172


Journal of Paleontology 90(1):170–181 Holotype.—NHM M8449, left M3 (Table 1, Fig. 4.2).


Diagnosis.—Medium-sized anthracothere with dental formula 3.1.4.3.


Differs from contemporaneous Bothriogenys in having I3


caniniform, enlarged caniniform upper and lower canines, very short canine-P1/P1 diastema, no diastema between lower canine and I3, apex of P1–3 crowns situated almost midway between the roots, P1 peg-like and lacking triangular occlusal outline of P2 and P3,P2–3 mesial and distal crista oriented more mesiodistally rather than obliquely, upper molars with distinctive labial ribs (‘barrels’) on the labial slopes of the paracone and metacone (see Fig. 4.1–4.3), weakly-developed parastyle and metastyle, mesostyle bulbous and cuspate and not invaded by postpar- acrista and premetacrista, preparacrista weak and mesially oriented, labial cingula well-developed, strong lingual meta- cristule connected with lingual cingula, and very weak preprotocristae that never reach the paraconule, and leave a small valley between protocone and paraconule. Differs from Qatraniodon (Andrews, 1906; Ducrocq,


Figure 3. Nomenclature used to describe morphological features of the teeth of Nabotherium, following Lihoreau and Ducrocq (2007). Bold face indicates the main cusps of the tooth.


In the molar series, both the Fayum specimens and


Rhagatherium valdense have upper molars with mesostyles, but in R. valdense, the mesostyle is formed as a rounded crest connecting the postparacrista and premetacrista, after each turns labially to form parallel crests that extend nearly to the labial margin of the teeth. Also, the rounded crest forming the mesostylar connection bulges labially so that the labial extent reaches far beyond either the para- or metastylar shelves. In contrast, the Fayum specimens have small, cuspate mesostyles formed by weakly conjoined postpara- and premetacristae that do not run parallel to one another. In addition, the mesostyle does not extend labially beyond the parastyle, and extends only very weakly beyond the metastyle, especially on M2–3. The lower dentition of Nabotherium aegyptiacum differs


even more substantially from that of Rhagatherium valdense. True Rhagatherium has marked diastemata between the lower canine and P2, and between P2 and P3. Also, P1 is absent in Rhagatherium but present in Nabotherium. All three lower premolars of Rhagatherium are elongate and laterally com- pressed, whereas those of Nabotherium are relatively shorter and broader. The molars of Rhagatherium are also narrower, and M1 and M2 are subequal, unlike in Nabotherium and in anthracotheres in general, in which there is normally a size increase in molars from M1/1 to M3/3. These comparisons make it clear that the Fayum taxon


‘Rhagatherium’ aegyptiacum does not belong in the genus Rhagatherium as originally defined by Pictet (1857). To remedy this taxonomic situation, the new generic name Nabotherium is here proposed for the species.


Nabotherium aegyptiacum (Andrews, 1906) new combination 1906 Rhagatherium aegyptiacum Andrews, p. 192.


1997) in having much larger tooth dimensions, more bunodont molars that are relatively shorter and broader. Differs from the younger African taxon, Epirigenys Lihoreau, Boisserie, Manthi, and Ducrocq, 2015 (see Lihoreau et al., 2015), in lacking a distinct metaconid on P4, in having a more distinct protocone and shorter pre- and postprotocristae on P4, and in lacking an enlarged and mesially extended parastylar shelf on upper molars.


1928; Colbert, 1938) in having smaller tooth dimensions; M2 only slightly smaller than M3 (M2 much smaller than M3 in Anthracothema); upper molars with relatively larger and more robust mesostyles; upper molars with complete lingual cingula; M2–3 with much smaller anterior cingular cuspule;M3 with less basally inflated cusps; a more labiolingually constricted trigonid fovea, talonid basin, and hypoconulid fovea; and in possessing a well-developed premetacristid that connects to the preprotocris- tid, resulting in a closed trigonid basin. Differs from Myaingtherium Tsubamoto, Zin-Maung-


Differs from Anthracothema Pilgrim, 1928 (see Pilgrim,


Maung-Thein, Egi, Nishimura, Thaung-Htike, and Takai, 2011 (see Tsubamoto et al., 2011) in having a better developed protocone on P4,P4 and upper molars with lingual cingula, upper molars with mesostyles, shelf-like parastyles (both absent in Myaingtherium), much larger and crestiform paraconules, distinct pre- and postmetacristule (the latter closing off the talon basin distally), and in having distinct and lingually curving paracristids on P2–4. Differs from Anthracotherium magnum Cuvier, 1822


(NHM M28770, early Oligocene, Flonheim, Germany) in having less robust and more laterally compressed I2–3, a much less robust and more labiolingually compressed upper canine, P2 with a small protocone shelf, P3 with a relatively smaller protocone shelf and without a protocone cuspule, M2 only slightly smaller than M3, upper molars with complete lingual cingulum, and smaller mesostyles that do not project labially beyond the para- and metastyles, especially on M2–3.


Description.—Skull: Due to postmortem damage, the cranium of Nabotherium aegyptiacum (CGM 67200; Figs. 5–6) is


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