Arcanotherium savagei ( Court, 1995 )

Delmer, Cyrille, 2009, Reassessment of the generic attribution of Numidotherium savagei and the homologies of lower incisors in proboscideans, Acta Palaeontologica Polonica 54 (4), pp. 561-580 : 563

Arcanotherium savagei ( Court, 1995)

Figs. 1–5 .

1995 Numidotherium savagei sp. nov.; Court 1995: 651, figs. 2–7.

Type material: Holotype: BMNH M. 82163a (field no. 6821/10), partial right mandibular ramus with p2–m3 . Paratypes: BMNH M. 82163b, partial left mandibular ramus with eroded m2–m3, undoubtedly from the same individual as the holotype (field no. 6821/?, listed by Court (1995) as m1–m2) ; BMNH M. 82167, left and right lower mesial incisors associated with holotype (field no. 6821/11) ; BMNH M. 82165, associated lower dentition comprising right p2–m2 and left p3–m3 (field no.686/2); BMNH M. 82168, isolated left m3 (field no.684/21, listed as 6821/21 by Court (1995); this is surely incorrect, as there are no more than 15 field numbers allocated to proboscideans from locality 6821); BMNH M. 82174, left scapular glenoid (field no. 6821/1); BMNH M. 82175, left ulna (field no. 6821/3); BMNH M. 82179, this specimen does not display any number), right cuneiform (field no. 6821/?, listed as 6821/9 by Court (1995)); BMNH M. 82180, right lunar (field no. 6821/8); BMNH M. 82177a–b, associated left and right femoral fragments (field nos. 6821/7–8); BMNH M. 82170, isolated left m2 talonid (field no. 684/11; listed by Court (1995) as 684/25; no specimen bearing this number is present in the collection, but 684/11 fits the description); BMNH M. 82169, right m3 (field no. 6955/1, mentioned by Court (1995) as a talonid of m3; this specimen is now complete, the missing protolophid having been found since in the collection); BMNH M. 82173, fragmentary atlas vertebra (field no. 6821/2); BMNH M. 82181,?metacarpal (field no. 6821/ 1); BMNH M. 82182,?metapodial (field no. 6821/14).

Type locality: Dor El Talha, Libya .

Type horizon: Idam Unit, early Oligocene.

Other referred specimens.— BMNH M. 82164, mandibular symphysis (field no. 686/2); BMNH M. 82166, right mandibular ramus with erupting p4 and m2, and numerous associated fragments of mandible and skull (field no. 686/8); BMNH M. 82183, partial symphysis with erupting mesial incisor (field no. 696/9); BMNH M. 82398, right M2 (field no. 686/2); BMNH M. 82171, lophid of indeterminate lower molar (field no. 684/32); BMNH M. 82172, right M1 (field no. 6816/3); MNHN LBE 20, left M1; MNHN LBE 30, fragmented upper molar; BMNH M. 82176, left ulna (field no. 6816/4); BMNH M. 82178, partial tibia (field no. 6821/4).

Emended diagnosis (modified from Court 1995).—Medium−sized proboscidean, intermediate in size between Numidotherium koholense and Barytherium grave . Mandible with a symphysis extending posteriorly to the level of p2 and an ascending ramus rising at the level of the junction between m2 and m3. Dental formula I?/i2 C?/c0 P?/p3 M3/m3; i 1 and i2 roots of similar size, those of i2 growing deeper in the symphysis; i1 mesio−lingually flattened, with distal edge crenulated buccally when unworn. Lophodont cheek dentition. Premolars more molarised than those of the early (non−elephantiform) proboscidean taxa Phosphatherium , Daouitherium , Numidotherium , Barytherium , and Moeritherium , with a metaconid distinguishable on p2 and strongly developed lingual to the protoconid on p3. Upper molars with a small paraconule, mesial to the protoloph, and massive mesial and lingual cingula.

Overall, the cheek dentition of Arcanotherium savagei is less lophodont than those of Barytherium and Numidotherium , with tips of cusps distinguishable and slightly elevated above the lophs. The scapula displays a tuberculum supraglenoidale which is smaller than that of B. grave and which lacks the distinct medially deflected coracoid process of N. koholense . The ulna of A. savagei shows a distinct lateral articular facet for the capitulum of the humerus, which is incipient in Barytherium and N. koholense , and a strong widening of its distal epiphysis. The lunate is wider anteriorly than posteriorly, with a small contact for the ulna. The cuneiform carpal is more rectangular than that of N. koholense , with a contact facet for the pisiform larger than that of deinotheres and elephantiforms.

Figures

Fig. 1. Holotype mandible (BMNH M. 82163a, b, c) of the proboscidean Arcanotherium savagei (Court, 1995), from the Idam Unit (early Oligocene) of Dor El Talha, Libya in occlusal (A), lateral (B), reconstructed occlusal (C) views.

Fig. 2. Mandibular elements of the proboscidean Arcanotherium savagei (Court, 1995), from the Evaporite Unit (late Eocene) of Dor El Talha, Libya. A. Symphysis (BMNH M. 82164) in occlusal (A1), lateral (A2), and anterior (A3) views; uncrushed incisor loci are outlined in white on A3. B. Part of right mandibular ramus (BMNH M. 82166) with erupting m2 and p4 in occlusal (B1) and lateral (B2) views.

Fig. 3. Dental elements of the proboscidean Arcanotherium savagei (Court, 1995), from the Evaporite (A and C, late Eocene) and Idam (B, early Oligocene) units of Dor El Talha, Libya. A. Erupting left i1 (BMNH M. 82183) in occlusal (A1), lateral (A2), and anterior (A3) views. B. Right M1 (BMNH M. 82172) in buccal (B1), occlusal (B2), and lingual (B3) views. C. Right M2 (BMNH M. 82398) in buccal (C1), occlusal (C2), and lingual (C3) views. D. Left M3 (MNHN LBE 20) in buccal (D1), occlusal (D2), and lingual (D3) views.

Fig. 4. Atlas (BMNH M. 82173) of the proboscidean Arcanotherium savagei (Court, 1995) from the Idam Unit (early Oligocene) of Dor El Talha, Libya in anterior (A), posterior (B) dorsal (C), and lateral (D) views.

Fig. 5. Ulnae of the proboscidean Arcanotherium savagei (Court, 1995), from the Idam Unit (early Oligocene) of Dor El Talha, Libya. A. Left ulna (BMNH M. 82176) in anterior (A1), lateral (A2), and proximal (A3) views. B. Left ulna (BMNH M. 82175), repaired since its first publication (Court 1995) in anterior (B1), lateral (B2), and proximal (B3) views.