3/ (Fig. 5-11) is approximately trapezoidal in occlusal outline, and is composed of four main cusps and a talon, The anterior two lophs are morphologically similar to M2/, the talon is about 1/4 of the total length of the tooth, and consists of three flat cusps, the lingual one being the largest, the buccal cusp being small. The rear half of the tooth narrows perceptibly distally.

The dM4/ (Fig. 5-9) is similar to M1/ save for its more trapezoidal outline, and the less well pronounced main cusps.

PDYV 1666 is part of a horizontal ramus of a mandible carrying p/3–m/3, but the ascending ramus is missing. The mandibular body is slender, and the cheek teeth are in medium wear.

PDYV 0878 is a slender horizontal ramus preserving its ventral margin, containing m/1–m/3.

PDYV 0766 is a well-preserved left horizontal ramus where m/2–m/3, c/1 to m/1 have been lost, but the roots are preserved, part of m/2 is damaged, but the m/3 is intact (Fig. 5-17). The body is robust, and the base of the mandible broadens anteriorly. The root of the canine preserved in the alveolus is large, from which we infer that the jaw probably represents a male individual. There is a pair of mental foramina below the p/1, which are close together, and there is a field of small pits above them, presumably for firm attachment of the skin or other superficial tissue. There is also a foramen below p/2–p/3.

In PDYV 0766 the basal mandibular width at p/2 is 38 mm, the diastema between p/1 and p/2 is 9 mm, the length of the premolar row (p/1–p/4) is 131 mm, and p/2–m/3 is 114 mm. Other measurements of the mandible are provided in Table 2.

Canines are of the ‘verrucose’ type, some specimens are larger than the others, perhaps reflecting sex differences.

The p/3 (Fig. 5-12) has an elongate crown, and there is a shallow groove behind the main cusp, which would disappear with light wear. The anterior accessory cusp is half the height of the crown, the talonid is high, and there is a groove separating it from the main cusp. The talonid is somewhat inflated on its lingual side. In fact, this tooth looks like a p/4 of Propotamochoerus.

The p/4 (Fig. 5-14) of Molarochoerus is approximately rectangular in occlusal outline, the anterior part being slightly wider than the posterior half. This tooth is completely molarised, possessing four main cusps arranged in two transverse pairs. The two main anterior cusps (protoconid and metaconid) are separated by a deep and wide groove, the lingual cusp is almost the same height as the buccal one, and is slightly posterior to it. The antero-buccal cusp is obliquely oriented and its anterior crest runs obliquely anteriorly towards the lingual side, terminating at the base of the anterior part of the lingual cusp where it forms a small, low anterior accessory cusp. The posterior crest of the antero-buccal cusp runs slightly obliquely towards the buccal end of the floor of the median transverse valley. In some specimens this posterior crest is not well developed, and in these few teeth the antero-buccal cusp is lower. There is a well-developed median accessory cusp behind the two main cusps, which is lower than the main cusp and has a crest linking it to the buccal main cusp, which itself is slightly obliquely oriented. The talonid is nearly the same height as the main cups, and its morphology recalls the posterior part of m/1, the entoconid and hypoconid being located at the same level opposite one another but separated from each other by a deep groove. The hypoconulid is situated to the postero-lingual side of the hypoconid. There is an anterior cingulum, but none posteriorly. The tooth has three roots, one anteriorly (incipiently bifid) and two posteriorly.

The m/1 (Figs. 5-13 and 5-15) is rectangular in occlusal outline with four main cusps. The crown is low, the lingual cusps being slightly higher than the buccal ones. The median accessory cusp and groove system are well developed. There are one or two basal pillars in the buccal end of the median transverse valley, the lingual side not having any. The anterior and posterior cingula are well developed. The hypoconulid is strong but the anterior accessory cusp is indistinct.

The second lower molar (Figs. 5-16 and 5-17) is an enlarged version of m/1.

The m/3 (Fig. 5-17) consists of four main cusps and a talonid. The two anterior lophs are similar to the m/2, behind which there are three small cusps forming the talonid. Of these the buccal one is the largest. The talonid is narrower than the two anterior lophs and is positioned towards the buccal side of the crown, and it comprises 1/4 of the length of the tooth.

The dm/4 (Fig. 5-13) is composed of three lophs, the anterior part is narrower than the posterior part, and there is a distinct accessory cusplet in the centreline of the tooth behind each loph.

