Microstonyx major
Creators: name: Made, Jan Van Der
name: Güleç, Erksin
name: Erkman, Ahmet Cem
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Artiodactyla
Suidae
Microstonyx
Microstonyx major

description: Microstonyx major (Gervais, 1848 –1852)
2.2. Material
58-HAY-2/43 – palate with left P 4 and M 1-2 and right M 1-3 from locality 2.
58-HAY-2/45 – anterior part of a skull with left I 1-2, Cf, and P 2 –M 3 and right I 1-2, Cf, and P 2 –M 3 from locality 2.
58-HAY-2/134 – premaxillae with left I 2-3 and right I 2 – Cf from locality 2.
58-HAY-2/237 – palate with right and left P 4 –M 3 from locality 2.
58-HAY-2/239 – skull with frontals and posterior part of the nasals, left zygomatic arch, and palate with right and left P 4 –M 3 from locality 2.
58-HAY-19/05 – mandible with left P 3 –M 3 and root of P 2 and right P 2 –M 3 from locality 19.
58-HAY-19/250 – left M 1 from locality 19.
58-HAY-19/251 – right M 3 from locality 19.
58-HAY-19/252 – left M 2 from locality 19.
2.3. Description and comparison
Skull 58-HAY-2/45 (Figure 3) lacks the posterior part and is damaged dorsally. The snout is elongate with diastemata between the I 2, I 3, Cf, and P 2. On the right side the distances P 2 – Cf and P 2 –I 3 are 44.4 and 74.2 mm, respectively. In recent Suidae, these distances are sexually bimodal and in both sexes increase at least until complete adulthood (van der Made, 1991). The P 2 – Cf distance is slightly more than in male and female skulls from Terrassa (IPS), Udabno (GSM; Georgia), Stratzing (KME), and Eldar (GSM; Azerbaijan), localities of MN10 to MN11, while it is less than in most males and females from Grebeniki (VMM), Concud (NHM; Spain), and Pikermi (NHM), all MN12, and an unknown locality at Maragah (NMW; Iran). There were no P 1. These teeth tend to disappear in the later samples, though this seems to be a very gradual process. On both sides there is a well-developed crista alveolaris above and behind the canine, which does not extend upwards (unlike in Potamochoerus, for instance). The palate extends> 8 mm behind the M 3. The foramina palatina are between the anterior lobes of the M 3. The zygomatic arches depart at a blunt angle from the side of the skull and are massive.
Another skull fragment (58-HAY-2/239; Figure 4) preserves part of the dorsal surface. The frontals are wide. What is preserved of the left zygomatic arch is not very massive, but this is probably due to the fact that the lower part is lacking, which is usually more inflated. The orbits are relatively, but not very, far behind the M 3. The later specimens of Microstonyx tend to have the orbit placed further back with respect to the cheek teeth, but the character is difficult to observe objectively. The posterior edge of the foramina palatina is at the level of the second lobe of the third molar. The palate extends well behind the third molar. The glenoid for the left mandibular condyle is preserved; it is saddle-shaped.
Palate 58-HAY-2/237 confirms some of the morphology described above. It also has complete sets of right and left cheek teeth, but again the first premolar is lacking because of reduction. The diastema between P 2 and canine on the left side is slightly smaller than in 58-HAY-2/45.
The upper incisors, including the I 1, are flattened and elongate (Figures 3 and 5, Table 1). The I 2 is very elongate as in most Suinae and some Tetraconodontinae. The I 1 assigned to Microstonyx major are less flattened (van der Made et al., 1993), while those assigned to M. e. brevidens are similar in their degree of flattening (van der Made, 1997). The Cf are small and simple. The cheek teeth of Microstonyx have often been described and these teeth do not present particularities. The M 3 have simple talons with a large main cusp. The measurements of the cheek teeth are given in Table 2, while Figures 6 and 7 compare the sizes of the upper cheek teeth of the different species. Teeth from Hippopotamodon sivalense and H. antiquus are clearly larger than those from Sivas. The teeth assigned to Microstonyx major tend to be larger than those assigned to M. erymanthius, but also have a greater range of variation, including also small specimens. The specimens from Sivas are well within the metrical ranges of M. major, but occasionally outside those of M. erymanthius (in particular in the M 3).
The mandible (Figure 8) has an elongate and relatively slender aspect, which is principally caused by the symphysis being elongate and narrow. The length of the symphysis is 86, the thickness is 22.7, and the minimum transverse width in this area is 48.3 mm. The posterior end is situated just before the P 2. The length of the diastema P 2 –C f is 64.5 mm. Symphysis length and P 2 –canine distance are sexually dimorphic and tend to increase at least until the individual is completely adult. It seems that these distances are longer in the geologically younger Microstonyx, but it is difficult to evaluate this because of variability. The specimen from locality 19, being female, has among the highest P 2 –canine distances of the available Microstonyx samples.
The lower dentition has the common morphology of the Suidae. The following details are of particular interest. The incisors are high crowned to a degree that is common in the Suinae. None of the specimens had a P 1. This tooth tends to disappear in the later samples, and does so somewhat more rapidly than the P 1. The P 4 are of the dicoryphochoerine type and have a large metaconid that is separate from the protoconid. The M 3 have third lobes with 2 major cusps. The complexity of this lobe is very variable in Microstonyx (van der Made et al., 1993). The lower cheek teeth are relatively small (Table 3), but within the ranges of the material assigned to Microstonyx major, as well as that assigned to Microstonyx erymanthius (Figures 7 and 9).
2.4. Taxonomical assignment
The elongate I 2 occurs in Suinae and Tetraconodontinae, but the latter subfamily has P 4 with only one main cusp.
The shape of the P 4 is of the dicoryphochoerine type, with a metaconid placed well lingually of the protoconid, whereas in the Suini, it is placed slightly behind and close to the protoconid. This points to the Dicoryphochoerini. The elongate and low I 3 differs from the shorter and higher tooth in Propotamochoerus, but is similar in Microstonyx and Hippopotamodon. The size of the cheek teeth is clearly smaller than in Hippopotamodon sivalense and H. antiquus. In most cases, the sizes of the cheek teeth are in the overlap of the material assigned to M. major and M. erymanthius, but in some cases they are just outside the range of the latter but still within the ranges of the former species. Therefore, we assign the material to H. major, but we note that a revision of the M. major - M. erymanthius material is necessary.
description: Published as part of Made, Jan Van Der, Güleç, Erksin & Erkman, Ahmet Cem, 2013, Microstonyx (Suidae, Artiodactyla) from the Upper Miocene of Hayranlı-Haliminhanı, Turkey, pp. 106-122 in Turkish Journal of Zoology 37 (1) on pages 110-114, DOI: 10.3906/zoo-1202-4, http://zenodo.org/record/10973662