Ocepeia is an extinct genus of afrotherian mammal that lived in present-day Morocco during the middle Paleocene epoch, approximately 60 million years ago. First named and described in 2001, the type species is O. daouiensis from the Selandian stage of Morocco's Ouled Abdoun Basin. A second, larger species, O. grandis, is known from the Thanetian, a slightly younger stage in the same area. In life, the two species are estimated to have weighed about 3.5 kg (7.7 lb) and 10 kg (22 lb), respectively, and are believed to have been specialized leaf-eaters. The fossil skulls of Ocepeia are the oldest known afrotherian skulls, and the best-known of any Paleocene mammal in Africa. Ocepeia was initially grouped with the archaic ungulates known as "condylarths", but Ocepeia shares several features with primitive paenungulates (a group including elephants, hyraxes, sea cows and extinct relatives), but some analyses suggest it is more closely related to Afroinsectiphilia (a group containing aardvarks, golden moles, and tenrecs). As such, it may represent a transitional stage in the evolution of paenungulates from insectivore-like mammals. Unusual features of Ocepeia include skull bones with many air-spaces, and teeth and jaws reminiscent of those of simian primates. Ocepeia is distinct enough from other groups that it is placed in its own family, Ocepeiidae. Ocepeia lived at a time when northwest Africa was at the intersection of the Atlantic Ocean and the ancient Tethys Ocean, and much of the area was flooded by shallow, warm inland seas. Ocepeia fossils are associated with diverse sharks, birds, and marine reptiles, and a small number of early mammals, including other condylarths and early proboscideans. The early appearance and specialized features of Ocepeia suggest afrotherians originated and diversified within Africa, contrary to theories suggesting a more northern origin.
Discovery and naming
All specimens of Ocepeia come from the Ouled Abdoun Basin of Morocco, a phosphate basin. Research on Ocepeia has been carried out by French and Moroccan researchers led by Dr. Emmanuel Gheerbrant of the National Museum of Natural History in Paris. Ocepeia fossils have been recovered from the Grand Daoui, Meraa El Arech, and Sidi Chennane quarries, with the latter bearing the most complete specimens. Some of the original material was collected on-site as early as 1997, while other material was obtained from fossil dealers. Ocepeia was first described and named in 2001 by Gheerbrandt and Dr. Jean Sudre (University of Montpellier) based on two lower jaw fragments assigned to the new species O. daouiensis: one (designated CPSGM-MA1), bearing a premolar and first molar, is the holotype for the species. Additional material assigned to O. daouiensis was described in 2010, including a near-complete left lower jaw bone and additional dental fragments. In 2014, new specimens of O. daouiensis were described including a partial skull, upper jaw, and additional teeth, allowing for a complete reconstruction of what the intact skull looked like. The diversity of specimens, combined with CT scans of the partial skull, allowed for a much more detailed and comprehensive description. Additionally, new lower jaw fragments with larger teeth led to the description of O. grandis, whose holotype (designated MNHN.F PM37) bears a canine tooth and full set of cheek teeth. As of 2014, the skull of Ocepeia is the best-known mammal skull from the Paleocene of Africa (other species are only known from teeth or lower jaws), as well as the oldest known skull of any afrotherian.
Etymology The name Ocepeia derives from the initials of Office Chérifien des Phosphates (O.C.P.), the national Moroccan phosphate mining company that supported paleontological research in the Ouled Abdoun Basin, while the specific name daouiensis derives from Sidi Daoui, a fossil quarry within the Basin. O. grandis is named for its larger size compared to O. daouiensis, "grandis" meaning "large" or "great" in Latin.
Description
Ocepeia shows a mixture of primitive and highly derived traits, including features shared with primitive eutherian mammals as well as features similar to those seen in primitive ungulates ("condylarths") and early paenungulates. The skull of O. daouiensis was about 9 cm (3.5 in) in length and 5 cm (2.0 in) wide, estimated from reconstructions. O. grandis is known only from lower jaws with associated cheek teeth and isolated upper teeth. Estimates of body weight of O. daouiensis range between 8.5 kg (19 lb), estimated from tooth length, and 2.5 kg (5.5 lb), estimated from skull length. Using average values for all ungulates, Gheerbrant et al. found the most likely estimate was 3.5 kg (7.7 lb). The dental remains of O. grandis are about 1.5 times larger than O. daouiensis, giving an estimated weight of 10–12 kg (22–26 lb). In body mass and skull size, O. daouiensis is similar to modern-day hyraxes and the extinct Meniscotherium.
Cranium The cranium of O. daouiensis is known from two specimens: one consisting of a partial cranium including upper jaw material, the other consisting of an upper jaw (maxilla) with associated teeth. The former specimen is most complete, but lacks many of the fully-grown male features, so it is assigned to a young adult female. The later specimen is proportionally larger, although less complete, and possesses features such as large canine teeth that allow it to be assigned to a fully-grown male. The skull of O. daouiensis is generally robust. The skull has a short and thick snout, noticeably like that of a primate. The cranium of O. daouiensis was largely pneumatized (possessed numerous air spaces), with a greatly thickened supraoccipital bone. The cranial features Ocepeia shares with primitive eutherians include eye-sockets (orbits) set further back on the skull, relatively narrow cheek bones (zygomatic arches), and details of the inner ear, while characters it shares with paenungulates their paenungulate-like ancestors include a wide nasal cavity and a very short bony projection in the eye-socket. Pneumatized skulls are also found in larger proboscideans (e.g. elephants, mastodons, and other extinct relatives).
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