Dyrosaurid (Crocodyliformes: Mesoeucrocodylia) Fossils from the Upper Cretaceous and Paleogene of Mali: Implications for Phylogeny and Survivorship across the K/T Boundary

摘要

We describe new dyrosaurid fossils from three localities in Mali, representing strata of Maastrichtain, Paleocene. and Eocene ages. The fossils significantly extend the temporal and geographic ranges of several known dyrosaurid taxa. Rhabdognathus keiniensis and Chenanisuchus lateroculi are identified for the first time from Maastrichtian sediments. Additional material is referred to Phosphatosaurus gavialoides and, tentatively, the genus Sokotosuchus. These discoveries represent the First occurrence of Chenanisuchus and possibly of Sokotosuchus from Mali. Previously unknown morphological character states are incorporated into existing data matrices, reducing the amount of missing data. Phylogenetic analyses largely corroborate prior hypotheses of dyrosaurid relationships, but indicate a need for new characters to resolve the relationships of certain genera and species. The occurrence of both basal (e.g., Chenanisuchus lateroculi) and highly nested (e.g., Rhabdognathus keiniensis) members of Dyrosauridae on both sides of the K/T boundary indicates that dyrosaurid diversification was well underway by the latest Cretaceous, and that most, if not all dyrosaurid species survived the extinction event. The geology of the Mali's Tilemsi Valley is clarified; some rocks previously assigned to the Iullemmeden Basin actually represent extensions of other basins: the Taoudeni Basin and Gao Trench.