The first record of Tyrannoneustes (Thalattosuchia: Metriorhynchidae): a complete skull from the Callovian (late Middle Jurassic) of Germany

摘要

Thalattosuchian crocodiles belonging to the taxon Metriorhynchidae are among the first fossil reptiles ever discovered. Taxa belonging to this morphologically distinctive, stratigraphically long-lived, and widely spread group were described long before Richard Owen in 1841 coined the term "dinosaur" (e.g., Geosaurus giganteus described by von Soemmerring in 1814). Here we describe a new find of a Tyrannoneustes cf. lythrodectikos skull from the Callovian (late Middle Jurassic) of the Weser-Wiehengebirge (North Rhine-Westphalia, Germany). This species represents one of the oldest and most basal macrophagous metriorhynchines known to date. The new find is one of the most complete Tyrannoneustes skulls with both the cranium and the mandible found in association. It shows most of the autapomorphies typical of Tyrannoneustes lythrodectikos, some of which are not as distinctive as in the holotype. Additionally, it shows several characters of "Metriorhynchus" brachyrhynchus. Unfortunately, the current stage of publication leaves Metriorhynchus as a polyphyletic taxon that needs a proper redescription. The new specimen shows characters of both species, with slight variations that are too little to create a new species. Therefore, the specimen found near Munster was assigned to Tyrannoneustes cf. lythrodectikos. Several characters indicate a subadult ontogenetic stage for the specimen, consistent with its relatively small size compared with other Tyrannoneustes individuals.