Antilohyrax sp.

Vliet, Hendrik Jan Van, Schulp, Anne S., Abu El-Kheir, Gebely A. M. M., Paijmans, Theo M., Bosselaers, Mark & Underwood, Charles J., 2017, A new Oligocene site with terrestrial mammals and a selachian fauna from Minqar Tibaghbagh, the Western Desert of Egypt, Acta Palaeontologica Polonica 62 (3), pp. 509-525 : 515-516

cf. Antilohyrax sp.

Fig. 8 .

Material.—Incomplete left astragalus (CGM67188) from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt. For dimensions, see Table 2.

Description.—Left incomplete astragalus, CGM67188. In lateral view a distinctive rounded articulation fossa for the fibular malleolus is well preserved. In mediodorsal view the corpus of the astragalus shows proximally at the left side a deep concavity, the cotylar fossa. This morphology is typical for a hyracoid ( Rasmussen et al. 1990; Tabuce et al. 2007).

The tibial condyle of the astragalus is projecting laterally in a prominent way and there is a square-cut notch between this condyle and the lateral side of the neck, as in modern Procaviidae ( Rasmussen et al. 1990) . Bone fragments are missing from the navicular articulation distally at the plantar side. At the dorsal side, the distal articulation facet with the

cf. Antilohyrax sp. (CGM67188)

Antilohyrax pectidens (DPC7723a)

Thyrohyrax or Saghatherium ? (DPC7665)

Pachyhyrax crassidentatus ? (DPC6375)

)

mm

25

Pachyhyrax

Megalohyrax crassidentatus eocaenus ? (DPC

? (DPC

4515

3383

)

)

(

width

Medio-lateral 15

5

5 15 25 35 Lateral proximo-distal astragalus length (mm)

navicular has a smooth surface, indicating that no damage did occur. The distal facet is most probably saddle-shaped like that of Antilohyrax pectidens ( Rasmussen and Simons 2000) . This astragalus is of a medium sized hyracoid.

Remarks.—Postcranial remains of Paleogene hyracoids have not been extensively described ( Rasmussen et al. 1990: 4688). Only very few tarsal bones can be assigned with certainty to a certain species (Rasmussen and Gutiérrez 2010). The astragalus of Antilohyrax pectidens differs from all known hyracoid astragali by its saddle-shaped navicular facet (see Fig. 8D ; Rasmussen and Simons 2000). Because of some damage at the plantar side of the characteristic distal facet, and also at the cotylar fossa, dimensions of CGM67188 had to be estimated, but seem to have been rather similar to the astragalus DPC 7723a described and figured by Rasmussen and Simons 2000: 172–173, fig. 6). See Figs. 8D , 9 and Age and stratigraphy. We provisionally assign the astragalus to cf. Antilohyrax sp. , but emphasize that no other characteristic remains, e.g., the pectinate lower central incisors, were recovered. The genus Antilohyrax is thus far only known from the Quarry L-41 of the Fayum Depression in the lower sequence of the Jebel Qatrani Formation ( Rasmussen and Simons 2000). It would be the first co-occurrence of cf. Antilohyrax sp. and Phiomia sp. described; palaeomastodonts are not known with certainty from L-41 ( Seiffert 2010: 23).

The monospecific Antilohyrax pectidens is only known from the earliest Oligocene (or maybe the latest Eocene) of the Fayum Depression, Egypt in Africa ( Rasmussen and Simons 2000; Sanders 2010). Titanohyracidae are known from the Eocene and Oligocene of North Africa and the Miocene of Kenya (Rasmussen and Gutiérrez 2010).

Figures

Fig. 8. Left hyracoid astragalus, cf. Antilohyrax sp. (CGM67188) from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt, in plantar (A), lateral (B), and mediodorsal (C) views (photographs:A1–C1; explanatory drawings:A2–C2). D. Outline drawing of Antilohyrax pectidens from the Fayum Depression, Egypt in dorsal view, showing the similarities with the astragalus from Minqar Tibaghbagh (based on Rasmussen and Simons 2000: fig. 6b). Arrows point at the characteristic saddle-shaped navicular facet, broken parts indicated by dotted lines.