Orycteropus afer, SWARTKRANS

Lehmann, Thomas, 2009, Phylogeny and systematics of the Orycteropodidae (Mammalia, Tubulidentata), Zoological Journal of the Linnean Society 155 (3), pp. 649-702 : 685-686

SPECIES ORYCTEROPUS CF. AFER SWARTKRANS

Material: Distal part of a right humerus ( SKX 14261), housed at the Transvaal Museum, Pretoria. Lehmann (2004) revised this specimen and identified it as O. cf. afer .

Locality and age: Swartkrans, Member 1 ( South Africa), dated to around 1.8 Mya ( Brain, 1993).

Discussion: As described by Lehmann (2004: 312), the data collected on this distal humerus shows ‘that the South African fossil is closer to the Pleistocene species, all of the genus Orycteropus , than to Miocene forms like Myorycteropus MacInnes, 1956 , or Leptorycteropus Patterson, 1975 . In particular, the distal breadth of SKX 14261 is not significantly distinct from the data obtained for O. afer , and is strictly larger than all other Tubulidentata except O. crassidens ’. Moreover, the olecranon fossa of that specimen is oval and bounded proximally. This information confirms the generic attribution of that specimen to Orycteropus . The species level cannot be accurately identified. Therefore, I recommend following the cautious determination given by Lehmann (2004).

SPECIES ORYCTEROPUS CRASSIDENS MACINNES, 1956

Emended diagnosis: Large-sized species of Orycteropus (general dimensions equivalent to or larger than the largest specimens of O. afer ), which can be distinguished from the other species of the genus by the perpendicular orientation of the upper molars alveoli with respect to the palatine plan (as in M. africanus ), as well as the association of a large general body size (especially the post-cranial elements) with large molars. Orycteropus crassidens also shares the following unique characters with O. afer : the presence of an incisura mandibulae on the mandible, and the articulation axis of the semilunar notch on the ulna perpendicular to the diaphysis. Moreover, O. crassidens presents a deep lingual groove on the upper molars (like O. afer , aff. A. pottieri , and aff. A. seni ).

Holotype: NHM M 21543 –NHM M 21569 (former field number 1811′50), partial skeleton, housed at the NHM, London.

Paratype: NHM M 15412 and associated elements (former field number Kanjera 1-1955), partial skeleton housed at the NHM, London .

Remarks: The reference number NHM M 15412 corresponds uniquely to the complete right and left humeri of that specimen. The other elements are not labelled. MacInnes (1956: 28) did not clearly designate this specimen as the paratype of the species, but only as a ‘referred specimen’. The author described the material from Kanjera at the same time as the holotype, and clearly attributed it to O. crassidens . Consequently, in accordance with the ICZN (Art. 72.4.5), this specimen represents, with the holotype, the type series of O. crassidens , and therefore it is the paratype.

Type locality: Rusinga Island ( Kiahera-Sienga area ; Nyamwita), Lake Victoria ( GPS: 0°26′S, 34°9′E) ( Kenya) .

Main occurrences: Type locality and Kanjera ( GPS: 0°20′S, 34°36′E) ( Kenya) .

Age: Pleistocene. MacInnes (1956) stated that the holotype was found in a pocket of Pleistocene gravel and alluvium. Moreover, according to Behrensmeyer et al. (1995), Kanjera is dated to between 1.5 and 0.5 Mya.

Discussion: As explained previously, Pickford (1975, 2005) relegated O. crassidens from its species level. This author also described new specimens from East Rudolf sites (KNM ER 875; KNM ER 876; KNM ER 877) that he referred to ‘ O. a. crassidens ’ ( Pickford, 1975). In regard to these new specimens and the types of O. crassidens, Pickford (1975: 81) suggested that: ‘These specimens form a group of Orycteropus close to O. afer both in size and postcranial morphology and are here classified as a subspecies of O. afer . [...] If O. a. crassidens were classified as a separate species from O. afer , the three lower Pleistocene partial skeletons from Rusinga [the holotype of O. crassidens , n.d.], Kanjera [the paratype of O. crassidens , n.d.], and East Rudolf [the additional material described by Pickford (1975), n.d.] would all have to be specifically separated, a view which seems to be extreme for deposits of closely comparable age’. First, I concur with this author: the specimens of O. crassidens form a group of Orycteropus close to O. afer . In the present analysis, these relationships resulted in the redefinition of the genus Orycteropus . Then, the three lower Pleistocene partial skeletons might actually be specifically separated. On the one hand, the fossil aardvarks from Rusinga and Kanjera belong to O. crassidens , whereas on the other hand the specimens from East Rudolf could belong to O. djourabensis , as suggested by Lehmann (2008b). The species O. crassidens would hence be known exclusively by its holotype and paratype.

Finally, MacInnes (1956: 35) provisionally referred an ungual phalanx (field number 1218′50, now labelled NHM M 21570 ) to O. crassidens . Patterson (1975: 205) also reported this specimen, but expressed some doubts: ‘This bone differs from the unguals of O. afer and of the Kanjera specimen of O. crassidens in characters that suggest less proficiency in digging. It may not be referable to the genus’. The revision of this specimen shows that, on its palmar aspects, this ungual phalanx lacks the typical heel of the Tubulidentata . Moreover, its distal extremity is broad, its proximal articular surface is oblique, and most of all, shows traces of a median crest. These characters, far from being less specialized, are very different from those normally present in the ungual phalanx of Orycteropodidae . Therefore, I recommend withdrawing this specimen from the hypodigm, as this specimen might not be a Tubulidentata at all.