In lateral view the origin of the levator rostri musculature in Molarochoerus occupies a vast area extending from behind the infraorbital foramen anteriorly to the orbital margin posteriorly and from the nasomaxillary suture dorsally to the ventral edge of the zygomatic arch ventrally (Fig. 4(1)). This area is huge when compared with the conformation in Sus scrofa (Fig. 4(2)). It is much larger than in Propotamochoerus hysudricus [13] and Microstonyx major [7], but its position and the lateral flare of the zygomatic arches of these genera are comparable, suggesting that Molarochoerus is closely related to them, and was probably derived from one or other of them, most probably the former. In Molarochoerus, the origins of the depressor rostri and dilatator naris lateralis muscles are located beneath the zygomatic arch in an area where the arch thickens medio-laterally, as in Propotamochoerus and Microstonyx. The homologous muscle origins in Sus scrofa occur on the lateral surface of the maxilla, separated from that of the levator rostri by a prominent but low crest. In addition, in Sus the ventral margin of the zygomatic arch is slim, and not at all medio-laterally expanded (Fig. 4–2), [18] unlike Microstonyx in which it is inflated and occupied by extensive sinuses [7]. The impression obtained from the vastness of the origin of the levator rostri muscle in Molarochoerus, allied to the depth of the fossa and the robustness of the surrounding bone margin is one of immense muscular power. The same impression is obtained when examining the ventral margin of the zygomatic arch, indicating powerful depressor rostri and dilatator naris lateralis muscles.

The function of all these muscles relates to the rostral disc, which in pigs occurs at the anterior extremity of the snout [3] and [4]. The disc is rotated dorsally, ventrally and laterally depending on which muscle is acting. When more than one muscle is functioning, complex movements of the disc are possible, including during the well-known ‘rooting’ behaviour of pigs, when the snout is used as a ‘plough’ to uproot bulbs, tubers, corms, roots, truffles and other underground food resources from soft soil. Bushpigs (Potamochoerus larvatus and Potamochoerus porcus) can produce 5–10–m-long, 10-cm-wide and 15–20-cm-deep ‘trenches’ in humid to wet soil during extensive rostral ploughing bouts.

The vastness of the facial musculature in Molarochoerus suggests that the rooting behaviour in this genus was extremely well developed, and it may indicate that the genus could plough in relatively hard substrates, or for extended periods of time. In support of the former suggestion, it is noted that the nasal bones in Molarochoerus appear to be dorso-ventrally thickened in comparison with those of Sus scrofa (Fig. 3-3), making them much more robust and thus stronger, presumably for resisting damage or bending forces while rooting.

The cheek tooth rows of Molarochoerus are unique within a suine framework, on account of the ventrally convex curvature of the occlusal surface of the upper cheek teeth in lateral view. In other suines, the upper cheek tooth row, in lateral view, is concave and the lower one is convex. This convex upper tooth row (and concave lower tooth row) curvature occurs in all adequately preserved material from Yuanmou, and is not due to post–mortem distortion.

Other unique features of the dentition of Molarochoerus concern the molarization of the posterior premolars, and the anterior shift of the area of maximal chewing forces from the molars towards the premolars. In the snout, PDYV 2000, wear of the cheek tooth row is greatest at P3/, P4/ and M1/, and the same applies to the mandible PDYV 1666. These teeth are at the centre of the curved cheek tooth row, and evidently absorb the greatest masticatory forces during chewing. Enlarged buccal roots of the upper teeth are clearly evident on the lateral surface of the maxilla, much more so than in Sus scrofa, for example, also indicating the concentration of masticatory forces in this region of the snout. In Sus scrofa and most other suines the chewing forces are concentrated further back along the tooth row, between M1/ and M3/, the latter tooth being the largest in the molar row. In Molarochoerus in contrast, the M3/ and m/3 are relatively small, the front two lophs of M3/ and m/3 being smaller than the M2/ and m/2, respectively.

The power of the masticatory forces appears to have been greater in Molarochoerus than it was in either Propotamochoerus or Microstonyx. The disto-sagittally directed parietal crests in the former genus differ from the more distally directed crests that occur in Microstonyx [7], which are almost parallel to each other, those of Propotamochoerus, which converge distally at a more gentle angle [13], indicating that there is more room for expanded masseter muscles in the anterior part of the post-orbital vacuity in Molarochoerus than in either of the other two genera. This morphology accords with the dental evidence. The anterior expansion of the space for the masseter muscles in the post-orbital region also accords with the suggestion that greater masticatory loads occurred anteriorly in the tooth row in comparison with the posterior tooth loading that typifies most suines.

The male mandible PDYV 0766 has an exceptionally robust anterior body, but the female specimens have more slender lower jaws.

All in all, it would appear that, not only was Molarochoerus endowed with massive snout musculature, but it was also provided with powerful chewing musculature. From this we infer that its masticatory behaviour was divergent from that of Sus scrofa, and species of Microstonyx and Potamochoerus. The observed splanchnocranial and dental differences suggest that the Yuanmou suid was ‘rooting’ in relatively hard substrates, perhaps for extended periods, and that the food that it ingested required tremendous masticatory forces.