A new basal phiomorph (Rodentia, Hystricognathi) from the late Oligocene of Lokone (Turkana Basin, Kenya)

ABSTRACT

Early hystricognathous rodents from Africa are primarily documented by two basal and extinct groups, the paraphyletic “Phiomyidae” and the Gaudeamuridae, which were particularly well diversified through the late Eocene and the early Oligocene. However, in the absence of a comprehensive late Oligocene fossil record, the evolutionary history of African hystricognathous rodents during the end of the Paleogene is unclear. Continuing field efforts in the Lokichar Basin of Kenya (western Turkana Basin) have led to the discovery of dental remains of a ‘phiomyid’ from the Lokone site LOK 13. The dental pattern of this rodent is unusual among ‘phiomyids,’ which led us to propose here a new taxon: Turkanamys hexalophus, gen. et sp. nov. Turkanamys shares a similar dental bauplan with early Afro-Asian hystricognaths (early ‘phiomyids’ and ‘baluchimyines’), and as such appears evolutionarily conservative with respect to some Oligocene and all the Miocene hystricognaths. Conversely, Turkanamys is also highly autapomorphic in developing a hexalophodont pattern on upper molars. The discovery of this peculiar rodent highlights the persistence of this ancestral ‘phiomorph’ group at the end of the Paleogene. Given the great familial diversity of hystricognaths in the early Miocene of East Africa, the virtual absence of their stem representatives in the late Oligocene record of the same province suggests either important taphonomic/sampling biases or a real absence of these families in this province at that time. This would suggest that hystricognathous rodents diversified elsewhere and colonized East Africa by the late Oligocene–early Miocene transition.

ACKNOWLEDGMENTS

We thank the Ministry of Science and Technology of Kenya for permission to conduct our research in the Turkana Basin. We acknowledge I. O. Farah (Director General of NMK), E. Mbua, M. Muungu, and the staff of the NMK for their assistance with collections and administrative authorizations. We are thankful to M. G. Leakey and R. E. Leakey, without whom the Lokone project would not have been initiated. We warmly thank J.-J. Tiercelin for his valuable help on the field. Logistical and field assistance were provided by M. Macharwas, F. Emekui, J. Makemkou, A. Londung, J. Manai, and people of Loperot and Lomeloku. Many thanks to M. Vianey-Liaud, A. Ramdarshan, J.-R. Boisserie, and P.-O. Antoine for advices and fruitful discussions on rodent evolution. Special thanks are extended to A.-L. Charruault and M. Orliac for technical assistances, and L. Meslin for scientific drawings. Finally, we thank the three anonymous reviewers, who have provided constructive remarks on the manuscript. The Agence Nationale de la Recherche (ANR) programs PALASIAFRICA ANR-08-JCJC-0017 (ANR-ERC) and ANR-09-BLAN-0238 supported this research. ISE-M publication no. 2012-001.

Handling editor: Guillermo Rougier