A theropod tooth from the Middle Jurassic of Tibetan Plateau reveals convergent evolution of dromaeosaurid dental morphology

The Tibetan Plateau is among the least explored areas in terms of dinosaur paleontology in the world. Here we report a dromaeosaurid-like tooth from the Middle Jurassic Dongdaqiao Formation at the eastern part of the plateau. The tooth shows some dromaeosaurid dental features, including the absence of constriction at the cervix, a relatively small crown base ratio, a strongly recurved apex and lack of large transverse, and marginal undulations. Parsimony phylogenetic analyses using both dentition-based and complete morphological matrices support a dromaeosaurid affinity for this tooth, and place this Tibetan theropod as the sister taxon to Velociraptor. However, Bayesian tip dating analyses based on the velociraptorine affinity of the Tibetan tooth place the majority of the diversifications of early-diverging Paravian, particularly of dromaeosaurids, within or earlier than the Middle Jurassic, which is in conflict with the known paravian fossil records. Furthermore, our discriminate analysis based on morphometric data place the Tibetan theropod within Metriacanthosauridae. These results may suggest that the broad resemblances between the Tibetan specimen and velociraptorine teeth is due to convergent evolution. Other dromaeosaurid-like teeth reported from the Middle and Late Jurassic deposits of several sites in Asia and Europe are thus probably nondromaeosaurids as the Tibetan tooth is. Collectively, these suggest the presence of an early diverged theropod lineage with a wide geographical distribution and probably a dromaeosaurid-like dietary niche. This study highlights the importance of using multiple lines of data to identify fragmentary fossils.