Arsinoitherium andrewsi LANKESTER , 1903

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 : 304

Arsinoitherium andrewsi LANKESTER, 1903

M a t e r i a l. ONHM TN 2017-04, right p/2; ONHM TN

2017-06, right p/4; ONHM TN 2017-03, right m/3.

D e s c r i p t i o n. Three embrithopod lower teeth were collected at the Omanitherium type locality ( Tab. 1, Textfig. 8). The moderately worn right p/2 and p/4 preserve only the ectolophids, which are w-shaped, with the central valley closer to the distal end than to the mesial end, the lingual sides of the teeth and the roots having been destroyed by gypsum crystal growth. On the buccal side of the tooth, there is a mesial cingulum that rises from the cervix towards the occlusal surface. The buccal valley slants distally as it descends from the occlusal surface towards the cervix. The roots are broken off.

The right m/3 is heavily worn and lacks the lingual half as well as the mesial root, also damaged by gypsum growth. The distal root is massive and slants strongly to the rear, indicating that the tooth is the third molar. The crown is composed of two angular crescents with a deep central valley on the buccal side. The talonid is broken off, but its root base is preserved as a small shelf behind the distal lophid.

D i s c u s s i o n. There has been a long-standing tradition by which all the arsinoitheres from the Fayum, Egypt, have been interpreted to comprise a single species, Arsinoitherium zittelli BEADNELL, 1902a ( Beadnell 1902a, b, Sanders et al. 2010a), with the large range of variation being interpreted as a case of sexual dimorphism ( Sanders et al. 2004). However, Pickford (2015a) considered that the range of morphological variation in the available samples was too great to be encompassed by a single species, and he accordingly resurrected the species Arsinoitherium andrewsi LANKESTER, 1903 , to which the Omani fossils show a strong resemblance (large talonid in the m/3, morphology of the P4/). The new fossils described herein accord with this interpretation, the form of the ectolophs of the lower premolars resembling those in the lower jaw attributed to Arsinoitherium andrewsi by Andrews (1906), and the probable presence of a talonid behind the second lophid of the m/3 (broken off but leaving a small shelf-like process above the root), which agrees with this species.