Fossil hyraxes (Hyracoidea: Mammalia) from the Late Miocene and Plio-Pleistocene of Africa, and the phylogeny of the Procaviidae

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Pickford, Martin
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A palate with much of the dentition from Aragai, Lukeino Formation (6 Ma) Kenya, is the most complete known specimen of a Late Miocene procaviid hyracoid. It shares several features with Dendrohyrax. The specimen is as large as the western tree hyrax, Dendrohyrax dorsalis, but it is attributed to a new species. D. dorsalis ranges through the tropical forests of Central and Western Africa, from Uganda to Gambia. As such the presence of a similar species at Lukeino provides evidence of the humid forest nature of the palaeoenvironment in the Tugen Hills during the Late Miocene. The fossil hyracoid specimens from the Early Pliocene of Langebaanweg, South Africa, are close in morphology to, but somewhat larger than, the extant bush hyrax, Heterohyrax brucei, but have some derived characters found in Procavia capensis. The cheek teeth are brachyodont, the lower premolar row is complete with a well-developed p/1 and there is a long diastema between the second incisor and the first premolar, all features recalling Heterohyrax. However, the depth of the mandible, the hypsodonty of the lower incisor, and the length of the premolar row relative to the length of the molar row are similar to the condition in Procavia and attest to the onset of molar enlargement relative to the rest of the dentition. In the overall context of the Procaviidae, Procavia is the most derived genus, and the presence of a few Procavia-like features in the Langebaanweg fossils indicate that the species concerned was probably already evident on the Procavia lineage, but the presence of several plesiomorphic characters reveals that it is a primitive member of the lineage. These also reveal that the specimens do not belong to Procavia cf. antiqua into which they were previously tentatively classified by Hendey (1976) as they are somewhat more derived. The detailed systematic status of the large extinct hyracoid Gigantohyrax maguirei, Kitching, 1965, from Pliocene cave fillings at Makapansgat, South Africa, has not previously been satisfactorily demonstrated, even though it is clear that most authors have considered it to be a procaviid closely related to Procavia. Kitching (1965) compared it only to species of Procavia. Re-study of the original sample, as well as additional fossils (three partial skulls, isolated upper premolar, fragment of mandible with a premolar) reveal that Gigantohyrax shares many features with the genus Dendrohyrax, fewer with Heterohyrax and even fewer with Procavia. It is concluded that among the Procaviidae, Gigantohyrax is most closely related to Dendrohyrax. The new discoveries of Late Miocene and Pliocene procaviids inKenya and SouthAfrica, when added to recently described associated upper and lower dental elements of Meroehyrax bateae from the base of the Middle Miocene of Uganda, permit a reappraisal of procaviid phylogeny. It is concluded that procaviids probably descended from Saghatheriidae, and that Pliohyracidae did not give rise to procaviids as previously thought by some authors.