Troodon, Leidy, 1856

Currie, P. J., 1987, Theropods of the Judith River Formation of dinosaur Provincial Park, Alberta, Canada, Fourth Symposium on Mesozoic Terrestrial Ecosystems, Drumheller, Alberta: Tyrrell Museum of Paleontology, pp. 51-60 : 52

Troodon ( Currie 1985, 1987 a)

has an elongate, triangular frontal with a long orbital rim ( Figs. 1a , 2 ). A prefrontal has not been identified with certainty in troodontids, although a small, slender bone along the orbital rim of the frontal may be that bone ( Currie, 1985). The lacrimal suture encroaches onto the dorsal surface of the frontal, and ends caudally in a wall of bone. The dorsal surface of the frontal is concave in cross-section in the interorbital region, raised on both the midline and the orbital rim. A well defined ridge running from the medial edge of the frontoparietal suture to the deep, pit-like suture for the postorbital marks the anterior boundary of the supratemporal fenestra. As in ornithomimids, NMC 12355 and dromaeosaurids, the frontal provides very little area of bone for muscle attachment within the supratemporal fenestra.

Figures

FIG. 1 Theropod frontals from Dinosaur Provincial Park. (a) Troodon formosus. TMP 86.49. 10; (b) Dromicelomimus samueli, TMP 85.56.62; (c) cf. Erilcosaurus sp., NMC 12355; (d) Saurornitholestes langstoni, TMP 86. 77. 57; (e) Dromaeosaurus albertensis, NMC 12349, AMNH 5356; (f) cf. Aublysodon sp., TMP 80.16.485; (g) cf. Gorgosaurus libratus, TMP 80.16.924; (h) Daspletosaurus torosus (after Russell. 1970). (1) Caudal limit of dorsalateral exposure of the lacrimal; (2) caudal limit of orbital rim; (3) caudal limit of postorbital suture; (4) lacrimal slot; (5) Postorbital buttress. Scale= 1cm.

FIG. 2 Troodon formosııs TMP 86.49.10). Right frontal in (a) ventral, (b) dorsal, (c) lateral and (d) medial views. Scale= 1 cm.