Marine vertebrate fauna from the late Eocene Samlat Formation of Ad-Dakhla, southwestern Morocco

Abstract

AbstractLate Eocene deposits of the Samlat Formation, south of Ad-Dakhla city, southwestern Morocco, have yielded a mixed marine and terrestrial vertebrate fauna. Abundant and diversified chondrichthyans and archaeocete whales have been found, as well as the remains of sirenians and proboscideans. Here we describe the rest of this fossil assemblage which includes actinopterygians, turtles, palaeophiid snakes, crocodiles and pelagornithid seabirds. Actinopterygians are represented by at least two large-sized taxa, a scombroid probably close to the extantAcanthocybiumor to the EoceneAramichthys, and a siluriform related to the Ariidae. Turtles include at least four species represented by shell fragments. This mixed coastal and continental turtle fauna includes one littoral species of Podocnemididae, one or two deep-sea species of Dermochelyidae and one deep-sea species of Cheloniidae. Another turtle species is assigned to the terrestrial Testudinidae. Fragmentary crocodilian remains indicate the presence of undetermined eusuchians tentatively referred to Gavialidae and/or to Crocodylidae. Snake vertebrae are tentatively attributed to the genusPterosphenus(Palaeophiidae) pending the discovery of new material. Avian remains belong to a large pseudo-toothed bird (Pelagornithidae). Pseudo-tooth morphology resembles that of the late Oligocene – Neogene genusPelagornis. Additional bird remains are needed for a more precise taxonomic assignment. The fossil assemblage and palaeoenvironment of the upper Eocene deposits of the Samlat Formation appear closely related to those of the upper Eocene – lower Oligocene deposits of the Fayum (Egypt). The initial overview of this fauna provides an important contribution to the study of vertebrate evolution in North Africa near the Eocene–Oligocene transition.