Palaeohypsodontus zinensis, Métais & Antoine & Marivaux & Welcomme & Ducrocq, 2003
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publication ID |
https://doi.org/ 10.5281/zenodo.13345844 |
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persistent identifier |
https://treatment.plazi.org/id/AC06B12F-FFFE-872B-FFCA-79F7FD69A7F8 |
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treatment provided by |
Felipe |
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scientific name |
Palaeohypsodontus zinensis |
| status |
sp. nov. |
Palaeohypsodontus zinensis sp. nov. Métais
Figs. 4 View Fig , 5 View Fig ; Tables 1, 2.
Holotype: ISEM DBJ2 − A1 , fragmentary right mandible with d4−m1 (only the third lobe of d4 is preserved, Fig. 4 View Fig ).
Etymology: Named in reference of the Zin range which forms a prominent dome in the Bugti Hills’ landscape, especially from the locus where the specimens have been found.
Referred material.—Left astragalus (ISEM DBJ2−A2) and right fragmentary metatarsal bone (ISEM DBJ2−A3) cautiously referred to P. zinensis sp. nov ( Fig. 5 View Fig ).
tooth, and despite its advanced wear, it seems to be more brachydont than the first molar. The enamel is thin and the posthypocristid is transversally oriented. The distal extremity of the posthypocristid consists of a bulky structure which forms a distinct pillar in the postero−lingual corner of the tooth. Although the second lobe is broken, a weak ectostylid seems to occur between the latter and the third lobe. As in Miocene pecoran ruminants, the cusps join up in early wear stages, isolating a central cavity between both distal cusps. No cingulum can be distinguished on the rear of d4.
The molar (m1) is rectangular in occlusal outline and twice as long as it is wide. Lingual cusps are strongly compressed transversely and clearly higher than the labial ones, which are much more worn. The lingual wall of the tooth is rather flat. Only a narrow vertical groove occurs between the two lobes. The trigonid and talonid are equal in length but the trigonid is slightly narrower. No ectostylid occurs between the labial and strongly crescent cusps (protoconid and hypoconid). The stylids are not very bulbous, except for the relatively prominent entostylid which forms a postero−lingual pillar on the tooth. There is no trace of a Palaeomeryx fold on the protoconid or Dorcatherium fold, but a distinct metastylid occurs on the postmetacristid. This minute cusp extends on the lingual side of the teeth until the base forming a weak pillar. A strong mesial cingulum occurs in front of the tooth. The enamel is smooth. Measurements are provided in Table 1.
Postcranial material: two fragmentary postcranial remains (an eroded astragalus ISEM DBJ2−A2, and a fragmentary right metatarsal ISEM DBJ2−A3) were found in the same spot than the type specimen and they are thus tentatively referred to Palaeohypsodontus zinensis . The particular morphology of the astragalus is a key−apomorphy of the order Artiodactyla : in addition to the proximal trochlea, which articulates with the tibia, the astragalus also develops a distal trochlea articulating with tarsal bones. ISEM DBJ2−A2 seems to correspond to the size estimate range of the animal predicted from the dental remains ( Table 3). The body mass of both species of Palaeohypsodontus has been estimated from the area of the m1 ( Legendre 1989), and compared with estimates of body mass provided from the size of the astragalus ( Martinez and Sudre 1995; Table 3). We obtained body mass values significantly close enough (about 17.5 kg by using both methods) for considering dental remains and astragalus as belonging to the same species. The trochleas of the astragalus are not aligned, the distal one is shallower and slightly rotated medially with respect to the proximal one. Unfortunately, it is not possible to see if there was a ridge separating the articular surfaces of the cuboid and navicular, because the distal trochlea is badly broken. The sustentacular facet is mediolaterally convex and it occurs on the whole width of the plantar face. A weak ridge medially borders the sustentacular facet as in the astragali of Pecora ( Martinez and Sudre 1995). In lateral view, the fibular facet extends along the anterior part of proximal trochlea, but it is limited by an attenuated and longitudinal ridge near the apex of the trochlea.
The shaft of a right metatarsal is broken proximally and the section led to the conclusion that it probably belonged to a juvenile individual, because it lacks the distal epiphysis. The digit III and IV are not completely fused in sectional * indicate estimated values. view. Unfortunately, the state of preservation of the metatarsal gully does not allow us to see if it was open along its entire length, as living in bovids and giraffids, or closed at its distal end by a thin bridge, as in living cervids and moschids ( Heintz 1963). Measurements are provided in Table 2.
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