New data on the cranial morphology of the tapejarid Sinopterus from the Early Cretaceous Jehol Biota

ABSTRACTHere, we describe a new Jehol tapejarid skeleton tentatively referred to Sinopterus dongi, revealing some valuable cranial information about the palate and mandibular symphysis of this species. In the palate, the absence of the lateral process of the pterygoid indicates that the subtemporal fenestra is undivided, in contrast to the well-developed lateral process that subdivides the subtemporal and secondary subtemporal fenestrae in other azhdarchoids. The mandibular symphysis is elongated to about 58.7% of the mandible length, significantly longer than the other two Jehol tapejarids (52.9–53.7%) and much longer than other tapejarids (38.0–51.0%), except for the basal tapejarid Caupedactylus ybaka (~65%). The symphyseal shelf is extensive, flattened, and sculptured by sinuous ridges and pits. The ratio of its length to the symphysis is 34.4%, between that of the possible tapejarid Bakonydraco galaczi (43.9%) and the coexistent chaoyangopterid Eoazhdarcho liaoxiensis (26.7%), and much distinct from the well-reduced condition in other tapejarids. This discovery highlights the variation of the cranial morphology in the Tapejaridae and even the Azhdarchoidea.KEYWORDS: Jehol BiotaTapejaridaepalatemandibular symphysisSinopterus AcknowledgmentsWe thank two reviewers: Dr. Shu-An Ji (Institute of Geology, Chinese Academy of Geological Sciences, Beijing) and one anonymous reviewer for their reviews.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by the National Natural Science Foundation of China [42161134003]; Shandong Provincial Natural Science Foundation [ZR2017MD031]; Program for Innovative Research Team of Excellent Talents in University of Shandong Province [2019KJH004]; Taishan Scholar Program of Shandong Province [tsqn201812070].