Dromaeosaurus albertensis Matthew & Brown 1922, new genus, new species

Dromaeosaurus albertensis , new genus, new species Type.— A. M. No. 5356, skull and lower jaws, and a few foot bones. Horizon and Locality.—Belly River formation, Red Deer River, Alberta. Found by Barnum Brown, Amer. Mus. Exped., 1914. Generic Diagnosis.— Comparable in size with Ornithomimus. Dental formula Pmx.? 3; Max. 9 Den.10 Teeth well developed, asymmetrically oval or compressed, sharp-pointed, recurved, serrate on anterior and posterior border. Premaxillary teeth three or more, not reduced in size, strongly convex antero-extemally but not of fully U-shaped section. Posterior teeth similar but more compressed and blade-like in both upper and lower jaw, the last maxillary tooth small. Jaws elongate, not massive. Orbital fenestra larger proportionately than in Deinodon, not so large as in Struthiomimus. Lateral temporal fenestra of good size, much as in Deinodon, not reduced as in Struthiomimus. Preorbital fenestras at present known only inferiorly, but evidently large. Frontals comparatively long and wide, the nasals overlapping them considerably, especially at the median line. The prefrontal and postfrontal sutures continuous, not separated by an orbital notch. Maxillo-premaxillary suture nearly vertical, the premaxilla large. The top of the skull is fragmentary and the specimen is at present only partly prepared, so that the above diagnosis will be completed and perhaps modified in some details in a later article. The skull is most like that of Deinodon in general proportions, but from a third to a fourth as large lineally, and but little larger than that of Struthiomimus altus. It differs from Deinodon in the reduced number of teeth, the large premaxillary teeth and the unsymmetric form of the maxillary teeth as well as in the light skull construction, large fenestrae and numerous details that might be largely associated with its small size. The foot bones are very different from those of either Deinodon or Struthiomimus, but so fragmentary that they are not positively identifiable, and no generic characters can be based upon them. The distal half of a metapodial, slightly larger than the me. II of Struthiomimus and only a little smaller than me. II of Deinodon (despite the enormous difference in size of the skeleton) has a deeply grooved ginglymoid distal facet, as in Deinodon, but shows a very distinct lateral appression surface. In Struthiomimus there is an appression surface on me. II, but the distal end of the bone is wholly different with a convex condylar facet; it also is of about the same size. Another much smaller metapodial has a less distinctly grooved distal facet and more irregular shaft that may be incomplete proximally. Of the phalanges there are three that fit so closely that they appear to belong with the metapodial first mentioned, but if so it must be the fourth digit, not the second, and may belong to the pes instead of the manus. A fourth phalanx is of similar type but distinct in details from any of the first three. A fifth is a proximal phalanx of size more suited to the smaller metapodial above mentioned, but does not fit it; it is rather short with concave basined head and laterally compressed distal end, apparently a phalanx of the first digit. A sixth phalanx is much larger than the others but only the distal end is preserved, its facet deeply grooved and very similar to the distal facet of the metapodial first noted. Possibly, but not probably, this is a median metapodial. The comparison of these bones with the complete manus and pes of Struthiomimus and of Deinodon shows clearly that Dromaeosaurus differs greatly in the construction of manus or pes, or both, from either of these genera and suggests a less degree of specialization and reduction of the digits in manus or pes. Although provisionally referred to the family Deinodontidae, the differences in the skull, number of teeth, and form of premaxillary teeth, together with the apparent diversity in construction of the foot bones, warrant placing Dromaeosaurus in a distinct subfamily Dromaeosaurinae.Published as part of Matthew, W. D., & Brown, B., 1922, The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta., pp. 365-385 in Bulletin of the American Museum of Natural History 56 on pages 383-385, DOI: 10.5281/zenodo.105379