Troodon formosus Leidy, 1856

Sahni, Ashok, 1972, The vertebrate Fauna of the Judith River formation, Montana, Bulletin of the American Museum of Natural History 147 (6), pp. 319-416 : 359

Troodon formosus Leidy, 1856

Figure 9L, M

Troodon formosus LEIDY, 1856 , p. 72.

Troodon formosus : LAMBE, 1902, p. 47.

Polyodontosaurus grandis GILMORE, 1932 , p. 117.

Troodon formosus : RUSSELL, 1948, p. 629.

Troodon was originally described by Leidy (1856) on the basis of a single unworn tooth recovered by Hayden from the Judith River Formation. Leidy (1856, p. 72; 1860, pp. 147- 148) suggested that Troodon had lacertilian affinities. The genus was also considered to have lacertilian affinities by Lambe (1902, p. 47), who described a few teeth from the "Belly River Series" of Alberta. Stanton and Hatcher (1905) were the first to tentatively regard Troodon as a dinosaur. Russell (1948) showed that Troodon was a theropod and quite distinct from Stegoceras . Consequently, the synonymy of Stegoceras with Troodon , as proposed by Gilmore (1924) and supported by Brown and Schlaikjer (1943), is incorrect. Polyodontosaurus grandis Gilmore (1932) has been shown by Sternberg (1951) and McDowell and Bogert (1954) to be synonymous with Troodonformosus.

There are a number of teeth recently collected from the Judith River Formation that closely resemble the type specimen of Troodon formosus . AMNH 8518, from Clambank Hollow, is a small laterally compressed tooth in which the coarser serrations are found on the posterior, and the finer ones, on the anterior crest (fig. 9L, M). The serrations are much better developed than in teeth of Deinodon or Dromaeosaurus , and usually consist of small, well-separated conules. A wear facet is present on the internal side of the crown apex.

A tooth considered to belong to Troodon formosus , AMNH 8519, from Clambank Hollow, differs from AMNH 8518 in a number of minor features. The base of the tooth is not laterally compressed but is oval in cross section, and coarse denticles are present on both anterior and posterior sides of the relatively straighter crown. The tooth resembles GSC 8841 in these features ( Sternberg, 1945, pl. 70, figs. 2, 3). AMNH 8520 is probably from the posterior end of the dentary. Its crown height is about 3.4 mm., and the crown is linguolabially compressed with a slight constriction at its anterior junction with the crown. The anterior crest is distinct but not serrated, and the posterior crest has about 11 well-separated denticles. The tooth resembles ROM 1445 ( Russell, 1948, p. 628, fig. 10) although the latter is slightly larger.

Figures

FIG. 9. A, B. Edmontonia lorngiceps, AMNH 8543, lateral views of an isolated tooth, x 1. C, D. Palaeoscincus costatus, AMNH 8542, lateral views of an isolated tooth, x 12. E, F. Thescelosaurus cf. T. neglectus, AMNH 8536, lateral views of an isolated tooth, x 10. G, H. Ceratopsidae, AMNH 8540, lateral views of an unworn tooth, x 12. I. Dromaeosaurus albertensis, AMNH 8516, lateral view of an isolated tooth, x 12. J, K. Paronychodon lacustris, AMNH 98523, lateral views of an isolated tooth, x 12. L, M. Troodon formosus, AMNH 8518, lateral ~~~~~~~~~~~~~~~~~~~~~~~~~~~~3. views of an isolated tooth, x 12. N. 0,?Stegoceras validus, AMNH 8530, lateral views of an isolated tooth, x 1-. Dinosaur egg shell fragments. P. AMNH 8545, external view of shell (Class B). Q. Internal view. Both x 10. R. AMNH 8546, external view of shell (Class B). S. Internal view. Both x 10. T. AMNH 8548, external view of shell (Class C). U. Internal view. Both x 10. V. AMNH 8547, external view of shell (Class B). W. In- ternal view. Both x 10. X. AMNH 8544, external view of shell (Class A), x 10.