The mandible of Kronosaurus queenslandicus Longman, 1924 (Pliosauridae, Brachaucheniinae), from the Lower Cretaceous of northwest Queensland, Australia

Abstract

ABSTRACTThe complete mandible of the brachauchenine thalassophonean pliosaurid Kronosaurus queenslandicus Longman, 1924, is described for the first time from specimen KK F0630, discovered from the late Albian Allaru Mudstone, Rolling Downs Group, near Julia Creek, northwest Queensland. Previously undescribed anatomy results in several new features used to diagnose the taxon, including a mandibular symphysis exhibiting lateral embayments to accommodate overhanging premaxillary fangs and severe postsymphysis dentary constriction carrying embayments to accommodate large overhanging maxillary fangs. The presence of these embayments in specific areas on the lateral surface of the dentary and medial surface of the coronoid is a reflection of strongly developed anisodont dentition. The extension of a ventral dentary lamina posterior to a dorsal dentary lamina on the posterior margin of the dentary may represent a new character differentiating K. queenslandicus from K. boyacensis. Several differences are present between the mandible of KK F0630 and a previous composite reconstruction of the mandible of K. queenslandicus. The presence of six and a half pairs of functional alveoli within the mandibular symphysis in KK F0630 refutes prior research suggesting that K. queenslandicus bore three to four pairs of functional alveoli within the mandibular symphysis. A pathology exhibiting elongate grooves on the ventral surface of the right dentary is interpreted as a healed injury inflicted from the bite of a cretoxyrhinid lamniform shark. The discovery of KK F0630 further supports the notion that the late Albian Toolebuc Formation and Allaru Mudstone share similar fossil faunas.