Cranial and dental morphology in a bohaiornithid enantiornithine with information on its tooth replacement pattern

Abstract

Despite the abundant number of enantiornithine fossils from the Jehol Biota, the cranial anatomy of these birds remains only superficially known. Similarly, data on dental replacement within this clade, and among toothed birds in general, is largely lacking. Here we describe a new and exquisitely preserved specimen of a bohaiornithid enantiornithine from the Lower Cretaceous Jiufotang Formation in Liaoning Province, northeastern China. The new specimen provides novel information on the cranial anatomy of these birds and unprecedented data on their tooth resorption, implantation, and replacement pattern, mostly visualized through computed laminography (CL) images. The new information demonstrates the presence of alternating tooth replacement with symmetrical signaling control, a pattern that is possibly shared by other enantiornithines. We also test the monophyly of Bohaiornithidae, one of the most species-rich groups of Jehol enantiornithines, through the addition of the new specimen. While our phylogenetic results support a monophyletic clade composed of several taxa traditionally included in this group (i.e., Bohaiornis, Sulcavis, Zhouornis, Longusunguis, and Parabohaiornis), it excludes Shenqiornis mengi, a species used to phylogenetically defined Bohaiornithidae. The fact that Shenqiornis is not resolved among the above-mentioned clade raises concerns about the usage of Bohaiornthidae as originally defined (i.e., most recent common ancestor of Shenqiornis mengi and Bohaiornis guoi, and all its descendants).