A fossil Monstersauria (Squamata: Anguimorpha) from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan

Abstract A nearly complete left dentary of a lizard was excavated from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan. The specimen shows several characters, which suggest its allocation in Monstersauria of the superfamily Varanoidea (Squamata: Anguimorpha). However, the specimen exhibits obvious differences from the known members of the whole Varanoidea. Thus, the specimen is described as a new taxon of cf. Monstersauria, Morohasaurus kamitakiens. This new species is characterized by a suit of unique features, such as the sinuous posteroventral rim of the dentary with a large U-shaped upper notch and small V-shaped lower notch, posteroventral corner of intramandibular septum with a weakly pointed eminence projecting posteriorly, and unicuspid, curved trenchant teeth with distinct blade-like carinae on their mesial and distal sides without grooves or serrations. Morohasaurus kamitakiensis might possibly be the oldest representative of the Monstersauria.