Myorycteropus undetermined

Lehmann, Thomas, 2009, Phylogeny and systematics of the Orycteropodidae (Mammalia, Tubulidentata), Zoological Journal of the Linnean Society 155 (3), pp. 649-702 : 680-681

SPECIES MYORYCTEROPUS SP. ARRISDRIFT

Material (the specimens have not been directly seen by the author): Isolated teeth, maxilla, and mandible fragments, as well as isolated autopodes ( PQAD 2356; PQAD 2575; AD 330′94; AD 587′94; AD 159′96; AD 160′96; AD 408′96; AD 342′98; AD 94′00; AD 640′00) previously attributed to ‘ O. cf. minutus ’ ( Pickford, 1996) and later to ‘ O. minutus ’ ( Pickford, 2003) . They are tentatively referred to Myorycteropus in that work. The material is housed at the National Earth Science Museum, Windhoek, Namibia ( Namibia).

Locality and age: These specimens have been found at Arrisdrift ( GPS: 28°28′30″S, 16°42′20″E) ( Namibia), which is dated to between 17.5 and 17 Mya ( Pickford, 2003) .

Discussion: The small size of the material found at Arrisdrift is distinct from all other Orycteropodidae , except for the Myorycteropus and aff. M. minutus forms. The right M 2 found enclosed in a fragment of maxilla is similar in size to that of the holotype of M. africanus . However, it presents a deep lingual groove and a trapezoidal outline that is unlike those in the holotype of M. africanus . Note that there is no M 2 known for aff. M. minutus . The size of the lower molars is also very close to those found in the holotype of M. africanus , and the M 1 and M 2 (?) of aff. M. minutus . However, according to the figures presented by Pickford (2003), the lower molars have a rectangular outline as in M. africanus , and are unlike those in aff. M. minutus . Moreover, the angle between the two mandibular rami (character 17) can be measured on two of the three mandible fragments from Arrisdrift (AD 242′98 and AD 94′00). From the figures provided by Pickford (2003), the angles are between 55° and 60° (AD 242′98), and close to 75° (AD 94′00) (but see remarks). This is confusing, as a high angle (> 73°) is diagnostic of Amphiorycteropus , whereas a low angle (<60°) is the plesiomorphic state shown by Myorycteropus . The determination of the genus for this material is thus very delicate until direct observation can be made. Nonetheless, the small size of all elements, as well as the shallow angle of at least one of the mandibles, suggests a relationship with the genus Myorycteropus . Therefore, I recommend ‘faute de mieux’ a cautious determination of Myorycteropus sp. for the Arrisdrift specimens. The species level is not assessable with the available material. The determination made by Pickford (2003) is thus not followed here.

Remarks: The two mandibular fragments present fractures on the bases of their vertical ramus. Direct observations might confirm whether the mandibular angles measured are distorted by post-mortem deformation or not.