Incisor Enamel Microstructure of Hystricognathous and Anomaluroid Rodents from the Earliest Oligocene of Dakhla, Atlantic Sahara (Morocco)

A new primate community from the earliest Oligocene of the Atlantic margin of Northwest Africa: Systematic, paleobiogeographic, and paleoenvironmental implications

We report a new Paleogene primate community discovered in the uppermost part of the Samlat Formation outcropping on the continental shore of the Rio de Oro, east of the Dakhla peninsula (in the south of Morocco, near the northern border of Mauritania). Fossils consist of isolated teeth, which were extracted by wet screening of estuarine sediments (DAK C2) dating from the earliest Oligocene (ca. 33.5 Ma). These dental remains testify to the presence of at least eight primate species, documenting distinct families, four of which are among the Anthropoidea (Oligopithecidae [Catopithecus aff. browni], Propliopithecidae [?Propliopithecus sp.], Parapithecidae [Abuqatrania cf. basiodontos], and Afrotarsiidae [Afrotarsius sp.]) and four in the Strepsirrhini (a Djebelemuridae [cf. 'Anchomomys' milleri], a Galagidae [Wadilemur cf. elegans], a possible lorisiform [Orogalago saintexuperyi gen. et sp. nov.], and a strepsirrhine of indeterminate affinities [Orolemur mermozi gen. et sp. nov.]). This record of various primates at Dakhla represents the first Oligocene primate community from Northwest Africa, especially from the Atlantic margin of that landmass. Considering primates plus rodents (especially hystricognaths), the taxonomic proximity at the generic (even specific) level between DAK C2 (Dakhla) and the famous Egyptian fossil-bearing localities of the Jebel Qatrani Formation (Fayum Depression), either dating from the latest Eocene (L-41) or from the early Oligocene, suggests the existence of an east-west 'trans-North African' environmental continuum during the latest Eocene-earliest Oligocene time interval. The particularly diverse mammal fauna from DAK C2, recorded within the time window of global climate deterioration characterizing the Eocene/Oligocene transition, suggests that this tropical region of northwest Africa was seemingly less affected, if at all, by the cooling and associated paleoenvironmental and biotic changes documented at that time or at least that the effects were delayed. The expected densely forested paleoenvironment bordering the western margin of North Africa at the beginning of the early Oligocene probably offered better tropical refugia than higher latitudes or more inland areas during the cooling episode.

New phiocricetomyine rodents (Hystricognathi) from the Jebel Qatrani Formation, Fayum Depression, Egypt

Background

The rich rodent assemblages from the Eocene-Oligocene deposits of the Jebel Qatrani Formation (Fayum Depression, Egypt) have important implications for our understanding of the origin and paleobiogeography of Hystricognathi, a diverse clade that is now represented by the Afro-Asiatic Hystricidae, New World Caviomorpha, and African Phiomorpha.

Methods

Here we present previously undescribed material of the enigmatic hystricognath clade Phiocricetomyinae, from two stratigraphic levels in the lower sequence of the Jebel Qatrani Formation-a new genus and species (Qatranimys safroutus) from the latest Eocene Locality 41 (~34 Ma, the oldest and most productive quarry in the formation) and additional material of Talahphiomys lavocati from that species' type locality, early Oligocene Quarry E (~31-33.2 Ma).

Results

The multiple specimens of Qatranimys safroutus from L-41 document almost the entire lower and upper dentition, as well as mandibular fragments and the first cranial remains known for a derived phiocricetomyine. Specimens from Quarry E allow us to expand comparisons with specimens from Libya (late Eocene of Dur at-Talah and early Oligocene of Zallah Oasis) that have been placed in T. lavocati, and we show that the Dur at-Talah and Zallah specimens do not pertain to this species. These observations leave the Fayum Quarry E as the only locality where T. lavocati occurs.