Palaeomastodon ANDREWS , 1901b

Al-Kindi, Mohammed, Pickford, Martin, Al-Sinani, Yusouf, Al-Ismaili, Ibrahim, Hartman, Axel & Heward, Alan, 2017, Large Mammals From The Rupelian Of Oman - Recent Finds, Fossil Imprint 73 (3 - 4), pp. 300-321 : 312-313

Genus Palaeomastodon ANDREWS, 1901b or Phiomia ANDREWS et BEADNELL, 1902

M a t e r i a l. ONHM TQ 15, right P4/.

D e s c r i p t i o n. Aheavily worn bunodont right upper fourth premolar of a proboscidean (ONHM TQ 15: length × breadth: 25.0 × 25.6 mm) was found at Taqah ( Text-fig. 19 ). It was attributed to Omanitherium by Pickford (2015b) but the discovery of upper premolars of this genus at the type locality and nearby indicate that the identification was erroneous. The Taqah tooth is quadricuspidate, with low cingular remnants on the mesio-lingual corner of the protocone and the disto-buccal corner of the metacone, whereas the P4/ of Omanitherium is lophodont, with a weak or absent hypocone, the protocone and paracone are strongly joined together, and the paracone and metacone are linked together, signifying major differences from palaeomastodonts, in which the four cusps are distinct from each other, even in heavily worn specimens. The lingual, pretrite side of the tooth is more deeply worn than the buccal, post-trite side, as is usual in proboscideans ( Tobien 1978). Interstitial wear against the P3/ and M1/ has removed a considerable amount of the mesial and distal margins of the tooth, leaving small remnants of the cingula.

In the tooth from Taqah, the root beneath the protocone is contiguous with the one beneath the metacone, while the root that supports the paracone is distinct. This arrangement of the roots appears to be the usual pattern in moeritheres and palaeomastodontoids ( Tassy 1981).

D i s c u s s i o n. The P4/, ONHM TQ 15, was attributed to Omanitherium dhofarense by Pickford (2015b: fig. 4b), due to its dimensions, which are compatible with the holotype mandible, and due to its morphology, which mirrored the bunodont anterior cusps of the p/4 from the type locality. However, the discovery of a fully lophodont P4/ in the Ashawq Formation not far from the Omanitherium type locality prompted a re-examination of the Taqah specimen, and a deeper comparison to premolars of other proboscideans from Eo-Oligocene deposits of Africa. Study of the roots reveals that the tooth is a right P4/ ( Tassy 1981, Gheerbrant et al. 2005).

Appurtenance of this premolar to Moeritherium ANDREWS, 1901b , can be discounted, despite the compatibility in dimensions, because this genus has a weak to absent hypocone in the P4/ ( Andrews 1906: pl. VIII). The Taqah fossil is closest in terms of its morphology, dimensions and wear pattern to specimens of Palaeomastodon ( Andrews 1906: pl. XII) and Phiomia ( Andrews and Beadnell 1902) . Given the deeply worn condition of the crown, the identification is left open, with the balance somewhat favouring appurtenance to Palaeomastodon rather than to Phiomia .

Figures

Text-fig. 19. ONHM TQ 15, right P4/ of a palaeomastodontoid from Taqah, Dhofar Governorate, Oman. a) stereo radicular view, b) stereo occlusal view (scale bar 10 mm).