Saurornitholestes langstoni (Figs. 1d, 3)

is the most common small theropod in the Judith River Formation of Dinosaur Provincial Park, judging from the number o: frontais (Tsble l) and teeth (Currie, Rigby and Sloan, in preparation) recovered. In contrast with Dromaeosaurus, the medial prong of the nasal does not extend as far caudally over the frontal as the more lateral prong. The slot that the lacrimal passes through the frontal to contact the prefrontal. is relatively small (Fig. 1d). The frontal is somewhat bulbous caudally where it curves posteroventrally to meet the parietal. A faint, sigmoidally curved ridge runs rostrolaterally onto the front margin of the postorbital process, and marks the anterior limit of the supratemporal fenestra. Unlike Dromaeosaurus, the portion of the frontal within the supratemporal fenestra is posterodorsally concave, and even forms a deep pit in some specimens ( TMP 86.77.57, Fig. 1d).