Artiodactyla, Owen, 1848
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publication ID |
https://doi.org/ 10.5281/zenodo.13547406 |
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persistent identifier |
https://treatment.plazi.org/id/039EC237-E44F-FF9D-E27D-0ED3875BFE15 |
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treatment provided by |
Felipe |
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scientific name |
Artiodactyla |
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Artiodactyla indeterminate 1
Fig. 2A View Fig .
Material.—NMMP−KU 1556, a left maxillary fragment with?M2.
Locality.— The Pk5 locality (21°45´20˝N; 94°38´33˝E) in Myaing Township , western part of central Myanmar ( Fig. 1 View Fig ; Tsubamoto, Egi, et al. 2000) GoogleMaps .
Dental measurements.—M2 length = 10.5 mm; M2 width = 10.8 mm.
Description.—The preserved upper molar is bunodont and brachyodont, with seven distinct cusps (paracone, metacone, protocone, hypocone, paraconule, metaconule, and parastyle). The metacone is slightly smaller than the paracone and is as lingual as the paracone. The parastyle is located just mesial to the paracone. The ectoloph is weak and straight. The protocone is slightly distal to the paracone. The preprotocrista and postprotocrista extend to the paracone and metacone, respectively, bearing a paraconule and metaconule, respectively. The paraconule is worn more than the other cusps. The metaconule is larger than the paraconule and hypocone and is smaller than the paracone, metacone, and protocone. The hypocone is lingual to the protocone and is located just lingual to the metaconule. A cingulum surrounds the crown except for the lingual margin, bearing the parastyle and hypocone.
The present specimen preserves two (buccal and lingual) broken alveoli mesial to the preserved tooth. The lingual alveolus is located as distal as the buccal one, suggesting that the tooth for these alveoli is not P4 but M1 and that the preserved tooth is probably M2.
Discussion.—This specimen (NMMP−KU 1556) is assigned to the Artiodactyla on the basis of its enlarged metaconule. It is referable to such primitive bunodont artiodactyls as dichobunids or primitive entelodonts in having a brachyodont crown, conical cusps, a small hypocone, and a small paraconule. However, this upper molar differs from upper molars of primitive dichobunids such as Diacodexis and Eolantianius in being larger and in lacking V−shaped para− and metaconule cristae. It differs from upper molars of primitive entelodonts such as Brachyhyops (= Eoentelodon ) in having a larger parastyle, more distinct cristae, and less conical and less bunodont cusps. This specimen is morphologically unique and provides poor information, so its affinity among artiodactyls is unclear. Nevertheless, this specimen is not assignable to any mammalian species reported from the Pondaung Formation so far, suggesting an occurrence of an additional artiodactyl species in the Pondaung fauna.
Artiodactyla indeterminate 2
Fig. 2B, C View Fig .
Material.—NMMP−KU 1765, a right M2; NMMP−KU 1742, a right M3.
Locality.— The Pk12 locality (21°44´56˝N; 94°39´14˝E) in Myaing Township , western part of central Myanmar ( Fig. 1 View Fig ) GoogleMaps .
Dental measurements.—M2 length = 9.7 mm; M2 width = 10.7 mm; M3 length = 10.8 mm, M3 width = 10.7 mm.
Description.—M2 (NMMP−KU 1765; Fig. 2B View Fig ) shows the upper molar morphology of primitive bunodont artiodactyls such as helohyids and raoellids. The protocone is the largest cusp. The cusps are conical with weak cristae. The paraconule is tiny but distinct. The fourth cusp (metaconule or hypocone) is enlarged: it is nearly as large as the paracone and metacone but smaller than the protocone. There are no styles but there is enamel crenulation at the position of mesostyle. The cingulum is visible except at the lingual base of the protocone and the buccal base of the paracone. The dental enamel is somewhat wrinkled.
M3 (NMMP−KU 1742; Fig. 2C View Fig ) shows somewhat strange morphology and is triangular in occlusal view. The morphology of the mesial part (paracone−paraconule−protocone) is very similar to that of the present M2 although the paraconule is proportionally smaller on M3 than on M2. In the distal part (talon), the metacone is somewhat proportionally smaller than that of M2 and is more lingually located compared to the paracone. The fourth cusp is proportionally much smaller than that of M2, and seems to be located on a cingulum. The talon is distally elongated, bearing accessory cuspules on the distal margin of the cingulum.
Comparison and discussion.—We judged that NMMP−KU 1765 ( Fig. 2B View Fig ) is a right M2 and NMMP−KU 1742 ( Fig. 2C View Fig ) is a right M3, both of which probably belong to the same single individual. The two molars were found at the same locality. At the mesial margin of M3, there is an interstitial wear facet, which seems to match the distal interstitial wear facet of M2. There is no interstitial wear facet on the distal margin of M3. The two molars are very similar to each other in size, in morphology of the mesial part (paracone−paraconule−protocone), and in enamel and root colors. The M3 tooth wear is less progressed than the M2 tooth wear. The distal part of M3 is skewed compared to that of M2, and such a skewed distal part of M3 is often seen in M3 of various mammals.
Although the present upper molars are similar in morphology and size to those of helohyids and raoellids, the former differs from the latter two taxa in having buccolingually much more narrowed and distally much more elongated M3 talon. The present specimens further differ from those of Pakkokuhyus ( Helohyidae ) from the Pondaung Formation in having a lingual cingulum at the base of the fourth cusp and more wrinkled enamel, and in lacking weak but distinct proto− and metacristae directed mesiodistally.
The distally elongated M3 talon of the present specimen is reminiscent of that of several suoids such as Hyotherium , but the present molars seem not to be assignable to the Suoidea. The M3 differs from that of suoids in that the fourth cusp (metaconule or hypocone) is much smaller. A really distally elongated talon is an advanced character, and is not usually found in primitive Eocene suoids from Thailand, southern China, and North America ( Scott, 1940; Tong and Zhao 1986; Ducrocq 1994; Ducrocq et al. 1998; Liu 2001). Although M3 of an Eocene suoid Eocenchoerus from southern China ( Liu 2001) has a somewhat distally elongated talon with distal accessory cusps, its fourth cusp is much better developed than that of the present M3. Also, the M2 differs from that of suoids in having a smaller fourth cusp and a lingual cingulum at the base of the fourth cusp, and in lacking clear lingual separation into two (mesial and distal) lobes and an accessory cusp between the metacone and protocone.
These present specimens are also not assignable to any mammalian species reported from the Pondaung Formation so far, suggesting an occurrence of another additional artiodactyl species in the Pondaung fauna.
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