Marine vertebrate faunas from the Maastrichtian phosphates of Benguerir (Ganntour Basin, Morocco): Biostratigraphy, palaeobiogeography and palaeoecology

The Maastrichtian of Benguerir (eastern part of the Ganntour Basin, Morocco) consists of about 20 m of phosphates displaying an altemance of soft phosphate levels, marly horizons and hard phosphatic limestones. Isolated teeth of selachians, actinopterygians and marine reptiles are extremely numerous in these phosphatic. deposits and have been used for biostratigraphical, palaeodiversity and palaeoecological purposes. Detailed field work allowed to establish an exhaustive list of the Benguerir marine vertebrate faunas with their biostratigraphical distribution through five main fossiliferous levels (L6 to 12) spanning all the Maastrichtian. Their importance for biochronological purposes and correlations with other Maastrichtian phosphate deposits worldwide appears noteworthy. The selachians are currently represented by 60 species belonging to 32 genera and 7 orders. Among them, the genus Squalicorax is one of the most interesting concerning high-resolution biostratigraphy and correlations with other phosphate basins because of important rates of change noted between the 5 species recovered from base (e.g. occurrence of S. africanus) to top (e.g. strong representation of S. pristodontus) of the Maastrichtian. The marine reptiles include mainly mosasaurids but also scarcer plesiosaurs, chelonians and crocodyliforms, representing at least 14 taxa. The mosasaurid squamates are the most abundant and diversified with at least 8 species ranging all along the succession. The actinopterygians include mainly teleosts but also pycnodonts, also common in all levels and representing at least 7 taxa. Selachians and reptiles show the same trends, in terms of species richness per level, even if the reptiles are less informative due to a less diversified assemblage. For sharks, L6 and L2 show a high percentage of genera and species occurring only in the layer concerned. The evolution of diversity in actinopterygian fishes is less clear because of their low diversity. The use of dissimilarity indices and agglomerative method underscores two distinct associations: a lower one including the levels L6 and L5, and an upper one comprising the levels L4 to 12. These two associations allow to separate a lower and an upper Maastrichtian level and are important for correlations all around the southern and eastern margins of the Tethys. Another clear faunal turnover occurs between 13 and 12, because of a high appearance rate in L2 (at least in sharks) suggesting an increase in prey abundance, as testified by the rapid increase of marine predator density. Indeed, and through L6 to L2, a possible signal of an environmental damage affecting the predator community can be noted by faunal turnovers, even if no significant change in prey association was clearly detected. From a palaeobiogeographical point of view, the faunal associations of Benguerir appear typical of the southern and eastern margins of the Tethys, with several typical species not occurring in the northern Tethys. (C) 2014 Published by Elsevier B.V.