Resumen de The mammal localities of Grand Daoui Quarries, Ouled Abdoun Basin, Morocco, Ypresian: a first survey

Emmanuel Gheerbrant, Jean Sudre, Henri Cappetta, Cécile Mourer-Chauviré, Estelle Bourdon, Mohamed Iarochene, Mbarek Amaghzaz, Baâdi Bouya

• English

  The unexpected discovery of mammals such as the earliest known proboscidean Phosphatherium escuilliei in the Ouled Abdoun phosphate Basin (Morocco), which is otherwise renowned for its very rich marine vertebrate fauna, has opened major new perspectives on the early African placental fauna. It was the impetus for several field parties by us between 1997 and 2001 which has allowed this survey of the geological, stratigraphic and paleontological context of Phosphatherium localities. This is the first important paleontological field work dealing with higher vertebrates in the Ouled Abdoun Basin since the work of C. Arambourg.

  Most of the material of Phosphatherium and other Ouled Abdoun mammals was found by local people searching for fossils for dealing, in an area where the economy is widely dominated by the mining development, in addition to more traditional but very poor agricultural resources. All Phosphatherium remains were found in the northeasternmost quarries of the Ouled Abdoun Basin, from a restricted quarrying area called Grand Daoui (fig. 3). In all Grand Daoui recognized localities (8), the mammals come from the lowermost Eocene level. The stratigraphically re-situated mammalian material was found in a bone-bed of the level called "Intercalaire Couches II/I" which is dated as early(iest) Ypresian on the basis of its relative stratigraphic position and its selachian fauna. At present, the occurrence of several mammal horizons in the "Intercalaire Couches II/I" (and Couche I ?) cannot be excluded, but their age difference seems not significant according to both the associated selachian taxa and the mammalian material, in present data. The bone-bed is very rich in macro-vertebrates. It includes especially large teeth of the shark Otodus obliquus which are the subject of very active research for dealing, and which explains the recent discovery of mammals such as Phosphatherium The level "Intercalaire Couches II/I" is made of a hardened phosphatic bioclastic limestone which is separated from underlying Paleocene levels by a major discontinuity. It is the first deposit of the Eocene sequence (megasequence C) in the Ouled Abdoun phosphate series. Deposition of this new sequence partly reworked the underlying Thanetian levels in the lowermost horizons of the level "Intercalaire Couches II/I", such as the mammals bearing bone-bed. This explains the recovery of Thanetian selachians in the matrix of the holotype of P. escuilliei and its initial allocation to the Thanetian by Gheerbrant et al. [1996, 1998]. These Thanetian selachian species are now clearly recognized as reworked. Studies of new samples of selachians associated with the newly recovered remains of P. escuilliei and other Grand Daoui mammals have confirmed our field observations owing to the identification of typical early Ypresian species which are listed in table I. P. escuilliei and other mammals from Grand Daoui quarries are confidently dated here as early(iest) Ypresian.

  As a general rule, there is no known concentration of fossil remains of species of terrestrial origin in the Ouled Abdoun epicontinental Basin. The mammals are exceedingly rare, documented by very few occurrences in contrast to the associated very rich marine vertebrate remains in the phosphate deposits. The occurrence of several rare mammals in these marine facies is related to a peculiar taphonomy characterized by a transport from near shores and continental hinterland under conditions of low hydrodynamic energy such as floated bodies. This is consistent with both the scattered nature of the material in the basin and with its well preserved state (e.g., dental rows, skulls) with respect to other early African mammal localities such as the Ouarzazate basin sites.

  Up to now, the Grand Daoui sites have yielded 7 species of mammals, which is not an inconsiderable diversity. The provisional faunal list includes a new hyaenodontid creodont, a small (P. escuilliei) and a large (Daouitherium rebouli) proboscidean, the two "condylarths" Abdounodus hamdii (cf. Mioclaneidae) and Ocepeia daouiensis (cf. Phenacodonta), and two indeterminate species which are described here. One of these, known only by a broken bilophodont lower molar, might belong to a new "condylarth" or a new ungulate. It has a reduced one-rooted M/3. An isolated M/3 belongs to another new species close to the genus Seggeurius. It is the oldest known hyracoidean along with an indeterminate species from the Ypresian of N'Tagourt 2 (Morocco).

  In the mammalian Ouled Abdoun « fauna », P. escuilliei is largely predominant. As a whole this "fauna" shows typical endemic African affinities. It provides new insight into the origin and initial radiation of major endemic African placental taxa. Despite their scarcity, the well preserved Ouled Abdoun mammal remains provide new data especially on the earliest known African ungulates. This is indeed the only known locality bearing large mammals in the Paleocene and early Eocene of Africa, probably in connection to the peculiar taphonomy of continental vertebrates in the phosphatic facies.

  The vertebrates associated with the Grand Daoui mammals include selachians, osteichthyans, marine reptiles (crocodilians, turtles, and the snakes Palaeophis) and also marine birds which are here reported for the first time in the Ouled Abdoun and other African phosphate basins. The Ouled Abdoun birds are diversified and much less rare than the mammals. They are the oldest known birds in Africa and among the oldest representatives of modern marine groups. Preliminary identifications indicate the occurrence of Procellariiformes (cf. Diomedeidae, cf. Procellariidae), Pelecaniformes (cf. Phaethontidae, cf. Prophaethontidae, cf. Fregatidae, cf. Pelagornithidae), and Anseriformes (cf. Presbyornithidae).

• français

  Nos recherches de terrain permettent de restituer le contexte géologique et stratigraphique d'origine des localités à Phosphatherium escuilliei (Proboscidea) du bassin à phosphates des Ouled Abdoun au Maroc. Le matériel de P. escuilliei et de plusieurs autres mammifères provient des exploitations de Grand Daoui (NE du bassin). Nos observations montrent que leur niveau d'origine est un bone-bed situé à la base de l'Intercalaire Couche II/I daté classiquement de l'Yprésien inférieur. Ces niveaux du début de l'Eocène marquent l'installation d'une nouvelle mégaséquence dans la série phosphatée qui a partiellement remanié les niveaux sous-jacents du Thanétien. Cela explique la présence de sélaciens du Thanétien dans la gangue de P. escuilliei et sa datation initiale du Paléocène. L'étude des sélaciens associés au nouveau matériel mammalien récolté confirme l'âge éocène basal de P. escuilliei avec l'identification de plusieurs espèces de l'Yprésien inférieur. La présence exceptionnelle de mammifères dans les Ouled Abdoun dénote d'une tapho-nomie particulière des restes continentaux dans les dépôts phosphatés. Ceux-ci ont été transportés dans le bassin depuis l'arrière-pays continental proche dans des conditions de faible énergie hydrodynamique, probablement sous forme de cadavres flottés. Au total le matériel récolté dans les carrières de Grand Daoui documente 7 espèces de mammifères dont un créodonte, deux proboscidiens, deux « condylarthres », et deux espèces indéterminées décrites ici. L'une est un des plus anciens hyracoïdes signalés. P. escuilliei est très largement prédominant parmi ces mammifères. La faune de vertébrés qui leur est associée comprend des restes d'oiseaux signalés pour la première fois dans les bassins à phosphates d'Afrique. Ce sont les plus anciens oiseaux connus en Afrique et parmi les premiers représentants des groupes marins modernes.