Fossil giraffes from the Miocene of Africa and a revision of the Phylogeny of the Giraffoidea

Abstract

Specimens of Climacoceras africanus are described from Maboko, Kenya. The new species Climacoceras gentryi is established on the basis of ossicones, mandibles, and upper and lower dentitions from Fort Ternan and Baringo, Kenya. By interpretation of its lower canines Climacoceras is identified as a giraffoid and is placed in the new family Climacoceridae. Canthumeryx sirtensis is identified from Muruarot and Rusinga, Kenya. A dentition and associated partial skeleton of this species are described. The teeth agree closely with specimens of the same species from Gebel Zelten, Libya. Zarafa zelteni from Gebel Zelten is synonymized with Canthumeryx sirtensis . Again on the basis of its lower canines Canthumeryx is identified as a giraffoid and is placed in the new family Canthumerycidae. Specimens of Palaeotragus primaevus are described from Baringo, Kenya. This material includes a cranium with the ossicones, skull roof, occipital and basicranial regions preserved. Palaeotragus primaevus specimens from Fort Ternan are used in this description and some of these are redescribed. The relations of the giraffoids are assessed by methods of phylogenetic systematics. Palaeomeryx, Prolibytherium and Propalaeoryx are excluded from the Giraffoidea as their lower canines are not known. The Palaeotraginae is shown to be an invalid polyphyletic grouping and the genus Palaeotragus is also shown to be polyphyletic. Palaeotragus microdon is probably synonymous with Palaeotragus rouenii and the three species Palaeotragus rouenii (P. microdn), Palaeotragus coelophrys and Palaeotragus quadricornis are retained in the genus Palaeotragus . It is suggested that 'Palaeotragus’ expectans and ‘Palaeotragus’ decipiens are closely related to Samotherium . Palaeotragus primaevus is probably synonymous with Palaeotragus tungurensis and this species is closely related to the giraffines. With slight changes the subfamilies Sivatheriinae and Giraffinae are valid monophyletic groups. Hydaspitherium is synonymized with Bramatherium and the Sivatheriinae includes the genera Giraffokeyx, Birgerbohlinia , Bramatherium and Sivatherium while the Giraffinae includes the genera Honanotherium, Bohlinia and and Giraffa and the species ' Palaeotragus ' tungurensis (P. primaevus). Okapia is identified as the sistergroup of the other giraffids. Triceromeryx is the sister-group of the Giraffidae. Canthumeryx is the sister-group of Triceromeryx plus the Giraffidae while Climacoceras is the sister-group of the other giraffoids.