A stem lepidosireniform lungfish (Sarcopterygia: Dipnoi) from the Upper Eocene of Libya, North Africa and implications for Cenozoic lungfish evolution

Abstract

Modern lungfish are represented by three families, Neoceratodontidae in Australia, Protopteridae in Africa, and Lepidosirenidae in South America, with the latter two comprising the Lepidosireniformes. However, the group was far more diverse as recently as the Cretaceous. Here, a new lungfish, Xenoceratodus labyrinthus is described on the basis of upper and lower tooth-bearing elements from the Late Eocene of Dur at Talah, eastern Libya. Toothplates are characterized by four denticulations, low crests and ridges, and a well-developed crushing surface. The occlusal surface bears a unique ornament of enamel lines that branch to form a reticulate pattern across the crushing surface of the jaws. The new lungfish is closely related to the Paleocene Lavocatodus giganteus and the Late Cretaceous Lavocatodus? humei, which in turn are interpreted as a clade of stem Lepidosireniformes. Along with the presence of archaic lungfish lineages in the Cenozoic of South America and Australia, Xenoceratodus suggests that a wide range of lungfish lineages crossed the Cretaceous-Paleogene boundary, only to later become extinct; climate change and teleost radiation in the Cenozoic may have ultimately led to their decline.