Additional small theropod remains from the Upper Cretaceous Nenjiang Formation in Songliao Basin, Northeast China

Five new small theropod teeth and one manual ungual have recently been recovered from the Upper Cretaceous Nenjiang Formation in the Songliao Basin. The specimens were examined for their morphological characteristics, leading to the identification of four distinct taxa. The first taxon consists of three foliodont teeth characterized by a pronounced basal constriction and large hook-like distal denticles, which can be attributed to Troodontidae. The second taxon is represented by an elongated tooth featuring prominent longitudinal ridges, allowing for its assignment to Paronychodon. The third taxon is a blade-like tooth with notably small distal denticles, corresponding to Richardoestesia. The fourth taxon comprises a manual ungual characterized by a transversely wide and nearly symmetrical proximal articular surface, fully enclosed ventral foramina, a flattened ventral surface, and the absence of a flexor tubercle, resembling Alvarezsauridae. These specimens significantly enhance the known dinosaur diversity of the Nenjiang Formation and provide crucial insights for understanding the terrestrial ecosystem in Northeast Asia during the Late Cretaceous.