Phiomia 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 : 513-514

cf. Phiomia sp.

Fig. 6 .

Material.—Left M3? or M2 (CGM67199), distal part broken; left M3? (CGM67189); left m3 (CGM67187) from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt. For dimensions, see Table 1.

Description.—The three described molars have three transverse, paired cusps (trilophodonty) characteristic for proboscideans ( Tobien 1978). There is no cementum. The molars are relatively large compared to molars of other Paleogene proboscidean taxa but smaller than most Neogene elephantoids ( Sanders et al. 2010a), indicative of a palaeomastodont ( Sanders et al. 2010a). Molars are distinguished from Palaeomastodon by being bunodont, fully trilophodont, having narrow transverse valleys, a large accessory central conule in at least the first valley, well-formed wrinkled cingula and rather rugose enamel, and by the absence of pretrite and posttrite cristae ( Matsumoto 1924; Tobien 1978; Sanders et al. 2004). They most closely resemble those of the palaeomastodont Phiomia ( Tobien 1978: figs. 12–21; Sanders et al. 2004: figs. 7–10).

CGM67199 ( Fig. 6A ), a left molar, its estimated original width of 49 mm ( Table 1), indicating a M3, or may be M2 ( Matsumoto 1924), with multiple fractures.Due to these fractures and dental wear, adaxial conelets are not discernable anymore. It has a complete protoloph(id) and second loph(id), and a crushed tritoloph(id), with only some remnants of the posterior cingulum. Because of this damage, it is not possible to determine its position in the jaw with certainty. The proto- and second loph(id)s, as well as the posterior accessory conule, show considerable dental wear in the pretrite part. Thickness of the enamel has not been measured because of adhering sediments, as the molar has not yet been restored.

CGM67189 ( Fig. 6B ), probably a left M3, without dental wear, only slightly abraded, and showing a still rather rugose surface of the enamel. The molar had been larger in width, as at the pretrite some parts are missing. It has three well-developed lophs, though at the posttrite, the (labial) cone of the tritoloph is smaller than the other cones. Each cone has an adaxial, smaller conelet, except the protocone ( Tobien 1978: 187). There are two well-developed posterior accessory central conules, one in the first and one in the second transverse valley. The posterior cingulum is rather large and wrinkled. Thickness of the enamel has not been measured because of adhering sediments.

CGM67187 ( Fig. 6C ), a fragment of a left m3, slightly worn. The thickness of the enamel at the base of the crown ranges from 2.0– 3.4 mm. The surface is rather smooth with some traces of rugosities especially in the valleys. Most of the lingual posttrite is preserved; the labial half, the pretrite with the dominant cusps ( Sanders 2004), is broken in a longitudinal direction and lacking. The metaconid is also broken in half; the protoconid is lacking. Enough of the tritolophid is preserved to tell the place in the jaw. A wear facet is to be seen on the endoconid ( Fig. 6C 1 , white arrow). An adaxial conelet is present on the metaconid, endoconid and on the posttrite and pretrite cusps of the tritolophid. Due to the fragmentary state the anterior cingulum is absent, as is a large part of the posterior cingulum.

Remarks.—The Palaeomastodontidae ( Palaeomastodon , Phiomia ) comprise the earliest of the Elephantiformes . Based upon earlier interpretations of the age of the Jebel Qatrani Formation, earlier authors agreed about the late Eocene age of the first palaeomastodonts (e.g., Andrews 1906; Coppens et al. 1978). The general opinion is now that early Elephantiformes are not known before the early Oligocene, with the possible exception of Phiomia sp. indet. from the Evaporite Unit of Dor El-Talha, Libya ( Sanders et al. 2010a).

The estimated dimensions of the molars from Minqar Tibaghbagh seem to be only slightly smaller or as large as the largest comparable molars of Phiomia serridens from the Fayum Depression. The molars are, however, smaller than those of the late Oligocene molars of Phiomia major from the late Oligocene Chilga Formation of Ethiopia Sanders et al. 2004). See Fig. 7 and Age and stratigraphy.

Phiomia sp. indet. is known from the latest Eocene or early Oligocene of Libya ( Sanders et al. 2010a). Phiomia serridens (including P. minor , P. wintoni , and P. osborni ) is known form the early Oligocene of Egypt ( Andrews and Beadnell 1902), Libya ( Sanders et al. 2010a), from Tunisia ( Arambourg and Burollet 1962). Phiomia sp. indet. is known from the early Oligocene of Angola ( Sanders et al. 2010a). Phiomia major is known from the late Oligocene of Ethiopia in Africa ( Sanders et al. 2004). Phiomia sp. indet. is also known from the early Oligocene of Oman ( Sanders et al. 2010a) and the middle or late Oligocene of Saudi Arabia in Asia ( Zalmout et al. 2010).

Figures

Fig. 6. Molars of palaeomastodontid proboscideans cf. Phiomia sp. (A, B) and Phiomia sp. (C) from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt. A. Left M3 or M2 (CGM67199) in occlusal view (A1 stereopair; A2, reconstruction; A3, line drawing based on this reconstruction). A2 has been reconstructed by removing the fissures with Photoshop. B. Left M3? (CGM67189) in occlusal view (B1, photograph; B2, line drawing). C. Left m3 (CGM67187) in lingual (C1, arrow points at wear facet), buccal (C2), and occlusal (C3 stereopair; C4, reconstruction; C5, line drawing) views. C4 has been reconstructed by projection on a picture from Tobien (1978: fig. 19). Anterior is downwards. Scale bars 30 mm.

Fig. 1. Stratigraphic section of the Oligocene sediments at Minqar Tibaghbagh, Qattara Depression, Egypt. BOTM and BOS are indicated on the left of the section.

Fig. 7. Bivariate plots of Phiomia sp. cheek teeth from the BOTM, early Oligocene, Minqar Tibaghbagh, Qattara Depression, Egypt (stars) compared with Phiomia spp. from the early Oligocene Jebel Qatrani Formation, Fayum Depression, Egypt (diamonds) and Phiomia major from the late Oligocene, Chilga Formation of the Chilga Region, Ethiopia (triangles). Comparative dimensions of Phiomia serridens from Matsumoto (1924: 48, tables B, C, E, G); dimensions of Phiomia major from Sanders et al. (2004: table 2). A. M3? (or M2?) and M3?, originally the latter molar would have been larger in width (see text). B. m3, the width is based on estimated dimensions.