Earliest Oligocene hystricognathous rodents from the Atlantic margin of northwestern Saharan Africa (Dakhla, Morocco): systematic, paleobiogeographical, and paleoenvironmental implications

ABSTRACT

Hystricognathous rodents are among the most common members of African mammal faunas of the mid-Paleogene, but their record has so far remained limited to North and northeast Africa. Here we report the first Paleogene record of hystricognaths from the Atlantic margin of North Africa. The fossils come from the westernmost part of the Sahara, east of the Dakhla peninsula, Morocco, from estuarine deposits dating to the earliest Oligocene (Dakhla level C₂ [DAK C₂]). Several tens of isolated teeth plus three jaw fragments document seven species of hystricognaths (Gaudeamus cf. aslius, G. cf. hylaeus, Phenacophiomys occidentalis, gen. et sp. nov., Birkamys aff. korai, Mubhammys atlanticus, sp. nov., Neophiomys minutus, sp. nov., and ?Phiocricetomys sp.). Despite the extensive east-west geographic distance, the majority of hystricognath taxa recorded in DAK C₂ document primarily close relatives of taxa that are known from a latest Eocene Egyptian locality (L-41) and from early Oligocene localities of both Egypt and Libya. This highlights the widespread east-west distribution of hystricognaths across North Africa, a distribution that reflects the existence of roughly similar tropical environmental conditions in northern latitudes of Africa at that time. The presence of seven hystricognath species plus five anomaluroid species in sympatry during the earliest Oligocene demonstrates that rodents were particularly diverse near the global cooling recorded at the Eocene-Oligocene transition. We describe and compare the species and new species of hystricognaths with their sub-coeval counterparts from northern and northeastern Africa and then discuss the paleobiogeographic and paleoenvironmental implications of that discovery.

http://zoobank.org/urn:lsid:zoobank.org:pub:4041680F-65A0-41D5-AF97-D6115A656F15

Citation for this article: Marivaux, L., S. Adnet, M. Benammi, R. Tabuce, J. Yans, and M. Benammi. 2017. Earliest Oligocene hystricognathous rodents from the Atlantic margin of northwestern Saharan Africa (Dakhla, Morocco): systematic, paleobiogeographical, and paleoenvironmental implications. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1357567.

ACKNOWLEDGMENTS

We are particularly indebted to H. Cappetta (ISE-M), S. Enault (ISE-M), J. Surault (iPHEP), I. Elkati, A. Tarmidi, M. Fouadasi, and the local people of Dakhla for their assistance during the successive field seasons. Many thanks to G. Barbe and B. D'Haeze for their great interest in the paleontological project in the Dakhla region. We are grateful to S. Unal (ISE-M), S. Jiquel (ISE-M), B. Marandat (ISE-M), and J. Surault (iPHEP) for their contribution in the picking of the fossil specimens from Porto Rico (Pto) and El Argoub (Arg). Many thanks to C. Noiret (Université de Namur, Belgium), who performed the chemostratigraphic analyses with J. Yans on the rock samples from Arg and Pto stratigraphic sections (detailed results to be published soon in another work). We gratefully thank P. M. C. Coster (Kansas University, Kansas City, Kansas, U.S.A.) and H. Sallam (Mansoura University, Cairo, Egypt), who kindly provided casts of fossil hystricognaths from Africa (Egypt and Libya). We also thank them for sharing brand-new fossil data and for fruitful discussions regarding the origin and historical biogeography of hystricognathous rodents (March 2015, in Santa Fe, New Mexico, U.S.A.). Laurent Marivaux warmly thanks M. Boivin (ISE-M) and M. Vianey-Liaud (ISE-M) for many interesting discussions on the rodent dental nomenclature and several taxonomic aspects. We are grateful to A.-L. Charruault (ISE-M) for having prepared the casts of the fossil rodents from Dakhla C₂. We also thank P. M. C. Coster and E. R. Seiffert (University of Southern California, Los Angeles, California, U.S.A.), who provided formal reviews of the manuscript that enhanced the final version. Finally, many thanks to C. Cazevieille (Montpellier RIO Imaging [MRI] and Institute for Neurosciences Montpellier [INM], France) for access to scanning electron microscope (SEM) facilities. This research was supported by the French ANR-ERC PALASIAFRICA (ANR-08-JCJC-0017) and ANR EVAH (ANR-09-BLAN-0238) programs, the MEDYNA program (Maghreb-Eu research staff exchange on geoDYnamics, geohazards and applied geology in Northwest Africa; FP7, PIRSES-GA-2013-612572), and by ISE-M UMR CNRS/UM/IRD/EPHE 5554 (Laboratoire de Paléontologie) and iPHEP UMR CNRS 7262. This is ISE-M publication 2017-122-Sud.