The anatomy and taxonomy of the North African Early Miocene crocodylian ‘<i>Tomistoma</i>’ <i>dowsoni</i> and the phylogenetic relationships of gavialoids

For decades, the interrelationships of the extant crocodylians <i>Gavialis gangeticus</i> and <i>Tomistoma schlegelii</i> have been debated, with only recent morphological phylogenetic analyses recovering the sister-taxon relationship between these two gavialoid species that has long been apparent in topologies based on molecular data. Several extinct species from the Mediterranean region are currently assigned to <i>Tomistoma</i>; however, their phylogenetic placement is labile, and often they do not form a clade with <i>Tomistoma schlegelii</i>. Here, we present a revision of <i>Tomistoma dowsoni</i> from the Early Miocene of Egypt and Libya, based on the type specimen (a partial snout and mandible) and referred material, including a nearly complete skull. These specimens show no notable anatomical differences and diagnostic features include: (1) a heart-shaped naris; (2) a prefrontal and lacrimal that are equidimensional in anteroposterior length; and (3) a prominent posterior process of the supraoccipital with a convex posterior margin. Maximum parsimony analysis, under both equal and extended implied weighting, recovers <i>Tomistoma dowsoni</i> as a phylogenetically nested gavialine, distantly related to <i>Tomistoma schlegelii</i> and other Mediterranean species currently referred to <i>Tomistoma</i>. Instead, <i>Tomistoma dowsoni</i> forms a sister-taxon relationship with <i>Eogavialis andrewsi</i>, from the Late Miocene of Kenya. Given that this clade does not consistently cluster with the type species of <i>Eogavialis</i>, and that <i>Tomistoma dowsoni</i> is diagnostic and clearly not referrable to <i>Tomistoma</i>, we herein erect the genus <i>Sutekhsuchus</i>, with the new combination <i>Sutekhsuchus dowsoni</i>. Our phylogenetic analyses recover the European Miocene gavialoids in a monophyletic group with the North American <i>Thecachampsa</i>, forming a clade of early-diverging gavialines that underwent transoceanic dispersal. We also recover a monophyletic group of thoracosaurs, comprising <i>Eothoracosaurus</i>, <i>Portugalosuchus</i>, and <i>Thoracosaurus</i>, which is expanded to include other Late Cretaceous–Early Paleogene European, North American, and North African species under extended implied weighting. https://zoobank.org/urn:lsid:zoobank.org:pub:2DE71417-8088-4749-8672-72E4A40C0B39