Mesaceratherium welcommi, 2010

Antoine, Pierre-Olivier, Downing, Kevin F., Crochet, Jean-Yves, Duranthon, Francis, Flynn, Lawrence J., Marivaux, Laurent, Métais, Grégoire, Rajpar, Abdul Rahim & Roohi, Ghazala, 2010, A revision of Aceratherium blanfordi Lydekker, 1884 (Mammalia: Rhinocerotidae) from the Early Miocene of Pakistan: postcranials as a key, Zoological Journal of the Linnean Society 160 (1), pp. 139-194 : 157-159

MESACERATHERIUM WELCOMMI ANTOINE & DOWNING SP. NOV. ( FIGS 8–10, 11C , 12C )

Rhinoceros Falconer & Cautley, 1846 : pl. 76, figs 12, 12a, 12b

Teleoceras blanfordi (partim) Pilgrim, 1912: 3, 30–32; pl. 7, figs 4, 7

Rhinoceros blandfordi (partim) Forster-Cooper, 1934: 589–594, text-figs 9A, 9C, 9E.

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« Dicerorhinus » cf. abeli (partim) Welcomme et al., 1997: 532, 535

? ‘ Dicerorhinus ’ cf. abeli (partim) Welcomme et al., 1997: 534, 535, 536

Rhinocerotini , indeterminate genus and species Downing, 2005: 1–8, figs 2–3

Mesaceratherium sp. Métais et al., 2009: 163, 164; table 2, fig. 5

Diagnosis: Differs from other species of Mesaceratherium by a shorter premolar series, a hypocone posterior to the metacone, and stronger than the protocone on P2, a protocone slightly constricted on P3–4 and deeply constricted on M1–2, lower cheek teeth with a constricted entoconid, and lower premolars without labial cingulum. Further differs from Mesaceratherium gaimersheimense by an upraised mandibular symphysis, a foramen mentale below the middle of p3, a thick and continuous protoloph on P2, the constant presence of a crochet on upper molars, a constricted entoconid but no lingual cingulid on lower premolars, and the occasional absence of d1/p1. Differs from Mesaceratherium paulhiacense by the presence of a lingual bridge on upper premolars (molariform in M. paulhiacense ), by a labial cingulum on upper molars, and the absence of a mesostyle on M2, in the curved magnum-facet and fused McIIIfacets on McII, fused calcaneus-facets 2 and 3 on the astragalus, the presence of a fibula-facet on the calcaneus, the proximal border of MtIII concave in anterior view, and in the presence of a distal widening of the diaphysis on MtIII.

Nomenclatural remark: This new species must be referred to as Mesaceratherium welcommi Antoine and Downing, 2010 , following article 50.1 and the ‘recommendation 50A concerning multiple authors’ of the International Code of Zoological Nomenclature (ICZN, 1999: 52, 182).

Figures

Figure 11. Morphological comparison amongst right scaphoids of four coeval fossil rhinocerotids (Early Miocene) referred to the genera Pleuroceros Roger, 1898 and Mesaceratherium Heissig, 1969, in lateral view. A, Pleuroceros blanfordi (Lydekker, 1884), Zinda Pir Dome, Pakistan; B, Pleuroceros pleuroceros (Duvernoy, 1853), Aquitaine Basin, France. 1. posterior height nearly equals anterior height; 2. robust and low bone; 3. shallow radial notch; 4. mediodistal tuberosity (thick in P. blanfordi but absent in P. pleuroceros); 5. small trapezium-facet; 6. flat magnum-facet; 7. prominent postero-proximal semilunate-facet; 8. no edge between anterodistal semilunate- and magnum-facets; C, Mesaceratherium welcommi sp. nov., Zinda Pir Dome, Pakistan; D, Mesaceratherium paulhiacense (Richard, 1937), Aquitaine Basin, France. 1. posterior height much exceeding anterior height; 2. slender and elevate bone; 3. deep radial notch; 4. small mediodistal tuberosity; 5. large trapezium-facet; 6. concave magnum-facet; 7. no posteroproximal semilunate-facet (smooth pad); 8. sharp edge between anterodistal semilunate- and magnum-facets. (B) and (D) modified after de Bonis (1973). Scale bar = 2 cm.

Figure 12. Morphological comparison amongst left astragali of four coeval fossil rhinocerotids (Early Miocene) referred to the genera Pleuroceros Roger, 1898 and Mesaceratherium Heissig, 1969, in lateral view. A, Pleuroceros blanfordi (Lydekker, 1884), Zinda Pir Dome, Pakistan; B, Pleuroceros pleuroceros (Duvernoy, 1853), Aquitaine Basin, France (reversed). 1. medial lip smaller than the lateral one; 2. lateral height much exceeding medial height; 3. robust, broad, and low bone; 4. deep trochlear notch; 5. broad and oblique fibula-facet; 6.high collum tali (with respect to total height); 7. medial tubercle low, salient, and laterally displaced.; C, Mesaceratherium welcommi sp. nov., Bugti Hills, Pakistan; D, Mesaceratherium paulhiacense (Richard, 1937), Aquitaine Basin, France. 1. medial lip nearly equals the lateral one in size; 2. lateral height nearly equals medial height; 3. slender, narrow, and elevated bone; 4. narrow trochlear notch; 5. narrower and less oblique fibula-facet; 6.high collum tali (but lower with respect to total height); 7. medial tubercle high, smooth, and not-laterally displaced. (B) and (D) modified after de Bonis (1973). Scale bar = 2 cm.