2 PROCEEDINGS OF THE NATIONAL MUSEUM vol.79 



Collected by George F. Sternberg, August 25, 1930. 

 Ty^ye locality. — About 9 miles SW. of Warren P. O., Buck Creek, 

 Niobrara County, Wyo. 

 Horizon. — Lance formation, Upper Cretaceous. 

 The specimen includes most of the upper half of the back portion 

 of the skull. The occipital border and the lateral border of the left 

 side forward of the infratemporal fenestra are preserved, thus fur- 

 nishing the full posterior width of the skull. Anteriorly the skull 

 is abruptly broken off back of the median prolongation of the front- 

 als. The median part of the massive dome was broken down prior 

 to discovery and much of its upper surface is missing, but enough 

 of the surrounding area remains to give a fairly accurate conception 

 of the full shape and extent. For the purpose of illustration the 

 missing part of the dome has been carefully modeled, following the 

 contours of the original adjacent surfaces, with the result shown in 

 Plate 1, Figure 1. 



The cranium-shaped enlargement is the outstanding feature of 

 the Troodon skull, the elevation having the form of a subovate boss 

 (pi. 2, fig. 2), that reaches its maximum height posterior to the line 

 of the orbits. At the center above the brain the estimated thickness 

 is not less than 180 mm. The central swelling is broadly convex 

 transversely but more moderately so in a longitudinal direction. 

 That this specimen is of a fully adult individual is indicated by the 

 coalescence of all sutures, few of which can now be distinguished. 



The dome surface is perfectly smooth and lacks the foramina and 

 markings so characteristic of the T. validns skulls. Fractured sur- 

 faces show the internal bone to be very dense as contrasted with the 

 more or less porous structure of the Belly River Troodonts. The 

 differences pointed out may, however, be only an age characteristic. 

 Viewed from above, the outline of the skull ends rather squarely 

 behind. At the base of the domelike enlargement, a broad shelf, 

 strongly overhanging the occiput, extends backward. The upper 

 surface of this shelf is only slightly less steeply inclined than the 

 surface of the dome itself. Thus, in profile it is quite unlike T. vali- 

 dns, in which the shelf forms nearly a right angle with the dome 

 mass. (Compare figs. 1 and 2, pi. 1.) The median part of the 

 parietal surface is devoid of ornamentation, as is the whole heavy, 

 rounded occipital border, in striking contrast to the ornate surface 

 of the T. validus skull. On either side of the smooth area, in the 

 position of the supratemporal fossae, is a large cluster of rounded 

 protuberances. Since parts of the skull are missing from both sides, 

 complete detailed information of this ornamentation is not available. 

 These rounded nodes have the appearance of each being on the 

 basal end of separate angularly cone-shaped ossifications that to- 

 gether completely fill the supratemporal fossa. In fact, it is clearly 



