Bothriogenys 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 : 516-517

cf. Bothriogenys sp.

Fig. 10 .

Material.—Right astragalus (CGM67197) from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt. For dimensions, see Table 3.

Description.—CGM67197, right astragalus. It has a proximal tibial and a distal cubonavicular trochlea, a “double pulley”, characteristic for an artiodactyl ( Rose 2006). In lateral view, an intra-articular fossa is discernible, a feature shared by many anthracotheriids ( Tsubamoto and Tsogtbaatar 2008). Overall morphoplogy is quite similar to that of Bothriogenys as figured by Andrews (1906: 188, fig. 61). Qatraniodon , the only known other anthracothere genus from the Jebel Qatrani Formation of the Fayum Depression, is excluded, as the holotype, a fragmentary dentary shows it to be a very small anthracotheriid ( Holroyd et al. 2010: 846).

The proximal inner condyle or medial trochlear ridge is intact. The proximal outer condyle or lateral trochlear ridge, that would have been larger than the medial trochlear ridge, is missing. While intact, the proximal trochlea had made an oblique angle with the distal trochlea, as is still to be seen in the slightly medially deviated medial tibial trochlear ridge. In dorsal view the tibial trochlea is preserved. In plantar view the convex, the inner and outer sustentacular facets, being the articulation sites with the calcaneus, are, although weathered, still visible. The sulcus separating both sustentacular facets is hardly discernible, because weathering has created some furrows. In dorsal view, a prominent and deep digital fossa is to be seen, the hinge for the distal anterocentral tibia flange. The distal trochlea is broken, so in plantar view both the navicular and cuboid facets are lacking, as is the distal calcaneal facet. In dorsal view, the cuboid facet at the distal trochlea is only partly broken, its medial limit being a ridge. The clear groove of the distal trochlea is visible. Most parts of the navicular facet are damaged.

Proximo-distal length Trochlea width Height medial N medial lateral tibial distal dorsoplantar

CGM67197 1 +56 (e58) +50 (e64) +30 (e32) +30 (e34) 31

Remarks.—In the Fayum Depression, the oldest known anthracothere, Bothriogenys sp. from the late Eocene Dir Abu Lifa Member of the Qasr El-Sagha Formation, is smaller than the early Oligocene Bothriogenys sp. of the Jebel Qatrani Formation described by Sileem and Hewaidy (2015). Bothriogenys species became larger in size through time ( Sileem and Hewaidy 2015). The dimensions of the astragalus of the BOTM at Minqar Tibaghbagh had to be estimated by a reconstruction, because of some damage. The original dimensions were probably larger than the late

40 60 80 100 Lateral proximo-distal astragalus length (mm)

Eocene specimen, but smaller than the early Oligocene specimens from the Fayum Depression, described by Sileem and Hewaidy (2015). See Fig. 11 and Age and stratigraphy.

The genus Bothriogenys is known from the Bartonian of Namibia ( Pickford 2015a), the late Eocene and early Oligocene of Egypt and maybe Tunisia ( Holroyd et al. 2010), the early Oligocene of Libya ( Coster et al. 2015), and perhaps the late Oligocene of Ethiopia ( Pickford 2015b) in Africa. In Asia, Bothriogenys is known from the probably early or middle late Eocene of Vietnam, early or middle late Eocene of Vietnam, the late Eocene of China and Saudi Arabia and the latest Eocene of Thailand ( Ducrocq et al. 2015), the late Eocene of Japan ( Tsubamoto et al. 2015) and the early Oligocene of Oman and Saudi Arabia ( Pickford 2015b).

Figures

Fig. 10. Right anthracotheriid astragalus, cf. Bothriogenys sp. from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt, in plantar (A), lateral (B), and dorsal (C) views (photographs, A1–C1; explanatory drawings, A2–C2). Missing, reconstructed parts indicated by dotted lines. Drawings reconstructed by projection on pictures from Sileem and Hewaidy (2015: fig. 5B2, B4, B1, respectively).

Fig. 11. Bivariate plot of an anthracotheriid astragalus, cf. Bothriogenys sp., from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt (star), compared with astragali of Bothriogenys sp., from the Jebel Qatrani (black and white triangles) and Qasr El-Sagha (grey triangle) formations of the Fayum Depression, Egypt. Original dimensions of the astragalus from Tibaghbagh have been estimated, because of damage. Dimensions of the other astragali are from Andrews (1906: fig. 61, black triangle) and Sileem and Hewaidy (2015: table 1, grey triangle and white triangles).