Systematic approach to African Amphicyonidae not Hecubides
A classic problem with the palaeontology of carnivores is the relation between the upper and lower dentitions especially when there is scarce material, and/or which may belong to more than one species of the group, a situation which is quite common among the Amphicyonidae. The criterion of size on its own, with some exceptions, is difficult to apply on account of the presence of sexual dimorphism and bimodality, and because there is often overlap in dimensions of different species (Dehm, 1950).
However, seen in the light of African Amphicyonidae, neither Ysengrinia nor Agnotherium appear to be sustainable as valid genera for these African species.
3, table 4) is clearly larger than the specimen from Napak XV described as Hecubides euryodon, and is close in dimensions to Afrocyon ginsburgi, and while its poor preservation does not permit precise comparisons, it does indicate the presence of a second species of Amphicyonidae in the Sperrgebiet localities, which can be named Afrocyon sp.
This determination should be extended to the M2 from Lothagam described by Werdelin (2003) as Amphicyonidae species A, wich size is close to M2 from Ngorora species,
However, the majority of the more modern Amphicyonidae, even though they present a strong reduction of the protocone of P4, it is rarely retracted.
In summary, the Amphicyonidae hypothesis seems more plausible at the moment, two possibilities could give rise to this morphology; 1) from Afrocyon-Myacyon.
1.- Geographic location of African Miocene localities that have yielded Amphicyonidae remains.
4.- Comparison of the calcaneum of Amphicyonidae, dorsal view 1) Amphicyon sp.
Since the Early Miocene, prior to the appearance of the true bears, the Hemicyonidae show a rapid diversification that made of this group, along with the Amphicyonidae
, the predominant medium to large sized carnivorans until the beginning of the Late Miocene, when they became locally extinct, coinciding with the appearance of the Ursidae, Hyaenidae and Machairodontinae felids in the Western Europe faunas.