Talahphiomys libycus, Jaeger & Marivaux & Salem & Bilal & Benammi & Chaimanee & Duringer & Marandat & Métais & Schuster & Valentin & Brunet, 2010

Jaeger, Jean-Jacques, Marivaux, Laurent, Salem, Mustapha, Bilal, Awad Abolhassan, Benammi, Mouloud, Chaimanee, Yaowalak, Duringer, Philippe, Marandat, Bernard, Métais, Eddy, Schuster, Mathieu, Valentin, Xavier & Brunet, Michel, 2010, New rodent assemblages from the Eocene Dur At-Talah escarpment (Sahara of central Libya): systematic, biochronological, and palaeobiogeographical implications, Zoological Journal of the Linnean Society 160 (1), pp. 195-213 : 209-210

TALAHPHIOMYS LIBYCUS SP. NOV.

Holotype: DT1-022, a left M 1 (Fig. 5 V).

Referred material: DT1-020, left M 3; DT1-021, right M 2; DT1-023, right DP 4; DT1-024, left M 2; DT1-025, left M 3 (Fig. 5 T –Y).

Type locality and horizon: DT-Loc.1 (DT1), Idam Unit (‘Bioturbated Unit’) of the Dur At-Talah escarpment in central Libya.

Etymology: The species name is related to the country of the holotype, i.e. Libya.

Diagnosis: Species of the size of T. lavocati ( Wood, 1968) . Differs from this species in being less bunodont, in having more elevated transverse crests, and in showing upper molars characterized by a threecrested pattern including the protoloph, the posteroloph, and a mesoloph (-ule). M 2 displays an additional mesiolingual cingulum.

Description and comparisons: Only six isolated teeth (four uppers and two lowers) are referred to this new species of Talahphiomys . Although these teeth are the size of those of T. lavocati , they show a suite of characters that differs substantially from the type species of this new genus. The upper molars (Fig. 5 T – V) are slightly less bunodont compared with those of T. lavocati . In fact, the transverse crests (posteroloph and protoloph) are noticeably more elevated, and the anterior cingulum is practically an anteroloph (but still not connected to the protocone). One of the most distinctive characters is the presence of a mesoloph (-ule), which is long, strong on M 1 (Fig. 5 V), and shorter on M 2 (Fig. 5U). On M 1, the mesoloph (-ule) links the strong metaconule to the mesostyle that is situated on the buccal margin of the tooth, whereas on M 2 it links the metaconule to the mesiolingual side of the metacone. As in T. lavocati , the upper molars in T. libycus have virtually no metaloph, only a very short crest. There is neither endoloph nor mure, and the internal sinus is transverse. On M 1, the hypocone and protocone are mesiodistally aligned, whereas on M 2, the hypocone is slightly more buccal to the protocone. On M 3, the hypocone is much more buccal. This tooth is worn, but it seems that the hypocone and protocone were connected together by an endoloph.

A single upper premolar (Fig. 5W) is referred to T. libycus . This tooth is smaller than the molars, but is quite similar in morphology. Its anterior cingulum appears much lower, the protoloph is slender in its lingual part, and there is a thin, short, and very low crest linking the metaconule to the protocone, which partially closes the internal sinus.

The structure of these upper teeth is unusual amongst phiomyids. This dental pattern, characterized by a transverse sinus (because of the lack of both the endoloph and mure), the lack of a metaloph, and a long mesoloph (-ule), is somewhat reminiscent to that observed in Lophibaluchia , a baluchimyine from the Palaeogene of Pakistan ( Flynn et al., 1986; Marivaux & Welcomme, 2003). However, Lophibaluchia does not have a strong metaconule, and its transverse crests, notably the anteroloph, are much more developed. The two lower molars of T. libycus differ also from those of Lophibaluchia . As in T. lavocati , M 2 and M 3 in T. libycus lack the posterior arm of the protoconid, whereas in Lophibaluchia , this character is strongly developed and forms a metalophulid II ( Flynn et al., 1986: 35) Lower molars of Lophibaluchia are also strongly lophate compared to the condition observed in Talahphiomys . The fossil material documenting the lower molars of T. libycus is extremely limited and does not allow exhaustive comparisons. From the available material, it appears that the overall morphology of these teeth is very similar to that described for T. lavocati . Nonetheless, the morphology of the M 3 (Fig. 5Y) is somewhat special compared with that of the lower molars described for the genus. This tooth shows a vast talonid basin that is lingually closed by a strong, long, and elevated wall between the metaconid and entoconid. Additional material is necessary for better describing the lower dentition of this new species.