Afrotragulus moruorotensis ( Pickford, 2001 )

Sánchez, Israel M., Quiralte, Victoria, Morales, Jorge & Pickford, Martin, 2010, A new genus of tragulid ruminant from the early Miocene of Kenya, Acta Palaeontologica Polonica 55 (2), pp. 177-187 : 179-181

Afrotragulus moruorotensis ( Pickford, 2001)

Fig. 2 .

doi:10.4202/app.2009.0087

2001 Dorcatherium moruorotensis Pickford, 2001: 438 , fig. 1.

Type material: Holotype: CMK Mor 1’2000, left hemimandible with m1–m3 ( Pickford 2001: fig. 1, table 1). Paratypes: Fragment of left maxilla with M2 and fragment of left maxilla with M3, both pertaining possibly to the same individual as the holotype ( Pickford 2001: fig. 1, table 1) and with the same catalogue number CMK Mor 1’2000; BMNH M82380 (right hemimandibular fragment with m3) and BMNH M82382 (left astragalus), both from same locality as the holotype ( Pickford 2001: table 1) .

Type locality: Moruorot , Turkana District, Kenya ( Pickford 2001) .

Type horizon: The Moruorot localities lie within the lower part of the Kalodirr Member of the Lothidok Formation, early Miocene ca. 16.8– 17.5 Mya ( Boschetto et al. 1992).

Emended diagnosis.— Afrotragulus with very elongated and narrow lower molars that show very mesio−distally enlarged and shallow central valley; almost continuous lingual wall due to both the great vertical development of the cristids and the alignment of the cusps; very flat lingual wall of the metaconid; very developed cristids that unite all cusps, with the exception of the distal part of the entoconid; developed post−hypocristid in the m1–2, which almost reach the linguo−distal corner of the teeth.

Description

Mandible and lower molars.—The mandible fragment of the holotype lacks the ventral border, nevertheless the mandible seems to be low as is typical in tragulids. The lower molars of Afrotragulus moruorotensis ( Fig. 2A, D ) are elongated and narrow. The distal lobe of both m1 and m2 is broader than the anterior lobe. The buccal cusps are crescent shaped. The metaconid is very flat and the cristids are high. The elongation of the lower molars enlarges the triangular central valley mesio−distally, making it markedly broad. This elongation cuts the contact between the pre−hypocristid and the anterior lobe. Moreover, the pre−hypocristid in Afrotragulus contacts the inner wall of the pre−entocristid. The cristids are very developed for a tragulid except the post−entocristid, which is absent, and unite all the main cusps at a medium degree of molar wear. Both the height and the extension of the cristids make the lower molars of Afrotragulus moruorotensis very selenodont for a tragulid. The Dorcatherium −fold is short and rounded, and the Tragulus −fold is absent; consequently, the “M”−structure is poorly developed. The entoconid is placed slightly forward with respect to the hypoconid. The post−hypocristid extends lingually but does not completely reach the disto−lingual corner of the tooth. There is no ectostylid. The anterior cingulid is strongly developed. The posterior cingulid is also robust in both the m1 and m2. Although part of the buccal and distal surfaces of the third lobe of the m3 are missing, this lobe is well developed, being typically tragulid in morphology: the hypoconulid has a strongly pointed tip and the lobe is linguo−distally open.

Upper molars.—The upper molars of Afrotragulus moruorotensis ( Fig. 2B, C ) have broad and low cusps with strongly developed mesostyle and buccal ribs. However, the cristae are somewhat longer than in Dorcatherium . The post−protocrista is short, but the pre−metaconulecrista is well developed. As occurs in A. parvus (as noted by Withworth 1958) A. moruorotensis has a strong lingual cingulum in the base of the protocone, and lacks an entostyle.

Astragalus.—The postcranial skeleton of Afrotragulus is poorly known. The astragalus ( BMNH M82382, Fig. 2E ) looks rather narrow and slender, with a markedly inclined and triangular proximo−plantar facet for the calcaneum.

Stratigraphic and geographic range.—“ Dorcatherium ” moruorotensis has been cited from Rusinga, Karungu, Arongo Uyoma and Mfwangano ( Kenya, lower Miocene; Pickford 2001). A form assigned to “ Dorcatherium ” sp. cf. “ Dorcatherium ” moruorotensis has been cited from the lower Miocene of the Sperrgebiet, Namibia ( Quiralte et al. 2008; see Discussion).

Figures

Fig. 2. Tragulid ruminant Afrotragulus moruorotensis (Pickford, 2001), Moruorot, late early Miocene of Kenya. A. Multi−focus photographs (A1–A3) and SEM (A4–A6) micrographs of the holotype Mor1’2000, left hemimandible with m1–m3, in occlusal (A1, A4), lingual (A2, A5) and buccal (A3, A6) views; B. Multi−focus photographs of the paratype CMK Mor 1’2000, fragment of left maxilla with M2 in occlusal (B1) and buccal (B2) views. C. Multi−focus photograph of the paratype CMK Mor 1’2000, fragment of left maxilla with M3, in occlusal view. D. BMNH M82380, right hemimandibular fragment with m3 in occlusal (D1), buccal (D2) and lingual (D3) views. E. BMNH M82382, left astragalus, in dorsal (E1) and plantar (E2) views.