Dental eruption and adult dentition of the enigmatic ptolemaiid Qarunavus meyeri from the Oligocene of the Fayum Depression (Egypt) revealed by micro-computed tomography clarifies its phylogenetic position

The Palaeogene is a very important time period for mammalian evolution because it documents the first occurrence of many groups. One such group is the enigmatic Ptolemaiida, best known from the Early Oligocene of the Fayum Depression in Egypt, where it is represented by three genera, Ptolemaia, Qarunavus, and Cleopatrodon, including five species. Among these, Qarunavus meyeri is especially rare, as it is only known from two partial juvenile mandibles. Herein, the affinities of this taxon are re-investigated by applying micro-computed tomography (mu CT), thus enabling the study and comparison of its unerupted permanent dentition with that of other ptolemaiidans. The mu CT analysis confirms that Q. meyeri is a valid species, distinct from all other ptolemaiidans. Both the comparison and a phylogenetic analysis suggest a closer relationship of Qarunavus to the genus Cleopatrodon than to Ptolemaia; thereby, placing Qarunavus in the family Ptolemaiidae. Furthermore, the mu CT analysis enabled the assessment of the dental morphology of Q. meyeri revealing an unusual combination of traits, such as a very small single incisor next to a large canine. The eruption sequence of the permanent dentition in Q. meyeri implies a late dental eruption for the species, which would support the hypothesis of Ptolemaiida belonging to Afrotheria.