The anatomy of two troodontid teeth from the Upper Cretaceous of Jiayin, Heilongjiang Province, China

The anatomical characteristics of troodontid teeth have remained largely unexplored. This study employs high-resolution computed tomography data to reconstruct and describe the morphology of two troodontid teeth, one newly discovered complete specimen and one previously documented specimen, from the Upper Cretaceous Yuliangzi Formation, located in the Sunwu–Jiayin Basin in Jiayin, Heilongjiang, northeastern China. The reconstruction reveals previously unrecognized anatomical features and presents the first three-dimensional visualization of the pulp cavity of troodontid teeth. Notably, the ratio of enamel thickness at the base of the crown to crown height is 0.19%. The enamel thickness on the labial side exceeds that on the lingual side in the mesial and distal denticles, a phenomenon observed for the first time in theropod teeth. The pulp cavity is distinctly narrow in the labiolingual dimension, tapers sharply toward the apex, and exhibits a distal curvature. It also displays nine distinct projections along the basal half of its distal margin. A wear facet is present, exhibiting an elliptical shape with parallel wear striations. Comparative morphological analysis identifies the new specimen as a Troodon -morphotype tooth, thereby providing further evidence for faunal exchange between North America and Asia via Cretaceous Beringia. Moreover, the only theropods that have been definitively identified from the Yuliangzi Formation are tyrannosaurids and troodontids. In addition, comparison of various dinosaur faunal assemblages within Maastrichtian deposits in China indicates that all of them contain tyrannosaurids.