Kritosaurus cf. Kritosaurus breviceps ( Marsh, 1889a ) (Marsh, 1889)

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 : 360

Kritosaurus cf. Kritosaurus breviceps ( Marsh, 1889a)

Figure 8U, V

Hadrosaurus breviceps MARSH, 1889a, p. 335.

Trachodon breviceps : MARSH, 1896a, p. 224.

? Kritosaurus breviceps : LULL AND WRIGHT, 1942, p. 170.

About a dozen teeth of a large flat-headed (hadrosaurine) ornithopod are present in the collections. AMNH 8525 consists of a crown (30 mm. long) making an obtuse angle of about 120 degrees with the fang (fig. 8U, V). The teeth are similar in size and morphology to each other and appear to belong to a single species. The crown is diamond-shaped with a bluntly rounded apex. A distinct medial keel is present above the slightly concave lateral edges. No ornamentation is found on the sides or keel. These teeth are probably referable to Kritosaurus , the only flat-headed ornithopod to be reported from the Judith River Formation (Lull and Wright, 1942, p. 171). The species was originally described by Marsh (1889a, p. 335) as Hadrosaurus breviceps , and later ( Marsh, 1896a, p. 224) as Trachodon breviceps . The systematic position of Hadrosaurus and Trachodon has been discussed at length by Sternberg (1936). Trachodon mirabilis seems to be more closely related to the crested lambeosaurines rather than to the flat-headed hadrosaurines. Sternberg (1936) has suggested that use of Trachodon mirabilis be abandoned.

Lull and Wright (1942, p. 171) described and figured the dental battery of K. breviceps obtained from the Judith River Formation. The teeth recently collected probably belong to the same species. Comparison of K. breviceps with other species of Kritosaurus from the Oldman Formation is of little use as the Judith River material is still not sufficiently well known.

Figures

FIG. 8. A. Chamops segnis. AMNH 8486, labial view of left dentary. B. Lingual view. Both x 5. C. AMNH 8488, lingual view of left maxilla. D. Labial view. Both x 5. E. cf. Xenosauridae, AMNH 8498, labial view of left maxilla. F. Lingual view. Both x 5. G. Peltosaurus piger, AMNH 8495, lingual view of left maxilla, x 5. H. AMNH 8494, lingual view of right dentary, x 5. I. Paraderma bogerti, AMNH 8504, lingual view of right maxilla. x 5. J. Parasaniwa wyomingensis, AMNH 8499, lingual view of left dentary, x 5. K. Leptochamops denticulatus, AMNH 8491, lingual view of right maxilla, x 5. L. Exostinus lancensis, AMNH 8497, lingual view of right maxilla, x 5. M. Deinodon horridus, AMNH 8513, posterior view of isolated tooth. N. Lateral view. Both x 13. 0. AMNH 8515, lateral view of anterior dentary tooth. P. Posterior view. Both x 13. Q. AMNH 8514, posterior view of?premaxillary tooth. R. Lateral view. Both x 12. S. Paronychodon lacustris, AMNH 8522, lingual view of isolated tooth. T. Labial view. Both x 12. U. Kritosaurus cf. K. breviceps, AMNH 8525, lateral view of isolated tooth. V. Posterior view. Both x 1 2. W. Procheneosaurus altidens, AMNH 8527, labial view of isolated tooth. X. Anterior or posterior view. Both x 12. Y, Z.?Sebecosuchia, AMNH 8549, views of an solated tooth. Both x 10.